Analysing polypeptide antibiotics residues in animal muscle tissues: The crucial role of HRMS

A confirmatory method for the determination of polypeptide antibiotics (bacitracin, colistin, and polymyxin B) in muscle samples has been developed. Extraction is performed with acidified methanol, and a clean-up step by solid-phase extraction with polymeric cartridges is applied. Separation by ultra-high performance liquid chromatography (UHPLC) is carried out using a solid core C18 column and gradient elution with water/acetonitrile containing 0.2% formic acid. High-resolution mass spectrometry (HRMS) (Q-Orbitrap) detection using different working modes has proved to be highly advantageous in eliminating interfering signals from endogenous matrix components. The analytical method has been successfully validated according to Commission Regulation 2021/808/EU and is currently used in a public health laboratory involved in veterinary medicines residue surveillance activities.

Antimicrobial resistance profiles of Pseudomonas aeruginosa, Escherichia coli and Klebsiella pneumoniae strains isolated from broiler chickens

Globally, the spread of multidrug-resistant Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae from food to humans poses a severe threat to public health. The aim of this study was to assess the co-occurrence of colistin and β-lactamase resistance genes in E. coli, K. pneumoniae, and P. aeruginosa strains isolated from faeces of abattoir broiler chickens. The E. coli, P. aeruginosa and K. pneumoniae isolates were successfully detected from faecal samples by polymerase chain reaction (PCR) at infection rates of 60.7%, 22.5% and 16.7% respectively. The isolates displayed the highest levels of antibiotic resistance (AR) against ampicillin (82.3%) and amoxicillin-clavulanic acid (74.2%) for E. coli, followed by cefoxitin (70.6%) for K. pneumoniae, whilst P. aeruginosa displayed 26.1% antibiotic resistance (AR) against both ampicillin and colistin sulphate. The colistin mcr-1 gene was harboured by 46.8%, 47.1% and 21.7%, E. coli, K. pneumonia and P. aeruginosa isolates respectively. Ten out of 62 (16.1%), 6/17 (35.3%), 4/23 (17.4%) isolates were phenotypically classified as ESBL E. coli, K. pneumoniae, and P. aeruginosa respectively. The ESBL-E. coli isolates respectively possessed blaCTX-M (60%), blaTEM (20%) and blaCTX-M-9 (10%) genes. The ESBL-K. pneumoniae harboured, blaCTX-M (50%), blaOXA (33%), blaCARB (17%), and blaCTX-M-9 (17%) genes respectively, whilst, P. aeruginosa isolates respectively carried blaTEM (75%), blaCTX-M (50%), blaOXA (25%) and blaCARB (25%) genes. Molecular analysis identified the blaCTX-Mβ-lactamase-encoding genes collectively from E. coli, P. aeruginosa, K. pneumoniae isolates. Colistin and β-lactamase genes were present in only 16.7%, 6.9%, and 2.9% of E. coli, K. pneumoniae, and P. aeruginosa isolates, respectively. A total of 17, 7 and 3 isolates for E. coli, K. pneumoniae and P. aeruginosa respectively carried both colistin and β-lactamase antibiotics resistant genes. This is a public health threat that points to a challenge in the treatment of infections caused by these zoonotic bacteria. Data generated from this study will contribute to formulation of new strategies for combating spread of E. coli, K. pneumoniae, and P. aeruginosa isolates as well as prevention of their AR development.

Prevention of colistin-induced neurotoxicity: a narrative review of preclinical data

Polymyxin E or colistin is an effective antibiotic against MDR Gram-negative bacteria. Due to unwanted side effects, the use of this antibiotic has been limited for a long time, but in recent years, the widespread of MDR Gram-negative bacteria infections has led to its reintroduction. Neurotoxicity and nephrotoxicity are the significant dose-limiting adverse effects of colistin. Several agents with anti-inflammatory and antioxidant properties have been used for the prevention of colistin-induced neurotoxicity. This study aims to review the preclinical studies in this field to prepare guidance for future human studies. The data was achieved by searching PubMed, Scopus, and Google Scholar databases. All eligible pre-clinical studies performed on neuroprotective agents against colistin-induced neurotoxicity, which were published up to September 2023, were included. Finally, 16 studies (ten in vitro and eight in vivo) are reviewed. Apoptosis (in 13 studies), inflammatory (in four studies), and oxidative stress (in 14 studies) pathways are the most commonly reported pathways involved in colistin-induced neurotoxicity. The assessed compounds include non-herbal (e.g., ascorbic acid, rapamycin, and minocycline) and herbal (e.g., curcumin, rutin, baicalein, salidroside, and ginsenoside) agents. Besides these compounds, some other measures like transplantation of mitochondria and the use of nerve growth factor and mesenchymal stem cells could be motivating subjects for future research. Based on the data from experimental (in vitro and animal) studies, a combination of colistin with neuroprotective agents could prevent or decrease colistin-induced neurotoxicity. However, well-designed randomized clinical trials and human studies are essential for demonstrating efficacy.

Investigation of Escherichia coli isolates from pigs and humans for colistin resistance in Lao PDR- a cross-sectional study

Background

In Laos, colistin is not currently registered for use in humans. This One Health study aimed to estimate the prevalence of meat-producing pigs carrying colistin-resistant Escherichia coli, and investigate if E. coli causing invasive human infections were colistin-resistant.

Methods

Between September 2022 and March 2023, rectal swabs were collected from 895 pigs from abattoirs in 9/17 Lao provinces. Pig rectal swabs and stored E. coli isolates from human blood cultures, submitted to Mahosot Hospital Microbiology laboratory between 2005 and 2022, were screened for colistin resistance on selective chromogenic agar with organism identification confirmed using MALDI-TOF MS. Suspected colistin-resistant isolates underwent colistin susceptibility testing by broth microdilution following European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines. Isolates with MIC values of ≥2 μg/ml were tested for plasmid-mediated colistin resistance genes (mcr-1, mcr-2, and mcr-3) by multiplex SYBR Green PCR.

Results

A total of 15/620 (2.41%) invasive human E. coli isolates were phenotypically colistin-resistant by broth microdilution (MIC values 4 to 8 μg/ml). The earliest isolate was from 2015 in a patient from Phongsaly province in Northern Laos. A total of 582/895 (65.02%) pig rectal swab samples contained colistin-resistant E. coli. The detected colistin resistance genes were predominantly mcr-1 (57.8%, 346/598), followed by mcr-3 (20.23%,121/598), and 22.24% (133/598) were found to co-harbour mcr-1 and mcr-3. Among the 15 human isolates with colistin MIC values of ≥4 μg/ml, 12/15 were mcr-1.

Conclusions

We found that colistin resistant E. coli is causing invasive infection in humans in Laos despite the fact it is not available for human use. Use in animals seems to be widespread, confirmed by high carriage rates of colistin-resistant E. coli in pigs. It is probable that food-producing animals are the source of colistin-resistant E. coli bloodstream infection in Laos, although these have been infrequent to date. This is a serious public health concern in the region that needs to be addressed by appropriate enforceable legislation.

A molecular overview of the polymyxin-LPS interaction in the context of its mode of action and resistance development

With the rising incidences of antimicrobial resistance (AMR) and the diminishing options of novel antimicrobial agents, it is paramount to decipher the molecular mechanisms of action and the emergence of resistance to the existing drugs. Polymyxin, a cationic antimicrobial lipopeptide, is used to treat infections by Gram-negative bacterial pathogens as a last option. Though polymyxins were identified almost seventy years back, their use has been restricted owing to toxicity issues in humans. However, their clinical use has been increasing in recent times resulting in the rise of polymyxin resistance. Moreover, the detection of "mobile colistin resistance (mcr)" genes in the environment and their spread across the globe have complicated the scenario. The mechanism of polymyxin action and the development of resistance is not thoroughly understood. Specifically, the polymyxin-bacterial lipopolysaccharide (LPS) interaction is a challenging area of investigation. The use of advanced biophysical techniques and improvement in molecular dynamics simulation approaches have furthered our understanding of this interaction, which will help develop polymyxin analogs with better bactericidal effects and lesser toxicity in the future. In this review, we have delved deeper into the mechanisms of polymyxin-LPS interactions, highlighting several models proposed, and the mechanisms of polymyxin resistance development in some of the most critical Gram-negative pathogens.

Assessing the synergistic potential of bacteriophage endolysins and antimicrobial peptides for eradicating bacterial biofilms

Phage-encoded endolysins have emerged as a potential substitute to conventional antibiotics due to their exceptional benefits including host specificity, rapid host killing, least risk of resistance. In addition to their antibacterial potency and biofilm eradication properties, endolysins are reported to exhibit synergism with other antimicrobial agents. In this study, the synergistic potency of endolysins was dissected with antimicrobial peptides to enhance their therapeutic effectiveness. Recombinantly expressed and purified bacteriophage endolysin [T7 endolysin (T7L); and T4 endolysin (T4L)] proteins have been used to evaluate the broad-spectrum antibacterial efficacy using different bacterial strains. Antibacterial/biofilm eradication studies were performed in combination with different antimicrobial peptides (AMPs) such as colistin, nisin, and polymyxin B (PMB) to assess the endolysin's antimicrobial efficacy and their synergy with AMPs. In combination with T7L, polymyxin B and colistin effectively eradicated the biofilm of Pseudomonas aeruginosa and exhibited a synergistic effect. Further, a combination of T4L and nisin displayed a synergistic effect against Staphylococcus aureus biofilms. In summary, the obtained results endorse the theme of combinational therapy consisting of endolysins and AMPs as an effective remedy against the drug-resistant bacterial biofilms that are a serious concern in healthcare settings.

Acquired Bartter-like syndrome associated with colistin use in an adult patient: a case report

Colistin is an effective antibiotic utilized for the treatment of Gram-negative bacterial infections with coverage against a broad spectrum of bacteria. Despite the broad antibacterial coverage, this antibiotic can have serious complications such as acute kidney injury. Colistin also can have a toxic effect on the loop of Henle, causing tubulopathy, electrolyte imbalances, and the occurrence of Bartter-like syndrome (BLS) which is characterized by magnesium and calcium disturbances, polyuria, and metabolic alkalosis. We here report a 32-year-old male with a history of multiple trauma due to an accident that received colistin therapy for Pseudomonas isolation from wound culture on the 5th day of hospitalization. Polyuria, hypokalemic metabolic alkalosis, hypomagnesemia, and hypocalcemia were developed on the first week of colistin administration. The patient received colistin until the 21st day of hospitalization. Serum calcium and magnesium levels became normal 1 day after stopping colistin, while urine volume and metabolic alkalosis resolved 6 days after colistin discontinuing. Therefore, it is crucial to adjust the dose of colistin to minimize its toxicity.

Investigation of colistin utilization in the treatment of multidrug-resistant gram-negative nosocomial bloodstream ınfections in children and literature review

This retrospective study aimed to assess the effectiveness and safety of colistin used in combination therapy for treating nosocomial bloodstream infections caused by multi-drug resistant gram-negative pathogens in pediatric patients. Patients aged between 1 month and 18 years consecutively hospitalized with healthcare-associated bloodstream infections necessitating the administration of intravenous colistin at Dr. Sami Ulus Training and Research Hospital between January 2015 and January 2020 were included in the study. Patient-specific detailed clinical information, prognoses, and laboratory findings on days 1, 3, and 7 of colistin treatment were obtained from medical records. The study included 45 pediatric patients receiving intravenous colistin; 26 (57.8%) were male and 19 (42.2%) were female, with a median age of 18 months. While the clinical response was observed at 82.2% and microbiological response at 91.1% with colistin treatment, two patients (4.4%) discontinued treatment due to side effects without assessing treatment response. The most common adverse effect associated with the use of colistin was nephrotoxicity, which occurred in eight patients (17.8%). Among these patients, only one had pre-existing chronic kidney failure.    Conclusion: Colistin used in combination therapy may be effective and safe for treating nosocomial infections caused by multi-drug resistant gram-negative bacteria in pediatric patients, who often have high mortality rates and limited treatment options. What is Known: • Colistin is an antibacterial agent used in the treatment of infections caused by multidrug-resistant Gram-negative bacteria (MDR-GNB) and is associated with significant adverse effects such as nephrotoxicity. • The increasing prevalence of hospital-acquired infections has led to the expanded use of colistin in clinical practice. What is New: • The study demonstrates a high clinical and microbiological response rate to combination therapy with colistin in the treatment of infections caused by MDR-GNB. • The study highlights the importance of monitoring nephrotoxicity in pediatric patients receiving colistin, showing that these effects can be reversible after treatment cessation.

Genome analyses of colistin-resistant high-risk blaNDM-5 producing Klebsiella pneumoniae ST147 and Pseudomonas aeruginosa ST235 and ST357 in clinical settings

BACKGROUND

Colistin is a last-resort antibiotic used in extreme cases of multi-drug resistant (MDR) Gram-negative bacterial infections. Colistin resistance has increased in recent years and often goes undetected due to the inefficiency of predominantly used standard antibiotic susceptibility tests (AST). To address this challenge, we aimed to detect the prevalence of colistin resistance strains through both Vitek®2 and broth micro-dilution. We investigated 1748 blood, tracheal aspirate, and pleural fluid samples from the Intensive Care Unit (ICU), Neonatal Intensive Care Unit (NICU), and Tuberculosis and Respiratory Disease centre (TBRD) in an India hospital. Whole-genome sequencing (WGS) of extremely drug-resitant (XDR) and pan-drug resistant (PDR) strains revealed the resistance mechanisms through the Resistance Gene Identifier (RGI.v6.0.0) and Snippy.v4.6.0. Abricate.v1.0.1, PlasmidFinder.v2.1, MobileElementFinder.v1.0.3 etc. detected virulence factors, and mobile genetic elements associated to uncover the pathogenecity and the role of horizontal gene transfer (HGT).

RESULTS

This study reveals compelling insights into colistin resistance among global high-risk clinical isolates: Klebsiella pneumoniae ST147 (16/20), Pseudomonas aeruginosa ST235 (3/20), and ST357 (1/20). Vitek®2 found 6 colistin-resistant strains (minimum inhibitory concentrations, MIC = 4 μg/mL), while broth microdilution identified 48 (MIC = 32-128 μg/mL), adhering to CLSI guidelines. Despite the absence of mobile colistin resistance (mcr) genes, mechanisms underlying colistin resistance included mgrB deletion, phosphoethanolamine transferases arnT, eptB, ompA, and mutations in pmrB (T246A, R256G) and eptA (V50L, A135P, I138V, C27F) in K. pneumoniae. P. aeruginosa harbored phosphoethanolamine transferases basS/pmrb, basR, arnA, cprR, cprS, alongside pmrB (G362S), and parS (H398R) mutations. Both strains carried diverse clinically relevant antimicrobial resistance genes (ARGs), including plasmid-mediated blaNDM-5 (K. pneumoniae ST147) and chromosomally mediated blaNDM-1 (P. aeruginosa ST357).

CONCLUSION

The global surge in MDR, XDR and PDR bacteria necessitates last-resort antibiotics such as colistin. However, escalating resistance, particularly to colistin, presents a critical challenge. Inefficient colistin resistance detection methods, including Vitek2, alongside limited surveillance resources, accentuate the need for improved strategies. Whole-genome sequencing revealed alarming colistin resistance among K. pneumoniae and P. aeruginosa in an Indian hospital. The identification of XDR and PDR strains underscores urgency for enhanced surveillance and infection control. SNP analysis elucidated resistance mechanisms, highlighting the complexity of combatting resistance.

Restoring colistin sensitivity in colistin-resistant Salmonella and Escherichia coli: combinatorial use of berberine and EDTA with colistin

The appearance and prevalence of multidrug-resistance (MDR) Gram-negative bacteria (GNB) have limited our antibiotic capacity to control bacterial infections. The clinical efficacy of colistin (COL), considered as the "last resort" for treating GNB infections, has been severely hindered by its increased use as well as the emergence and prevalence of mobile colistin resistance (MCR)-mediated acquired drug resistance. Identifying promising compounds to restore antibiotic activity is becoming an effective strategy to alleviate the crisis of increasing MDR. We first demonstrated that the combination of berberine (BBR) and EDTA substantially restored COL sensitivity against COL-resistant Salmonella and Escherichia coli. Molecular docking indicated that BBR can interact with MCR-1 and the efflux pump system AcrAB-TolC, and BBR combined with EDTA downregulated the expression level of mcr-1 and tolC. Mechanically, BBR combined with EDTA could increase bacterial membrane damage, inhibit the function of multidrug efflux pump, and promote oxidative damage, thereby boosting the action of COL. In addition, transcriptome analysis found that the combination of BBR and EDTA can accelerate the tricarboxylic acid cycle, inhibit cationic antimicrobial peptide (CAMP) resistance, and attenuate Salmonella virulence. Notably, the combination of BBR and EDTA with COL significantly reduced the bacterial load in the liver and spleen of a mice model infected with Salmonella. Our findings revealed that BBR and EDTA can be used as adjuvants collectively with COL to synergistically reverse the COL resistance of bacteria.

IMPORTANCE

Colistin is last-resort antibiotic used to treat serious clinical infections caused by MDR bacterial pathogens. The recent emergence of transferable plasmid-mediated COL resistance gene mcr-1 has raised the specter of a rapid worldwide spread of COL resistance. Coupled with the fact of barren antibiotic development pipeline nowadays, a critical approach is to revitalize existing antibiotics using antibiotic adjuvants. Our research showed that berberine combined with EDTA effectively reversed COL resistance both in vivo and in vitro through multiple modes of action. The discovery of berberine in combination with EDTA as a new and safe COL adjuvant provides a therapeutic regimen for combating Gram-negative bacteria infections. Our findings provide a potential therapeutic option using existing antibiotics in combination with antibiotic adjuvants and address the prevalent infections caused by MDR Gram-negative pathogens worldwide.

Prevalence and molecular characterization of colistin resistance in Pseudomonas aeruginosa isolates: insights from a study in Ardabil hospitals

BACKGROUND

Pseudomonas aeruginosa is a common cause of nosocomial infections. However, the emergence of multidrug-resistant strains has complicated the treatment of P. aeruginosa infections. While polymyxins have been the mainstay for treatment, there is a global increase in resistance to these antibiotics. Therefore, our study aimed to determine the prevalence and molecular details of colistin resistance in P. aeruginosa clinical isolates collected between June 2019 and May 2023, as well as the genetic linkage of colistin-resistant P. aeruginosa isolates.

RESULTS

The resistance rate to colistin was 9% (n = 18) among P. aeruginosa isolates. All 18 colistin-resistant isolates were biofilm producers and carried genes associated with biofilm formation. Furthermore, the presence of genes encoding efflux pumps, TCSs, and outer membrane porin was observed in all colistin-resistant P. aeruginosa strains, while the mcr-1 gene was not detected. Amino acid substitutions were identified only in the PmrB protein of multidrug- and colistin-resistant strains. The expression levels of mexA, mexC, mexE, mexY, phoP, and pmrA genes in the 18 colistin-resistant P. aeruginosa strains were as follows: 88.8%, 94.4%, 11.1%, 83.3%, 83.3%, and 38.8%, respectively. Additionally, down-regulation of the oprD gene was observed in 44.4% of colistin-resistant P. aeruginosa strains.

CONCLUSION

This study reports the emergence of colistin resistance with various mechanisms among P. aeruginosa strains in Ardabil hospitals. We recommend avoiding unnecessary use of colistin to prevent potential future increases in colistin resistance.

Establishment and application of recombinase polymerase amplification combined with a lateral flow dipstick for the detection of mcr-1 in uncultured clinical samples

OBJECTIVES

The rapid dissemination of the mcr-1 gene via plasmid-mediated transfer has raised concerns regarding the efficacy of colistin as a last-resort treatment for multidrug-resistant Gram-negative bacterial infections. Current mcr-1 gene detection methods mainly focus on cultured bacteria, which is a complex and time-consuming process requiring skilled personnel, making it unsuitable for field analysis.

METHODS

A rapid detection technique combining recombinase polymerase amplification with a lateral flow dipstick targeting uncultured clinical samples was developed.

RESULTS

This new method targeting the mcr-1 gene region (23 232-23 642 bp, no. KP347127.1) achieved a low detection limit of 10 copies/μL. The whole process was carried out with high specificity and was completed within 20 min. The evaluation assay was conducted using 45 human faecal samples; 16 strains yielded a 98% accuracy, closely matching antimicrobial susceptibility outcomes.

CONCLUSIONS

The novel method integrates nucleic acid extraction, isothermal amplification, and a test assay, suggesting the potential for timely colistin resistance surveillance in frontline disease control and healthcare settings, supporting future prevention and clinical standardization efforts.

Ineffectiveness of colistin monotherapy in treating carbapenem-resistant Acinetobacter baumannii Pneumonia: A retrospective single-center cohort study

BACKGROUND

Acinetobacter baumannii, a common carbapenem-resistant gram-negative bacillus, usually causes nosocomial infections. Colistin has been used for carbapenem-resistant A. baumannii (CRAB) infections; however, only a few studies have evaluated colistin as a treatment option compared to appropriate controls. We investigated the effectiveness of colistin monotherapy in treating CRAB pneumonia compared to those treated without an active drug.

METHODS

Adult patients (≥ 18 years) with CRAB isolated from respiratory specimens were screened from September 2017 to August 2022. Only patients with pneumonia treated with colistin monotherapy (colistin group) were included and compared to those without any active antibiotics (no active antibiotics [NAA] group). The primary and secondary outcomes were 30-day all-cause mortality and acute kidney injury within 30 days. The inverse probability of the treatment-weighted Cox proportional hazard model was used to compare mortality between groups.

RESULTS

Among the 826 adult patients with CRAB in their respiratory specimens, 45 and 123 patients were included in the colistin and NAA groups, respectively. Most of the CRAB pneumonia (91.1%) cases were hospital-acquired pneumonia. The 30-day all-cause mortality rates in the colistin and NAA groups were 58.3% and 56.1%, respectively, and no difference was observed after adjustments (adjusted hazard ratio, 0.74; 95% CI, 0.47-1.17). The incidence of acute kidney injury was higher in the colistin group (65.3%) compared to the NAA group (39.0%) (P = 0.143).

CONCLUSIONS

Colistin monotherapy did not significantly improve treatment outcomes for CRAB pneumonia. The development and evaluation of new antimicrobials for CRAB pneumonia should be advocated in clinical practice.

Comparative effectiveness and mortality of colistin monotherapy versus colistin-fosfomycin combination therapy for the treatment of carbapenem-resistant Enterobacteriaceae (CRE) infections: A propensity score analysis

BACKGROUND

Carbapenem-resistant Enterobacteriaceae (CRE) infections pose a significant threat to global health due to limited treatment options and high mortality rates. Colistin-based regimens have emerged as a primary treatment approach, but the effectiveness and mortality outcomes of colistin monotherapy versus colistin-fosfomycin combination therapy remain uncertain. This study aims to compare the effectiveness and mortality of colistin monotherapy and colistin-fosfomycin combination therapy for CRE infections. Notably, our study is the first to undertake a comprehensive examination of the effectiveness and mortality outcomes between colistin monotherapy and colistin-fosfomycin combination therapy in the context of CRE infections.

METHODS

A retrospective cohort study was conducted using data from patients diagnosed with carbapenem-resistant Enterobacteriaceae (CRE) infections at Nakornping Hospital during 2015 to 2022. Inverse probability weighting (IPW) was employed to create balanced cohorts of patients receiving either colistin monotherapy or colistin-fosfomycin combination therapy. The primary outcome measure was treatment effectiveness, assessed by 30-day mortality. Secondary outcome measures included clinical response, mortality at the end of treatment, and microbiologic response. Univariate and multivariate logistic regression analysis were employed after applying propensity score weighting using inverse probability of weighting (IPW).

RESULTS

A total of 220 patients were included in the analysis, with 67 receiving colistin monotherapy and 153 receiving colistin-fosfomycin combination therapy. Propensity score weighting using IPW balanced the baseline characteristics between the two groups. The effectiveness of treatment, as measured by 30-day mortality, was not significantly different between the colistin monotherapy group and the colistin-fosfomycin combination therapy group (adjusted odds ratio [aOR] = 1.51, 95% confidence interval [CI]: 0.60-3.78, p = 0.383). Similarly, no significant difference was observed in the mortality at the end of treatment between the two groups (aOR = 1.26, 95% CI: 0.55-2.90, p = 0.576). The clinical response (aOR = 1.48, 95% CI: 0.61-3.59, p = 0.383) and microbiologic response (aOR = 0.66, 95% CI: 0.18-2.38, p = 0.527) were similar between the colistin monotherapy and colistin-fosfomycin combination therapy groups.

CONCLUSION

The propensity score analysis among 220 matched patients showed comparable treatment effectiveness and mortality between colistin monotherapy and colistin-fosfomycin combination therapy for CRE infections. These results suggest that colistin monotherapy may be as effective as combination therapy. More prospective randomized controlled trials are needed to confirm these findings and establish optimal CRE treatment strategies.

NhaA: A promising adjuvant target for colistin against resistant Escherichia coli

The emergence and widespread of multidrug-resistant Gram-negative bacteria have posed a severe threat to human health and environmental safety, escalating into a global medical crisis. Utilization of antibiotic adjuvants is a rapid approach to combat bacterial resistance effectively since the development of new antimicrobial agents is a formidable challenge. NhaA, driven by proton motive force, is a crucial secondary transporter on the cytoplasmic membrane of Escherichia coli. We found that 2-Aminoperimidine (2-AP), which is a specific inhibitor of NhaA, could enhance the activity of colistin against sensitive E. coli and reverse the resistance in mcr-1 positive E. coli. Mechanistic studies indicated that 2-AP induced dysfunction in cytoplasmic membrane through the suppression of NhaA, leading to metabolic inhibition and ultimately enhancing the sensitivity of E. coli to colistin. Moreover, 2-AP restored the efficacy of colistin against resistant E. coli in two animal infection models. Our findings reveal the potential of NhaA as a novel target for colistin adjuvants, providing new possibilities for the clinical application of colistin.

Clinical outcomes of colistin methanesulfonate sodium in correlation with pharmacokinetic parameters in critically ill patients with multi-drug resistant bacteria-mediated infection: A systematic review and meta-analysis

BACKGROUND

Colistin is a viable option for multidrug resistant gram-negative bacteria emerged from inappropriate antibiotic use. Nonetheless, suboptimal colistin concentrations and nephrotoxicity risks hinder its clinical use. Thus, the aim of this study is to investigate clinical outcomes in correlation with pharmacokinetic differences and infection types in critically ill patients on intravenous colistin methanesulfornate sodium (CMS).

METHODS

A systematic literature search of Embase, Google Scholars, and PubMed was performed to identify clinical trials evaluating pharmacokinetic parameters along with clinical outcomes of CMS treatment from inception to July 2023. The pooled analyses of clinical impact of CMS on nephrotoxicity, mortality, clinical cure, and colistin concentration at steady state (Css,avg) were performed. This study was registered in the PROSPERO (CRD 42023456120).

RESULTS

Total of 695 critically ill patients from 17 studies were included. The mortality was substantially lower in clinically cured patients (OR 0.05; 95% CI 0.02 - 0.14), whereas the mortality rate was statistically insignificant between nephrotoxic and non-nephrotoxic patients. Inter-patient variability of pharmacokinetic parameters of CMS and colistin was observed in critically ill patients. The standard mean differences of Css,avg were statistically insignificant between clinically cure and clinically failure groups (standard mean difference (SMD) -0.25; 95% CI -0.69 - 0.19) and between nephrotoxic and non-nephrotoxic groups (SMD 0.67; 95% CI -0.27-1.61). The clinical cure rate is substantially lower in pneumonia patients (OR 0.09; 95% CI 0.01 - 0.56), and pharmacokinetic parameters pertaining to microbiological cure were different among strains.

CONCLUSION

The mortality rate was substantially lower in clinically cured patients with CMS. However, no significant differences in Css,avg of colistin were examined to determine the impact of pharmacokinetic differences on clinical outcomes including mortality rate and nephrotoxicity risk. Nevertheless, the clinical cure rate is substantially lower in patients with respiratory infection than patients with urinary tract infection.

Enhancing effect of natural adjuvant, panduratin A, on antibacterial activity of colistin against multidrug-resistant Acinetobacter baumannii

Colistin- and carbapenem-resistant Acinetobacter baumannii is a serious multidrug resistant (MDR) bacterium in clinical settings. Discovery of new antibacterial drugs against MDR is facing multiple challenges in drug development. Combination of known antibiotics with a robust adjuvant might be an alternative effective strategy for MDR treatment. In the study herein, we report an antibiotic adjuvant activity of a natural compound panduratin A from fingerroot (Boesenbergia rotunda) as a potent adjuvant to colistin. The present study investigated the antibiotic adjuvant effect of panduratin A against 10 colistin- and carbapenem-resistant A. baumannii. Antibacterial activities were tested by broth microdilution method. Biofilm assay was used to determine the efficacy of panduratin A in biofilm formation inhibition on two representative strains Aci46 and Aci44. Genomic and transcriptomic analyses of colistin- and carbapenem-resistant A. baumannii strains were used to identify potential resistance and tolerance mechanism in the bacteria. Panduratin A-colistin combination showed an increased effect on antibacterial in the A. baumannii. However, panduratin A did not improve the antibacterial activity of imipenem. In addition, panduratin A improves anti-biofilm activity of colistin against Aci44 and Aci46, the colistin- and carbapenem-resistant A. baumannii. Panduratin A markedly enhances bactericidal and anti-biofilm activity of colistin against colistin- resistant A. baumannii. Based on genome comparisons, single nucleotide polymorphism (SNP) patterns in six genes encoding biofilm and lipid A biosynthesis were shared in Aci44 and Aci46. In Aci44, we identified a partial sequence of pmrB encoding a polymyxin resistant component PmrB, whereas a full length of pmrB was observed in Aci46. RNA-seq analyses of Aci44 revealed that panduratin A-colistin combination induced expression of ribosomal proteins and oxidative stress response proteins, whereas iron transporter and MFS-type transporter systems were suppressed. Panduratin A-colistin combination could promote intracellular reactive oxygen species (ROS) accumulation could lead to the cidal effect on colistin-resistant A. baumannii. Combination of panduratin A and colistin showed a significant increase in colistin efficacy against colistin- resistant A. baumannii in comparison of colistin alone. Genomic comparison between Aci44 and Aci46 showed mutations and SNPs that might affect different phenotypes. Additionally, based on RNA-Seq, panduratin A-colistin combination could lead to ROS production and accumulation. These findings confirmed the potency of panduratin as colistin adjuvant against multidrug resistant A. baumannii.

Characterization of NMCR-3, NMCR-4 and NMCR-5, three novel non-mobile colistin resistance determinants: Implications for MCR-3, MCR-7, and MCR-5 progenitors, respectively

In this study, the progenitors of MCR-3, MCR-7 and MCR-5, namely NMCR-3, NMCR-4 and NMCR-5, were firstly discovered and indicating Aeromonas was a natural reservoir for MCR-3 and MCR-7. Furthermore, different evolutionary models for MCR-3, MCR-7 and MCR-5 were proposed.

A challenging case of carbapenem resistant Klebsiella pneumoniae-related pyogenic liver abscess with capsular polysaccharide hyperproduction: a case report

BACKGROUND

Carbapenem-resistant Klebsiella pneumoniae (CRKP) infections are a major public health problem, necessitating the administration of polymyxin E (colistin) as a last-line antibiotic. Meanwhile, the mortality rate associated with colistin-resistant K. pneumoniae infections is seriously increasing. On the other hand, importance of administration of carbapenems in promoting colistin resistance in K. pneumoniae is unknown.

CASE PRESENTATION

We report a case of K. pneumoniae-related pyogenic liver abscess in which susceptible K. pneumoniae transformed into carbapenem- and colistin-resistant K. pneumoniae during treatment with imipenem. The case of pyogenic liver abscess was a 50-year-old man with diabetes and liver transplant who was admitted to Abu Ali Sina Hospital in Shiraz. The K. pneumoniae isolate responsible for community-acquired pyogenic liver abscess was isolated and identified. The K. pneumoniae isolate was sensitive to all tested antibiotics except ampicillin in the antimicrobial susceptibility test and was identified as a non-K1/K2 classical K. pneumoniae (cKp) strain. Multilocus sequence typing (MLST) identified the isolate as sequence type 54 (ST54). Based on the patient's request, he was discharged to continue treatment at another center. After two months, he was readmitted due to fever and progressive constitutional symptoms. During treatment with imipenem, the strain acquired blaOXA-48 and showed resistance to carbapenems and was identified as a multidrug resistant (MDR) strain. The minimum inhibitory concentration (MIC) test for colistin was performed by broth microdilution method and the strain was sensitive to colistin (MIC < 2 µg/mL). Meanwhile, on blood agar, the colonies had a sticky consistency and adhered to the culture medium (sticky mucoviscous colonies). Quantitative real-time PCR and biofilm formation assay revealed that the CRKP strain increased capsule wzi gene expression and produced slime in response to imipenem. Finally, K. pneumoniae-related pyogenic liver abscess with resistance to a wide range of antibiotics, including the last-line antibiotics colistin and tigecycline, led to sepsis and death.

CONCLUSIONS

Based on this information, can we have a theoretical hypothesis that imipenem is a promoter of resistance to carbapenems and colistin in K. pneumoniae? This needs more attention.

Clinical effectiveness of cefiderocol for the treatment of bloodstream infections due to carbapenem-resistant Acinetobacter baumannii during the COVID-19 era: a single center, observational study

BACKGROUND

We assessed the clinical effectiveness of cefiderocol (CFDC) in comparison with colistin (COL) for the treatment of carbapenem-resistant Acinetobacter baumannii (CRAB) bloodstream infections (BSI).

MATERIALS/METHODS

Retrospective cohort study including adults with CRAB-BSI. Outcomes were mortality, clinical cure and adverse events during therapy. The average treatment effect of CFDC compared to COL was weighted with the inverse-probability treatment weight (IPTW).

RESULTS

Overall, 104 patients were included (50 CFDC, 54 COL), median age 66.5 years, median Charlson Comorbidity Index 5, septic shock in 33.6% of patients. Primary BSI accounted for 43.3% of cases, followed by ventilator-associated pneumonia (VAP) (26%), catheter-related BSI (20.2%) and hospital-acquired pneumonia (HAP) (9.6%). Although not significantly, mortality at all time points was lower for CFDC than COL, while clinical cure was higher in CFDC than COL (66% vs. 44.4%, p = 0.027). Adverse events were more frequent in COL than CFDC-group (38.8% vs. 10%, p < 0.0001), primarily attributed to acute kidney injury (AKI) in the COL group. Patients with bacteremic HAP/VAP treated with CFDC had a significant lower 30-d mortality and higher clinical cure than COL (p = 0.008 and p = 0.0008, respectively). Increment of CCI (p = 0.005), ICU (p = 0.025), SARS-CoV2 (p = 0.006) and ECMO (p < 0.0001) were independently associated with 30-d mortality, while receiving CFDC was not associated with survival.

CONCLUSIONS

CFDC could represent an effective and safe treatment option for CRAB BSI, especially in patients with bacteremic HAP/VAP and frail patients where the risk of acute renal failure during therapy should be avoided.

An update on antibacterial AlkylGuanidino Ureas: Design of new derivatives, synergism with colistin and data analysis of the whole library

Antimicrobial resistance (AMR) represents one of the most challenging global Public Health issues, with an alarmingly increasing rate of attributable mortality. This scenario highlights the urgent need for innovative medicinal strategies showing activity on resistant isolates (especially, carbapenem-resistant Gram-negative bacteria, methicillin-resistant S. aureus, and vancomycin-resistant enterococci) yielding new approaches for the treatment of bacterial infections. We previously reported AlkylGuanidino Ureas (AGUs) with broad-spectrum antibacterial activity and a putative membrane-based mechanism of action. Herein, new tetra- and mono-guanidino derivatives were designed and synthesized to expand the structure-activity relationships (SARs) and, thereby, tested on the same panel of Gram-positive and Gram-negative bacteria. The membrane-active mechanism of selected compounds was then investigated through molecular dynamics (MD) on simulated bacterial membranes. In the end, the newly synthesized series, along with the whole library of compounds (more than 70) developed in the last decade, was tested in combination with subinhibitory concentrations of the last resort antibiotic colistin to assess putative synergistic or additive effects. Moreover, all the AGUs were subjected to cheminformatic and machine learning analyses to gain a deeper knowledge of the key features required for bioactivity.

In vitro activity of antibiotics potentially effective against difficult-to-treat strains of Gram-negative rods: retrospective study

Bacterial resistance surveillance is one of the main outputs of microbiological laboratories and its results are important part of antimicrobial stewardship (AMS). In this study, the susceptibility of specific bacteria to selected antimicrobial agents was tested. The susceptibility of 90 unique isolates of pathogens of critical priority obtained from clinically valid samples of ICU patients in 2017-2021 was tested. 50% of these fulfilled difficult-to-treat resistance (DTR) criteria and 50% were susceptible to all antibiotics included in the definition. 10 Enterobacterales strains met DTR criteria, and 2 (20%) were resistant to colistin (COL), 2 (20%) to cefiderocol (FCR), 7 (70%) to imipenem/cilastatin/relebactam (I/R), 3 (30%) to ceftazidime/avibactam (CAT) and 5 (50%) to fosfomycin (FOS). For Enterobacterales we also tested aztreonam/avibactam (AZA) for which there are no breakpoints yet. The highest MIC of AZA observed was 1 mg/l, MIC range in the susceptible cohort was 0.032-0.064 mg/l and in the DTR cohort (incl. class B beta-lactamase producers) it was 0.064-1 mg/l. Two (13.3%) isolates of Pseudomonas aeruginosa (15 DTR strains) were resistant to COL, 1 (6.7%) to FCR, 13 (86.7%) to I/R, 5 (33.3%) to CAT, and 5 (33.3%) to ceftolozane/tazobactam. All isolates of Acinetobacter baumannii with DTR were susceptible to COL and FCR, and at the same time resistant to I/R and ampicillin/sulbactam. New antimicrobial agents are not 100% effective against DTR. Therefore, it is necessary to perform susceptibility testing of these antibiotics, use the data for surveillance (including local surveillance) and conform to AMS standards.

Coli strains

BACKGROUND

The current understanding of acquired chromosomal colistin resistance mechanisms in Enterobacterales primarily involves the disruption of the upstream PmrAB and PhoPQ two-component system (TCS) control caused by mutations in the regulatory genes. Interestingly, previous studies have yielded conflicting results regarding the interaction of regulatory genes related to colistin resistance in Escherichia coli, specifically those surrounding PhoPQ and PmrAB TCS.

RESULTS

In our study, we focused on two clinical non-mcr colistin-resistant strains of E. coli, TSAREC02 and TSAREC03, to gain a better understanding of their resistance mechanisms. Upon analysis, we discovered that TSAREC02 had a deletion (Δ27-45) in MgrB, as well as substitutions (G206R, Y222H) in PmrB. On the other hand, TSAREC03 exhibited a long deletion (Δ84-224) in PhoP, along with substitutions (M1I, L14P, P178S, T235N) in PmrB. We employed recombinant DNA techniques to explore the interaction between the PhoPQ and PmrAB two-component systems (TCSs) and examine the impact of the mutated phoPQ and pmrB genes on the minimum inhibitory concentrations (MICs) of colistin. We observed significant changes in the expression of the pmrD gene, which encodes a connector protein regulated by the PhoPQ TCS, in the TSAREC02 wild-type (WT)-mgrB replacement mutant and the TSAREC03 WT-phoP replacement mutant, compared to their respective parental strains. However, the expressions of pmrB/pmrA, which reflect PmrAB TCS activity, and the colistin MICs remained unchanged. In contrast, the colistin MICs and pmrB/pmrA expression levels were significantly reduced in the pmrB deletion mutants from both TSAREC02 and TSAREC03, compared to their parental strains. Moreover, we were able to restore colistin resistance and the expressions of pmrB/pmrA by transforming a plasmid containing the parental mutated pmrB back into the TSAREC02 and TSAREC03 mutants, respectively.

CONCLUSION

While additional data from clinical E. coli isolates are necessary to validate whether our findings could be broadly applied to the E. coli population, our study illuminates distinct regulatory pathway interactions involving colistin resistance in E. coli compared to other species of Enterobacterales. The added information provided by our study contribute to a deeper understanding of the complex pathway interactions within Enterobacterales.

Ceftazidime-avibactam alone or in combination with Aztreonam versus Polymyxins in the management of carbapenem-Resistant Klebsiella pneumoniae nosocomial Infections (CAPRI study): a retrospective cohort study from South India

INTRODUCTION

Carbapenem-resistant Klebsiella pneumoniae (CRKP) infections commonly cause hospital-acquired infections. The study aimed to compare the outcomes of CRKP infections between patients receiving ceftazidime avibactam +/- aztreonam and polymyxins in a hospital setting with a high prevalence of New Delhi Metallo Beta Lactamase production.

METHODS

We conducted a retrospective cohort study from January 2020 to September 2022 in critically ill adult patients admitted to a non-COVID-19 medical intensive care unit with CRKP infection. The patients were followed up for a total of 30 days or death, whichever was later.

RESULTS

Of a total of 106 patients included in the study, 65 patients received polymyxins and 41 patients received ceftazidime-avibactam +/- aztreonam. Higher 30-day mortality was noted in the polymyxin group (56.9% vs. 29.2%, P = 0.005). The mean time to event (mortality) in ceftazidime-avibactam +/- aztreonam was 23.9 + 1.5 days which was significantly higher compared to polymyxins (17.9 + 1.2 days, p = 0.006). On Cox regression analysis, after adjusting for the covariates, the hazard ratio for time to event with the use of polymyxin was 2.02 (95% CI: 1.03-3.9).

CONCLUSION

Ceftazidime-avibactam + aztreonam is possibly associated with better clinical outcomes in patients infected with CRKP.

Colistin heteroresistance in Citrobacter freundii clinical isolates from Republic of Korea

We investigated colistin heteroresistance in Citrobacter freundii isolates from Korean hospitals. Using population analysis profiling (PAP), we detected colistin heteroresistance in 31.3% of isolates. Among these, ST217 was the most prevalent clone (58.5%), particularly within colistin-heteroresistant isolates (80.0%). Interestingly, the second most common clone, ST248, was not found in heteroresistant isolates. We identified amino acid changes in PhoQ, PmrA, and PmrB, along with mRNA overexpression in pmrB and arnD. Colistin monotherapy showed no efficacy, but a combination of colistin and ciprofloxacin successfully eradicated all five isolates, even at 0.5 × minimum inhibitory concentrations. This study underscores the high prevalence of colistin heteroresistance in C. freundii isolates, limiting the effectiveness of colistin monotherapy. Combining colistin with ciprofloxacin may offer a viable treatment option for C. freundii infections.

Comparison of in vitro synergy between polymyxin B or colistin in combination with 16 antimicrobial agents against multidrug-resistant Acinetobacter baumannii isolates

PURPOSES

This study determined the synergy of polymyxin B (POLB) and colistin (COL) with 16 other tested antimicrobial agents in the inhibition of multidrug-resistant Acinetobacter baumannii (MDR-AB).

METHODS

We used chequerboard assays to determine synergy between the drugs against 50 clinical MDR-AB from a tertiary hospital in the Zhejiang province in 2019, classifying combinations as either antagonistic, independent, additive, or synergistic. The efficacy of hit combinations which showed highest synergistic rate were confirmed using time-kill assays.

RESULTS

Both POLB and COL displayed similar bactericidal effects when used in combination with these 16 tested drugs. Antagonism was only observed for a few strains (2%) exposed to a combination of POLB and cefoperazone/sulbactam (CSL). A higher percentage of synergistic combinations with POLB and COL were observed with rifabutin (RFB; 90%/96%), rifampicin (RIF; 60%/78%) and rifapentine (RFP; 56%/76%). Time-kill assays also confirmed the synergistic effect of POLB and rifamycin class combinations. 1/2 MIC rifamycin exposure can achieve bacterial clearance when combined with 1/2 MIC POLB or COL.

CONCLUSION

Nearly no antagonism was observed when combining polymyxins with other drugs by both chequerboard and time-kill assays, suggesting that polymyxins may be effective in combination therapy. The combinations of POLB/COL with RFB, RIF, and RFP displayed neat synergy, with RFB showing the greatest effect.

Hyaluronan/B12-chitosan polyelectrolyte complex for oral colistin administration

Polyelectrolyte complexes (PECs) based on polysaccharides, including hyaluronic acid (HA) and chitosan (CS), are promising delivery systems for antimicrobial agents, including oral administration of the peptide antibiotic colistin (CT). Modification of CS with different targeting ligands to improve intestinal permeability is a suitable way to improve the oral bioavailability of polyelectrolyte particles. This study describes the procedure for obtaining CT-containing PECs based on HA and CS modified with cyanocobalamin (vitamin B12). In this case, vitamin B12 is used as a targeting ligand because it is absorbed in the ileum via specific transporter proteins. The resulting PECs had a hydrodynamic size of about 284 nm and a positive ζ-potential of about 26 mV; the encapsulation efficiency was 88.2 % and the CT content was 42.2 μg/mg. The developed systems provided a two-phase drug release: about 50 % of the CT was released in 0.5-1 h, and about 60 % of the antibiotic was cumulatively released in 5 h. The antimicrobial activity of encapsulated CT was maintained at the same level as the pure drug for at least 24 h (minimum inhibitory concentration against Pseudomonas aeruginosa was 2 μg/mL for both). In addition, the apparent permeability coefficient of CT in the PEC formulation was 2.4 × 10-6 cm/s. Thus, the incorporation of CT into HA- and vitamin B12-modified CS-based PECs can be considered as a simple and convenient method to improve the oral delivery of CT.

Novel method for determination of colistin sulfate in human plasma by high-performance liquid chromatography-tandem mass spectrometry and its clinical applications in critically ill patients

Colistin is a last-resort antibiotic used for treating infections caused by carbapenem-resistant Gram-negative bacteria, particularly in critically patients, nevertheless its therapeutic window is narrow, and requires monitoring. A determination method suitable for clinical detection is conducive to ensure its efficacy and safety of patients with severe infection. We developed and validated a concise and accurate high-performance liquid chromatography-tandem mass spectrometry method for the determination of colistin A and B in human plasma. We used a Kinetex C18 column (50 mm × 2.1 mm, 2.6 μm) with acetonitrile (containing 0.1% formic acid) as the protein precipitant and water (containing 0.2% formic acid and 5 mmol/L ammonium formate) - acetonitrile (containing 0.2% formic acid) as the gradient elution. The calibration curves were linear over concentration ranges of 0.06-4.00 μg/mL (colistin A) and 0.1-7.0 μg/mL (colistin B). The precision, accuracy, matrix effect, extraction recovery, and stability were all validated. This method was applied to the therapeutic drug monitoring for 50 critically ill patients. The trough, peak, and average steady-state concentrations of these patients were 0.8 ± 0.4, 1.4 ± 0.5, and 1.0 ± 0.4 μg/mL, respectively. And the concentrations of colistin in human plasma were closely related to the patient's renal function.

A novel F type plasmid encoding mcr-10 in a clinical Enterobacter ludwigii strain from a tertiary hospital in the Czech Republic

OBJECTIVE

Here we describe a novel IncFIA plasmid harbouring mcr-10 gene in a clinical Enterobacter ludwigii strain isolated at the University Hospital in Pilsen in the Czech Republic.

METHODS

The strain was subjected to antibiotic susceptibility testing. Whole genome sequencing was performed using Illumina for short-read sequencing and Oxford Nanopore Technologies for long-read sequencing followed by hybrid assembly. The resulting genome was used to detect species using average nucleotide identity, resistance genes, plasmid replicon and MLST (using centre for genomic epidemiology databases; ResFinder, PlasmidFinder and MLST, respectively) and virulence genes using VFDB.

RESULTS

Τhe strain showed susceptibility against tetracycline, cefuroxime and chloramphenicol, and it was susceptible to the second and third generation of cephalosporins, carbapenems and colistin. Genome analysis identified the strain as E. ludwigii sequence type ST20 and located the mcr-10 gene on an IncFIA (HI1)/IncFII (Yp) plasmid (pI9455333_MCR10; 129 863 bp). Upon blasting the nucleotide sequence of pI9455333_MCR10 against the NCBI database, no similar plasmid sequence was detected, implying a novel plasmid structure. Nevertheless, it showed a partial similarity with pRHBSTW-00123_3 and FDAARGOS 1432, which were detected in Enterobacter cloacae complex (ECC) strains in wastewater samples in 2017 in UK and in 2021 in the United States, respectively, and pEC81-mcr, which was detected in a clinical Escherichia coli strain in 2020 in China. Moreover, I9455333cz genome carried virulence genes coding for curli fibers, fimbrial adherence determinants, siderophore aerobactin, iron uptake proteins and regulators of sigma factor.

CONCLUSION

In conclusion, we identified a novel IncF plasmid harbouring mcr-10 gene in a clinical Enterobacter ludwigii strain. To our knowledge, this is the first clinical report of mcr-10 in the Czech Republic.

Sub-inhibitory concentrations of colistin and imipenem impact the expression of biofilm-associated genes in Acinetobacter baumannii

Acinetobacter baumannii is an opportunistic pathogen that is responsible for nosocomial infections. Imipenem and colistin are drugs that are commonly used to treat severe infections caused by A. baumannii, such as sepsis, ventilator-associated pneumonia, and bacteremia. However, some strains of A. baumannii have become resistant to these drugs, which is a concern for public health. Biofilms produced by A. baumannii increase their resistance to antibiotics and the cells within the inner layers of biofilm are exposed to sub-inhibitory concentrations (sub-MICs) of antibiotics. There is limited information available regarding how the genes of A. baumannii are linked to biofilm formation when the bacteria are exposed to sub-MICs of imipenem and colistin. Thus, this study's objective was to explore this relationship by examining the genes involved in biofilm formation in A. baumannii when exposed to low levels of imipenem and colistin. The study found that exposing an isolate of A. baumannii to low levels of these drugs caused changes in their drug susceptibility pattern. The relative gene expression profiles of the biofilm-associated genes exhibited a change in their expression profile during short-term and long-term exposure. This study highlights the potential consequences of overuse and misuse of antibiotics, which can help bacteria become resistant to these drugs.

Antimicrobial photodynamic effect of the photosensitizer riboflavin, alone and in combination with colistin, against pandrug-resistant Pseudomonas aeruginosa clinical isolates

INTRODUCTION

Development of multi-, extensively-, and pandrug-resistant (MDR, XDR, and PDR) strains of Pseudomonas aeruginosa remains a major problem in medical care. The present study evaluated the effect of antimicrobial photodynamic therapy (aPDT) as a monotherapy and in combination with colistin against P. aeruginosa isolates.

METHODS

Two P. aeruginosa isolates recovered from patients with respiratory tract infections were examined in this study. Minimum inhibitory concentration (MIC) of colistin was determined by the colistin broth disk elution (CBDE) and the reference broth microdilution (rBMD) methods. aPDT was performed using the photosensitizer (Ps) riboflavin at several concentrations and a light-emitting diode (LED) emitting blue light for different irradiation times with or without colistin at 1/2 × MIC concentration.

RESULTS

Both PA1 and PA2 isolates were identified as colistin-resistant P. aeruginosa with a MIC ≥4 μg/mL by the CBDE and MICs of 512 μg/mL and 256 μg/mL, respectively, by the rBMD. In aPDT, neither riboflavin nor LED light alone had antibacterial effects. The values of colony forming units per milliliter (CFU/mL) in both isolates were significantly reduced by LED + Ps treatments in a time-dependent manner (LED irradiation time) and dose-dependent manner (Ps concentration). In comparison with control, treatment with Ps (50 μM) + LED (120 s) and Ps (100 μM) + LED (120 s) resulted in 0.27 log10 CFU/mL and 0.43 log10 CFU/mL reductions in PA1, and 0.28 log10 CFU/mL and 0.34 log10 CFU/mL reductions in PA2, respectively, (P < 0.01). The best results were obtained after the combination of aPDT followed by colistin, which increased bacterial reduction, resulting in a 0.41-0.7 log10 CFU/mL reduction for PA1 and 0.35-0.83 log10 CFU/mL reduction for PA2 (P = 0.001).

CONCLUSIONS

This study suggests the potential implications of aPDT in combination with antibiotics, such as colistin for treatment of difficult-to-treat P. aeruginosa infections.

The use of combination therapy for the improvement of colistin activity against bacterial biofilm

Colistin is used as a last resort for the management of infections caused by multi-drug resistant (MDR) bacteria. However, the use of this antibiotic could lead to different side effects, such as nephrotoxicity, in most patients, and the high prevalence of colistin-resistant strains restricts the use of colistin in the clinical setting. Additionally, colistin could induce resistance through the increased formation of biofilm; biofilm-embedded cells are highly resistant to antibiotics, and as with other antibiotics, colistin is impaired by bacteria in the biofilm community. In this regard, the researchers used combination therapy for the enhancement of colistin activity against bacterial biofilm, especially MDR bacteria. Different antibacterial agents, such as antimicrobial peptides, bacteriophages, natural compounds, antibiotics from different families, N-acetylcysteine, and quorum-sensing inhibitors, showed promising results when combined with colistin. Additionally, the use of different drug platforms could also boost the efficacy of this antibiotic against biofilm. The mentioned colistin-based combination therapy not only could suppress the formation of biofilm but also could destroy the established biofilm. These kinds of treatments also avoided the emergence of colistin-resistant subpopulations, reduced the required dosage of colistin for inhibition of biofilm, and finally enhanced the dosage of this antibiotic at the site of infection. However, the exact interaction of colistin with other antibacterial agents has not been elucidated yet; therefore, further studies are required to identify the precise mechanism underlying the efficient removal of biofilms by colistin-based combination therapy.

Extensively drug-resistant Enterobacter ludwigii co-harbouring MCR-9 and a multicopy of blaIMP-1 in South Korea

In this study, we describe an Enterobacter ludwigii clinical isolate that is resistant to both carbapenems and colistin in South Korea. Antimicrobial susceptibility testing revealed that E. ludwigii CRE2104-31 was non-susceptible to all tested antibiotics except fosfomycin. Whole genome sequencing identified a 323-kbp IncHI2 plasmid, pCRE2104-31a, that was co-harbouring mobile colistin resistance (mcr)-9.1 and blaIMP-1. In comparison with other full plasmids, pCRE2104-31a exhibited the closest similarity to a plasmid from the Klebsiella pneumoniae strain CNR48 from France, with 19.9% query coverage and 99% identity. Notably, we observed five tandem repeats of blaIMP-1 and aac(6')-Il genes, accompanied by multiple attCs within a class I integron on the Tn402-like transposon. The unit of blaIMP-1-attC-aac(6')-Il-attC might have accumulated due to multiple convergent events. In addition to mcr-9.1 and blaIMP-1, various other antibiotic resistance-associated genes were identified in the plasmid, as follows: blaTEM-1B, aph(3')-I, aph(3')-Ia, aac(6')-Il, aac(6')-IIc, aac(6')-IIa, aph(6)-Id, aph(3'')-Ib, aadA2b, aac(6')-Ib3, sul, dfrA19, qnrB2, aac(6')-Ib-cr, ere(A), and qacE. A conjugation assay showed that the mcr-9.1/blaIMP-1-co-bearing plasmid was self-transmissible to E. coli J53. However, colistin and carbapenem resistance could not be transferred to E. coli due to high incompatibility. The convergence of mcr and carbapenemase genes is thought to be host-dependent among Enterobacteriaceae. The emergence of extensively drug-resistant E. ludwigii co-harbouring MCR-9.1 and a multicopy of blaIMP-1 would pose a significant threat within the compatible Enterobacteriaceae.

In vitro activity of the newly approved antimicrobial agent Cefiderocol against Carbapenem resistant Gram negative clinical isolates

INTRODUCTION

Carbapenem resistant Gram negative bacteria have emerged as priority pathogens in recent years. Cefiderocol is a siderophore cephalosporin licensed in 2019 with claimed activity against ESBL producing and carbapenem resistant bacteria with much better safety margin compared to colistin. The present study was undertaken to assess the in vitro activity of cefiderocol against carbapenem resistant clinical isolates, compared to some select antimicrobial agents including colistin.

MATERIALS AND METHODS

Seventy-seven isolates of Gram negative bacteria belonging to the three commonly encountered groups of Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter spp were included. Susceptibility testing for Cefiderocol was determined by Kirby-Bauer's disk diffusion technique as per CLSI guidelines using Cefiderocol disc (30 μg). Sensitivity for the other agents were determined using automated system.

RESULTS

Of the 77 isolates, 58.4% belonged to Enterobacterales, followed by P.aeruginosa (27.3%) and Acinetobacter spp (14.3%). Three out of 45 Enterobacterales isolates, one out of 21 P.aeruginosa and none in the Acinetobacter group were found resistant to cefiderocol. All the isolates were intermediate sensitive (I) for colistin since the "susceptible" interpretive category has been eliminated. Tigecycline showed good activity (80.0% sensitive) against Enterobacterales followed by aztreonam (71.1% sensitive).

CONCLUSION

Cefiderocol is not yet available in India and our study is possibly the second one from this country demonstrating in vitro resistance to this important antimicrobial agent. However, with a relatively better safety profile compared to colistin, cefiderocol can be an important agent to combat these highly resistant pathogens.

Assessment of in vitro colistin susceptibility of carbapenem-resistant clinical Gram-negative bacterial isolates using four commercially available systems & Whole-genome sequencing: A diagnostic accuracy study

AIM

To analyze the diagnostic utility of commercially available platforms and Whole-genome sequencing (WGS) for accurate determination of colistin susceptibility test results.

MATERIAL & METHODS

An exploratory diagnostic accuracy study was conducted in which sixty carbapenem-resistant Gram-negative bacteria were subjected to identification and AST using MALDI-TOF MS & MicroScan walkaway 96 Plus. Additional AST was performed using the BD Phoenix system and Mikrolatest colistin kit. The test isolates were subjected to Vitek-2 and WGS at CRL, Bengaluru.

RESULTS

There was no statistically significant agreement between the colistin susceptibility results obtained by WGS, with those of commercial phenotypic platforms. The MicroScan 96 Plus had the highest sensitivity (31 %) & NPV (77 %), and the BD Phoenix system had the highest specificity (97 %) and PPV (50 %), respectively, for determining colistin resistance.

CONCLUSION

The utility of WGS as a tool in AMR surveillance and validation of phenotypic AST methods should be explored further.

In vitro antimicrobial susceptibility data of global meropenem-resistant Acinetobacter baumannii isolates causing pneumonia: Data from the Antimicrobial Testing Leadership and Surveillance Program, 2014-2021, and re-estimations of susceptibility breakpoints and appropriate dosages of important antibiotics for pneumonia treatment

OBJECTIVES

To evaluate the susceptibility of globally pneumonia-causing meropenem-resistant (MEM-R) Acinetobacter baumannii isolates against important antibiotics and estimate appropriate dosages of indicated antibiotics.

METHODS

We extracted the 2014-2021 Antimicrobial Testing of Leadership Surveillance database regarding the susceptibility of MEM-R A. baumannii isolates causing pneumonia against important antibiotics. The susceptibility and carbapenemase-encoding gene (CPEG) data of pneumonia-causing MEM-R A. baumannii isolates from patients hospitalized in intensive care units of five major regions were analyzed. The susceptibility breakpoints (SBP) recommended by the Clinical and Laboratory Standards Institute (CLSI) in 2022, other necessary criteria [SBP of MIC for colistin, 2 mg/L, in the CLSI 2018; and cefoperazone-sulbactam (CFP-SUL), 16 mg/L], and the pharmacokinetic and pharmacodynamic data of indicated antibiotics were employed.

RESULTS

Applying the aforementioned criteria, we observed the susceptible rates of colistin, minocycline, and CFP-SUL against the pneumonia-causing MEM-R A. baumannii isolates globally (n = 2905) were 93.2%, 69.1%, and 26.3%, respectively. Minocycline was significantly more active in vitro (MIC ≤4 mg/L) against the pneumonia-causing MEM-R A. baumannii isolates collected from North and South America compared to those from other regions (>90% vs. 58-72%). Additionally, blaOXA-23 and blaOXA-72 were the predominant CPEG in pneumonia-causing MEM-R A. baumannii isolates.

CONCLUSIONS

After deliberative estimations, dosages of 200 mg minocycline intravenously every 12 h (SBP, 8 mg/L), 100 mg tigecycline intravenously every 12 h (SBP, 1 mg/L), and 160 mg nebulized colistin methanesulphonate every 8 h (SBP, 2 mg/L) are needed for the effective treatment of pneumonia-causing MEM-R A. baumannii isolates.

Induction of proteome changes involved in the cloning of mcr-1 and mcr-2 genes in Escherichia coli DH5-α strain to evaluate colistin resistance

OBJECTIVES

Plasmid genes, termed mobile colistin resistance-1 (mcr-1) and mobile colistin resistance-2 (mcr-2), are associated with resistance to colistin in Escherichia coli (E. coli). These mcr genes result in a range of protein modifications contributing to colistin resistance. This study aims to discern the proteomic characteristics of E. coli-carrying mcr-1 and mcr-2 genes. Furthermore, it evaluates the expression levels of various proteins under different conditions (with and without colistin).

METHODS

Plasmid extraction was performed using an alkaline lysis-based plasmid extraction kit, whereas polymerase chain reaction was used to detect the presence of mcr-1 and mcr-2 plasmids. The E. coli DH5α strain served as the competent cell for accepting and transforming mcr-1 and mcr-2 plasmids. We assessed proteomic alterations in the E. coli DH5α strain both with and without colistin in the growth medium. Proteomic data were analysed using mass spectrometry.

RESULTS

The findings revealed significant protein changes in the E. coli DH5α strain following cloning of mcr-1 and mcr-2 plasmids. Of the 20 proteins in the DH5α strain, expression in 8 was suppressed following transformation. In the presence of colistin in the culture medium, 39 new proteins were expressed following transformation with mcr-1 and mcr-2 plasmids. The proteins with altered expression play various roles.

CONCLUSION

The results of this study highlight numerous protein alterations in E. coli resulting from mcr-1 and mcr-2-mediated resistance to colistin. This understanding can shed light on the resistance mechanism. Additionally, the proteomic variations observed in the presence and absence of colistin might indicate potential adverse effects of indiscriminate antibiotic exposure on treatment efficacy and heightened pathogenicity of microorganisms.

Comparative evaluation of Vitek®2 and broth microdilution method for colistin susceptibility testing of Gram-negative isolates from intensive care unit in a tertiary care hospital

INTRODUCTION

Colistin is the last resort treatment against resistant Gram-negative bacteria, necessitating reliable and rapid means for sensitivity testing of colistin. Automated systems like VITEK®2 are adopted to determine the minimum inhibitory concentration (MIC) due to easy usage. Broth microdilution (BMD) for colistin MIC was suggested by EUCAST and CLSI.

OBJECTIVE

To compare and evaluate colistin MIC by BMD and VITEK®2 against Gram-negative organisms from the ICU in a tertiary care hospital.

METHOD

Clinically significant organisms isolated from ICU patients were included. MIC was determined using BMD and VITEK®2. Very major error (VME), major error (ME), essential agreement (EA), categorical agreement (CA), positive predictive value (PPV), negative predictive value (NPV), sensitivity, and specificity were analysed.

RESULT

533 isolates were obtained from blood (435,81.60%), respiratory samples (57,10.70%), pus and exudates (20,3.80%), urine (18,3.40%), and CSF (3,0.60%). The Enterobacterales were K. pneumoniae (185,34.70%) E. coli (73,13.70%) and E. cloacae (26,4.90%) while non-fermenters were A. baumannii (209,39.20%) and P. aeruginosa (40,7.50%). The VITEK®2 sensitivity was >99%; specificity ranged from 14.28 to 52.94%. PPV was 93.81% while NPV was 93.75%. VME ranged from 47 to 100% between isolates. ME was up to 20%. The highest VME was obtained in E. coli (100%). The total EA and CA observed were 68.5% and 99.79% respectively.

CONCLUSION

Automated system VITEK®2 failed to detect the resistance in 32 (60%) isolates. The obtained VME and ME values were >3%, which is unacceptable as per the standard guidelines. EA of ≥90% wasn't obtained. Sensitivity for VITEK®2 was >99%, but had low specificity (14.28%). Hence, VITEK®2 is not reliable for colistin susceptibility testing.

Co-transfer of IncFII/IncFIB and IncFII plasmids mediated by IS26 facilitates the transmission of mcr-8.1 and tmexCD1-toprJ1

PURPOSE

This study aimed to characterise the whole-genome structure of two clinical Klebsiella pneumoniae strains co-harbouring mcr-8.1 and tmexCD1-toprJ1, both resistant to colistin and tigecycline.

METHODS

K. pneumoniae strains TGC-02 (ST656) and TGC-05 (ST273) were isolated from urine samples of different patients hospitalised at separate times in 2021. Characterisation involved antimicrobial susceptibility testing (AST), conjugation assays, whole-genome sequencing (WGS), and bioinformatics analysis. Comparative genomic analysis was conducted on mcr-8.1-carrying and tmexCD1-toprJ1-carrying plasmids.

RESULTS

Both K. pneumoniae isolates displayed a multidrug-resistant phenotype, exhibiting resistance or reduced susceptibility to ampicillin, ampicillin/sulbactam, cefazolin, aztreonam, amikacin, gentamicin, tobramycin, ciprofloxacin, levofloxacin, nitrofurantoin, trimethoprim/sulfamethoxazole, apramycin, tigecycline and colistin. WGS analysis revealed that clinical strain TGC-02 carried the TmexCD1-toprJ1 gene on a 200-Kb IncFII/IncFIB-type plasmid, while mcr-8 was situated on a 146-Kb IncFII-type plasmid. In clinical strain TGC-05, TmexCD1-toprJ1 was found on a 300-Kb IncFIB/IncHI1B/IncR-type plasmid, and mcr-8 was identified on a 137-Kb IncFII/IncFIA-type plasmid. Conjugation experiments assessed the transferability of these plasmids. While transconjugants were not obtained for TGC-05 despite multiple screening with tigecycline or colistin, pTGC-02-tmex and pTGC-02-mcr8 from clinical K. pneumoniae TGC-02 demonstrated self-transferability through conjugation. Notably, the rearrangement of pTGC-02-tmex and pTGC-02-mcr8 via IS26-based homologous recombination was observed. Moreover, the conjugative and fusion plasmids of the transconjugant co-harboured the tmexCD1-toprJ1 gene cluster and mcr-8.1, potentially resulting from IS26-based homologous recombination.

CONCLUSION

The emergence of colistin- and tigecycline-resistant K. pneumoniae strains is concerning, and effective surveillance measures should be implemented to prevent further dissemination.

Colistin monotherapy or combination for the treatment of bloodstream infection caused by Klebsiella pneumoniae: a systematic review and meta-analysis

BACKGROUND

Bloodstream infection of Klebsiella pneumoniae (BSI-KP) were associated with increased mortality. Klebsiella pneumoniae was tested to susceptible to colistin by E-test and broth microdilution method in clinical laboratory. This study aimed to assess the efficacy of colistin versus tigecycline, carbapenem monotherapy and combination in the treatment of BSI-KP.

METHODS

Electronic databases such as PubMed, Web of Science and Embase were searched. The last search was in November 24th, 2022, addressing the colistin, carbapenems and tigecycline monotherapy and combination treatments in patients with BSI-KP. The primary outcomes were 30-day or 28-day mortality. OR where available with 95% CI were pooled in random-effects meta-analysis.

RESULTS

Following the outlined search strategy, a total of 658 articles were identified from the initial database searching. Six studies, 17 comparisons were included. However, they all were observational design, lacking high-quality randomized controlled trials (RCTs). Moderate or low-quality evidences suggested that colistin monotherapy was associated with an OR = 1.35 (95% CI = 0.62-2.97, P = 0.45, Tau2 = 0.00, I2 = 0%) compared with tigecycline monotherapy, OR = 0.81 (95% CI = 0.27-2.45, P = 0.71, Tau2 = 0.00, I2 = 0%) compared with carbapenem monotherapy. Compared with combination with tigecycline or carbapenem, Colistin monotherapy resulted in OR of 3.07 (95% CI = 1.34-7.04, P = 0.008, Tau2 = 0.00, I2 = 0%) and 0.98 (95%CI = 0.29-3.31, P = 0.98, Tau2 = 0.00, I2 = 0% ), respectively.

CONCLUSIONS

Colistin, carbapenem and tigecycline monotherapy showed similar treatment effects in patients who suffered from BSI-KP. Compared with colistin monotherapy, colistin combined tigecycline therapy might play the synergism effects.

TRIAL REGISTRATION

retrospectively registered.

Low prevalence of mcr-1 in Escherichia coli from food-producing animals and food products in China

BACKGROUND

mcr-1-positive Escherichia coli has emerged as a significant threat to human health, veterinary health, and food safety in recent years. After the prohibition of colistin as a feed additive in animal husbandry in China, a noticeable reduction in both colistin resistance and the prevalence of mcr-1 was observed in E. coli from animals and humans.

OBJECTIVES

To assess the prevalence of the colistin resistance gene mcr-1 and characterize its genetic context in E. coli strains derived from fecal and meat samples from food-producing animals in China.

METHODS

A total of 1,353 fecal samples and 836 food samples were collected between 2019 and 2020 in China. E. coli isolates were identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and their susceptibility to colistin were determined using the broth microdilution method. The colistin-resistant E. coli isolates were screened for the presence of mcr by PCR analysis and sequencing. The minimal inhibitory concentrations (MICs) of 15 antimicrobial agents against the mcr-1-positive strains were further tested using the agar dilution method, conjugation assays were performed, and whole genome sequencing was performed using Illumina HiSeq.

RESULTS

In total, 1,403 E. coli strains were isolated. Thirteen isolates from chicken meat (n = 7), chickens (n = 3), and pigs (n = 3) were resistant to colistin with MIC values of 4 to 16 mg/L, and carried mcr-1. All mcr-1-positive strains, except for isolate AH20PE105, contained multiple resistance genes and exhibited multidrug-resistant phenotypes. They belonged to 10 sequence types (STs), including a novel ST (ST14521). mcr-1 was located on IncI2 (n = 9), IncX4 (n = 2), and IncHI2 (n = 2) plasmids, which were highly similar to other mcr-1-carrying plasmids sharing the same incompatibility type. Seven mcr-1-carrying plasmids could be successfully conjugally transferred to E. coli C600.

CONCLUSIONS

While the low prevalence of mcr-1 (0.93%) identified in this study may not immediately seem alarming, the very emergence of this gene merits attention given its implications for colistin resistance and public health. Hence, ongoing surveillance of mcr-1 in E. coli remains crucial.

Synergistic effects of nano curcumin mediated photodynamic inactivation and nano-silver@colistin against Pseudomonas aeruginosa biofilms

BACKGROUND

Patients with burn injuries colonized by multidrug-resistant Pseudomonas aeruginosa face increased mortality risk. The efficacy of colistin, a last-resort treatment, is declining as resistance levels rise. P. aeruginosa's robust biofilm exacerbates antibiotic resistance. Photodynamic Inactivation (PDI) shows promise in fighting biofilm.

MATERIALS AND METHODS

Nano curcumin (nCur) particles were synthesized, and their chemical characteristics were determined using zeta potential (ZP), dynamic light scattering analysis (DLS), energy-dispersive X-ray (EDX) analysis, and fourier transform infrared (FTIR). We conducted an MTT assay to assess the cytotoxicity of nCur-mediated PDI in combination with nanosilver colistin. The fractional biofilm inhibitory concentration (FBIC) of two P. aeruginosa clinical isolates and P. aeruginosa ATCC 27853 during nCur-mediated PDI@AgNPs@CL was determined using a 3-dimensional (3-D) checkerboard assay. To study the effect of nCur-mediated PDI@AgNPs@CL on lasI, lasR, rhlI, rhlR, pelA, and pslA gene expression, Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was conducted at each isolate's FBIC. The impact of treatments was also investigated using scanning electron microscopy (SEM).

RESULTS

The ZP and mean DLS values of the nCur were 10.3 mV and 402.6 ± 24.6 nm, respectively. The distinct functional groups of nCur corresponded with the peaks of FTIR absorption. Moreover, the EDX analysis showed the ratios of different metals in nCur. Cell viability percentages of nCur-mediated PDI@AgNPs@CL at FBIC concentrations of clinical isolates Nos. 30, 354, and P. aeruginosa ATCC 27853 were 91.36 %, 83.20 %, and 92.48 %, respectively. nCur-mediated PDI@AgNPs@CL treatment showed synergistic effects in clinical isolates and P. aeruginosa ATCC 27853 in a 3-D checkerboard assay. All six of the investigated genes showed down-regulation after nCur-mediated PDI@AgNPs@CL treatment. The most suppressed gene during nCur-mediated PDI@AgNPs@CL treatment was the rhlR gene (-11.9-fold) of P. aeruginosa ATCC 27853. The SEM micrographs further proved the connecting cement reduction and biofilm mass mitigation following nCur-mediated PDI@AgNPs@CL treatments.

CONCLUSIONS

The combined effect of nCur-mediated PDI and AgNPs@CL synergistically reduce the formation of biofilm in P. aeruginosa. This may be attributable to the suppression of the genes responsible for regulating the production of biofilms.

Battle of polymyxin induced nephrotoxicity: Polymyxin B versus colistin

OBJECTIVES

Nephrotoxicity is the most serious and common adverse effect that limits the use of polymyxins. This study compared polymyxin E (colistin) and polymyxin B regarding drug-related nephrotoxicity.

METHODS

This study was conducted as a retrospective cohort study in a university hospital between January 2020 and July 2022. Patients older than 18 years and who received colistin or polymyxin B were identified using electronic hospital records. Kidney disease improving global outcome criteria were used for assessing nephrotoxicity.

RESULTS

A total of 190 patients, 95 in both groups, were evaluated. The incidence of acute kidney injury during the treatment was higher in the colistin group [52.6% (n = 50) and 34.7% (n = 33), P = 0.013]. In patients who were exposed to high-dose, the rate of nephrotoxicity was higher in patients receiving colistin [25% (n = 3) vs. 76.9% (n = 10); P = 0.017]. Nephrotoxicity was reversible in 64.4% (n = 38) of patients and the reversibility rate was similar (70% and 52.6% for colistin and polymyxin; P = 0.248). In the multivariable analysis, colistin treatment [odds ratio (OR): 3.882, 95% confidence interval (95% CI) = (1.829-8.241)], concomitant vasopressor use (OR = 2.08, CI: 1.036-4.179), and age (OR=1.036, CI: 1.014-1.058) were found to be independent markers of nephrotoxicity.

CONCLUSION

Nephrotoxicity was more common in patients receiving high-dose colistin than polymyxin B. Therefore, the use of appropriate doses of colistin is important in terms of preventing nephrotoxicity. In addition, advancing age and concomitant use of vasopressors contribute to polymyxin-related nephrotoxicity.

Roles of crrAB two-component regulatory system in Klebsiella pneumoniae: growth yield, survival in initial colistin treatment stage, and virulence

OBJECTIVES

Alternation of the colistin resistance-regulating two-component regulatory system (crrAB) is a colistin-resistance mechanism in Klebsiella pneumoniae (K. pneumoniae), but its role in bacteria is not fully understood.

METHODS

Twelve colistin-susceptible K. pneumoniae clinical isolates were included in this study: six crrAB-positive and six crrAB-negative. We deleted the crrAB genes from two crrAB-positive isolates and complemented them. We measured the growth yields by determining growth curves in lysogeny broth and minimal media with or without Fe2+. In vitro selection rates for colistin resistance were determined by exposure to colistin, and survival rates against high concentrations of colistin (20 mg/L) at the early stage of growth (20 min) were investigated. Virulence was determined using a serum bactericidal assay and Galleria mellonella larval infection.

RESULTS

The presence of crrAB was not associated with colistin resistance and did not increase the in vitro selection rate of colistin resistance after exposure. The growth yield of crrAB-positive isolates was higher in lysogeny broth media and increased when Fe2+ was added to minimal media. The crrAB-positive isolates showed higher survival rates in the early stages of exposure to high colistin concentrations. Decreased serum resistance was identified in the crrAB-deleted mutants. More G. mellonella larvae survived when infected by crrAB-deleted mutants, and higher survival rates of bacteria were identified within the larvae infected with wild-type than crrAB-deletant isolates.

CONCLUSION

Through rapid response to external signals, crrAB would provide advantages for K. pneumoniae survival by increasing the final growth yield and initial survival against colistin treatment. This may partly contribute to the bacterial virulence.

coli harboring carbapenem and colistin-resistant genes from poultry farms in Egypt

Background

eEscherichia coli (E. coli) bacteria that produce extended spectrum beta-lactamase (ESBL) is associated with a high prevalence of human illnesses worldwide. The emergence of resistance to carbapenem and colistin compounds poses further challenges to the treatment options for these illnesses. This study aimed to evaluate the phenotypic and genotypic pattern of resistance to carbapenem and colistin in ESBL-producing E. coli. Escherichia coli isolates collected from the respiratory tract of chickens in El-Sharkia government, Egypt.

Methods

A total of 250 lung samples were collected from 50 poultry farms. These samples were then subjected to isolation, identification, and serotyping of E. coli. The presence of antimicrobial resistance was identified by disc diffusion testing. The occurrence of ESBL phenotypes was also assessed using the double disc synergy method. PCR/sequencing techniques were employed to examine the presence of ESBL (β-lactamase (bla)-TEM, blaSHV, and blaCTX-M), colistin (mcr-1), and carbapenem (blaNDM, blaVIM, and blaKPC) resistance genes.

Results

The findings revealed that 140 out of 250 (56%) were identified as E. coli. All E. coli isolates had a high level of multi-antimicrobial resistance (MAR) with an index value greater than 0.2, and 65.7% of them were confirmed to produce ESBL. Out of the 92 ESBL phenotypes, 55 (59.7%), 32 (34.7%), 18 (19.6%), and 37 (40.2%) isolates harbor b laTEM-3, b laSHV-4, b laCTX-M-1, a nd blaCTX-M-14 genes, respectively. The blaNDM-1 gene was identified in all 40 phenotypes that exhibited resistance to carbapenem, accounting for 28.5% of all strains of E. coli and 43.4% of ESBL isolates. The VIM and KPC genes were not detected in any of the samples. Furthermore, there was a significant prevalence of the mobilized colistin resistance (mcr)-1 gene, with 64 (69.5%) of the ESBL isolates exhibiting this gene.

Conclusion

The prevalence of ESBL-producing E. coli, particularly those resistant to carbapenem and colistin, poses a significant public health risk in society.

Distinguishing Inducible and Non-Inducible Resistance to Colistin in Pseudomonas aeruginosa by Quantitative and Systems Pharmacology Modeling at Low and Standard Inocula

Colistin is a polymyxin and peptide antibiotic that can yield rapid bacterial killing, but also leads to resistance emergence. We aimed to develop a novel experimental and Quantitative and Systems Pharmacology approach to distinguish between inducible and non-inducible resistance. Viable count profiles for the total and less susceptible populations of Pseudomonas aeruginosa ATCC 27853 from static and dynamic in vitro infection models were simultaneously modeled. We studied low and normal initial inocula to distinguish between inducible and non-inducible resistance. A novel cutoff filter approach allowed us to describe the eradication and inter-conversion of bacterial populations. At all inocula, 4.84 mg/L of colistin (sulfate) yielded ≥4 log10 killing, followed by >4 log10 regrowth. A pre-existing, less susceptible population was present at standard but not at low inocula. Formation of a non-pre-existing, less susceptible population was most pronounced at intermediate colistin (sulfate) concentrations (0.9 to 5 mg/L). Both less susceptible populations inter-converted with the susceptible population. Simultaneously modeling of the total and less susceptible populations at low and standard inocula enabled us to identify the de novo formation of an inducible, less susceptible population. Inducible resistance at intermediate colistin concentrations highlights the importance of rapidly achieving efficacious polymyxin concentrations by front-loaded dosage regimens.

Conversion to colistin susceptibility by tigecycline exposure in colistin-resistant Klebsiella pneumoniae and its implications to combination therapy

OBJECTIVES

This study investigated the effect of tigecycline exposure on susceptibility of colistin-resistant Klebsiella pneumoniae isolates to colistin and explored the possibility of antibiotic combination at low concentrations to treat colistin-resistant K. pneumoniae isolates.

METHODS

Twelve tigecycline-resistant (TIR) mutants were induced in vitro from wild-type, colistin-resistant, and tigecycline-susceptible K. pneumoniae isolates. Antibiotic susceptibility was determined using the broth microdilution method. The deduced amino acid alterations were identified for genes associated with colistin resistance, lipid A biosynthesis, and tigecycline resistance. Expression levels of genes were compared between wild-type stains and TIR mutants using quantitative real-time polymerase chain reaction (PCR). Lipid A modification was explored using MALDI-TOF mass spectrometry. Time-killing assay was performed to assess the efficiency of combination therapy using low concentrations of colistin and tigecycline.

RESULTS

All TIR mutants except one were converted to be susceptible to colistin. These TIR mutants had mutations in the ramR gene and increased expression levels of ramA. Three genes associated with lipid A biosynthesis, lpxC, lpxL, and lpxO, were also overexpressed in TIR mutants, although no mutation was observed. Additional polysaccharides found in colistin-resistant, wild-type strains were modified in TIR mutants. Colistin-resistant K. pneumoniae strains were eliminated in vitro by combining tigecycline and colistin at 2 mg/L. In this study, we found that tigecycline exposure resulted in reduced resistance of colistin-resistant K. pneumoniae to colistin. Such an effect was mediated by regulation of lipid A modification involving ramA and lpx genes.

CONCLUSION

Because of such reduced resistance, a combination of colistin and tigecycline in low concentrations could effectively eradicate colistin-resistant K. pneumoniae strains.

Clinical Efficacy and Safety of Colistin Sulfate in the Treatment of Carbapenem-Resistant Organism Infections in Patients with Hematological Diseases

INTRODUCTION

Carbapenem-resistant organisms (CRO) have emerged as a significant worldwide issue. However, the availability of efficacious antibiotics for treating CRO infections remains limited. Polymyxins, including colistin sulfate, represent the last-line therapeutic option against CRO infections. This study aims to retrospectively evaluate the clinical effectiveness and safety of colistin sulfate in managing CRO infections among patients with hematological diseases.

METHODS

Between April 2022 and January 2023, a total of 118 hematological patients diagnosed with CRO infection were treated with colistin sulfate at Suzhou Hongci Hospital of Hematology. The assessment encompassed the clinical efficacy, bacterial clearance rate, adverse reactions, and 30-day all-cause mortality.

RESULTS

The study found that the total effective rate of colistin sulfate in the treatment of CRO infection was 74.6%, with a bacterial clearance rate of 72.6%. Throughout the treatment, nephrotoxicity occurred in 7.6% of cases, neurotoxicity in 2.5% of cases, and the 30-day all-cause mortality rate was 22.9%. Multivariate logistic analysis revealed that the treatment course and combination medication with other antimicrobials were independent factors affecting the clinical efficacy of colistin sulfate.

CONCLUSION

Our study demonstrates that the treatment of colistin sulfate can achieve high clinical efficacy and microbial responses, with a low risk of nephrotoxicity. This study provides evidence of the positive clinical efficacy and safety of colistin sulfate treatment in these patients. High-quality randomized controlled trials are still needed to further confirm the beneficial role of colistin sulfate.

Prostaglandin F2α analogue, bimatoprost ameliorates colistin-induced nephrotoxicity

Colistin (polymyxin E) is an antibiotic that is effective against multidrug-resistant gram-negative bacteria. However, the high incidence of nephrotoxicity caused by colistin limits its clinical use. To identify compounds that might ameliorate colistin-induced nephrotoxicity, we obtained 1707 compounds from the Korea Chemical Bank and used a high-content screening (HCS) imaging-based assay. In this way, we found that bimatoprost (one of prostaglandin F2α analogue) ameliorated colistin-induced nephrotoxicity. To further assess the effects of bimatoprost on colistin-induced nephrotoxicity, we used in vitro and in vivo models. In cultured human proximal tubular cells (HK-2), colistin induced dose-dependent cytotoxicity. The number of terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL)-positive cells, indicative of apoptosis, was higher in colistin-treated cells, but this effect of colistin was ameliorated by cotreatment with bimatoprost. The generation of reactive oxygen species, assessed using 2,7-dichlorodihydrofluorescein diacetate, was less marked in cells treated with both colistin and bimatoprost than in those treated with colistin alone. Female C57BL/6 mice (n = 10 per group) that were intraperitoneally injected with colistin (10 mg/kg/12 hr) for 14 days showed high blood urea nitrogen and serum creatinine concentrations that were reduced by the coadministration of bimatoprost (0.5 mg/kg/12 hr). In addition, kidney injury molecule-1 (KIM1) and Neutrophil gelatinase-associated lipocalin (NGAL) expression also reduced by bimatoprost administration. Further investigation in tubuloid and kidney organoids also showed that bimatoprost attenuated the nephrotoxicity by colistin, showing dose-dependent reducing effect of KIM1 expression. In this study, we have identified bimatoprost, prostaglandin F2α analogue as a drug that ameliorates colistin-induced nephrotoxicity.

Detection and genomic characterization of a multidrug-resistant Salmonella Newport co-harbouring blaCMY-2, qnrB19 and mcr-9 from the diarrheic faeces of a foal

OBJECTIVES

This study reports the genomic characterization of the multidrug resistant Salmonella Newport strain 195_20 recovered from the diarrheic faeces of a foal in Brazil and co-harbouring the mcr-9, blaCMY-2 and qnrB19 antibiotic resistance genes.

METHODS

Bacterial isolate positive for mobile colistin resistance gene (mcr-9) was submitted to antimicrobial susceptibility testing by disk diffusion and broth microdilution for colistin and polymyxin B. The isolate was submitted to whole genome sequencing by Illumina technology and Nanopore Sequencing. Conjugation assays, plasmid sizes determined by S1-PFGE and plasmid content were investigated by hybrid assembly after MinIon long reads sequencing.

RESULTS

Isolate 195_20 was identified as sequence type ST45, resistant to penicillin and cephalosporins (ampicillin, ceftazidime, ceftriaxone and cefotaxime), aminoglycosides (streptomycin and gentamicin), phenicol (chloramphenicol), quinolones and fluoroquinolones (nalidixic acid, ciprofloxacin, and pefloxacin), folate pathway antagonists (sulfonamides and trimethoprim-sulfamethoxazole), and tetracycline. A transferable IncHI2/IncHI2A plasmid sized ca. 262kb was found to carry the mcr-9 gene in a module consisting of IS903-mcr-9-wbuC-IS26. In addition, an 174kb IncC and a 48kb IncN plasmid were also identified in the 195_20 isolate, carrying blaCMY-2 and qnrB19, respectively.

CONCLUSIONS

Not surprisingly, isolate 195_20 was susceptible to polymyxins, possibly due to absence of qseBC regulatory operon. Presence of mobile colistin resistance (mcr-9), third-generation cephalosporins (blaCMY-2) and quinolone (qnrB19) resistance determinants in zoonotic pathogens from animals in close contact with humans alerts for the possible route of transmission between these different reservoirs.