Current and future perspectives in the treatment of multidrug-resistant Gram-negative infections

Association of fluoroquinolone resistance with rare quinolone resistance-determining region (QRDR) mutations and protein-quinolone binding affinity (PQBA) in multidrug-resistant Escherichia coli isolated from patients with urinary tract infection

BACKGROUND

Urinary tract infections (UTIs) caused by Escherichia coli pose significant public health risks, particularly in developing countries like Bangladesh. This study aimed to elucidate resistance patterns among UTI isolates and comprehensively investigate the mutational spectrum and its impact on drug-microbe interactions.

METHODS

We collected and identified E. coli isolates from hospitalized UTI patients at Dhaka Medical College Hospital and determined their resistance patterns using the disc diffusion method and broth microdilution. Quinolone resistance-determining regions (QRDRs) of the target genes (gyrA, gyrB, parC, and parE) associated with fluoroquinolone resistance were amplified by polymerase chain reaction (PCR) and analyzed through BTSeq™ sequencing for mutations, followed by molecular docking analysis using PyMOL and AutoDock for the protein-quinolone binding affinity (PQBA) study.

RESULTS

All isolates (100 %) displayed multidrug resistance, with chloramphenicol (16 % resistant) and colistin (28 % resistant) demonstrating superior efficacy compared to other antibiotics. The isolates resistant to colistin, as determined by disc diffusion testing, exhibited remarkably high minimum inhibitory concentrations (MICs), with one isolate registering an MIC exceeding 512 µg/mL. Alarming resistance rates were observed for five antibiotic classes, except for polymyxins (28 % resistant) and protein synthesis inhibitors (48 % resistant). Fifty-two percent (52 %) of the isolates exhibited resistance to all five tested quinolones. Sequence analysis revealed a novel L88Q mutation in ParC, affecting PQBA and binding conformation. Additionally, three ParC mutations (S80I, E84V, and E84G) and two ParE mutations (S458A and I529L) were identified, which had not been previously reported in Bangladesh. Among these, S80I appeared in all isolates. Double-mutations (S83L+D87N) in GyrA, L88Q and S80I in ParC, and I529L in ParE were identified as key drivers of fluoroquinolone resistance.

CONCLUSION

Our findings underscore the accumulation of significant mutations within QRDRs of UTI isolates, potentially compromising fluoroquinolone efficacy. The emergence of these novel mutations warrants further investigation to impede their dissemination and combat quinolone resistance.

Antimicrobial use regulations are associated with increased susceptibility among bovine Salmonella isolates from a U.S. surveillance system

Health authorities around the world have called to limit antimicrobial use in food-producing animals. In the United States, two recent regulatory actions have changed the use of antimicrobials in livestock, banning production uses in 2017 and restricting extra-label use of cephalosporins in 2012. This study aimed to assess the impact of the 2012 and 2017 regulations on antimicrobial use in cattle in the United States by analyzing 18,627 bovine Salmonella AMR susceptibility patterns using data from the National Antimicrobial Resistance Monitoring System (NARMS). Logistic regression was used to model the odds of being a susceptible isolate. Additionally, interval-censored accelerated failure time (AFT) models were used to analyze changes in minimum inhibitory concentrations (MICs) over time and by serotype. The most common serotypes were Montevideo (n = 3003), Anatum (n = 1394), Cerro (n = 1373), and Typhimurium (n = 1213). Susceptibility was highest for azithromycin (99 %), ciprofloxacin, gentamicin, and trimethoprim-sulfamethoxazole (all 98 %), and lowest for tetracycline (76 %), chloramphenicol (86 %), and ampicillin (85 %). Serotypes Typhimurium, Newport, and Dublin exhibited lower susceptibility compared to other serotypes. Susceptibility to all antimicrobials increased during the periods 2013-2017 and 2018-2022 compared to isolates before 2012, with a greater increase in 2018-2022. MICs decreased for most antimicrobials except for chloramphenicol and gentamicin, which showed increased median MIC for the periods 2013-2017 and 2018-2022, respectively. In conclusion, antimicrobial use restrictions appear correlated with a reduction in Salmonella AMR, although this effect cannot be untangled from the effect of time in this dataset.

Navigating Antibiotic Resistance in Gram-Negative Bacteria: Current Challenges and Emerging Therapeutic Strategies

The rapid rise of antibiotic resistance poses a severe global health crisis, necessitating new approaches to counter this growing threat. The problem is exacerbated in Gram-negative bacterial pathogens as many antibiotics are unable to enter these cells owing to their unique additional outer membrane barrier. In this review, we discuss the challenges of targeting Gram-negative bacteria, including the complexity of the outer membrane, as well as the presence of efflux pumps and β-lactamases that contribute to resistance. We also review solutions proposed to facilitate the entry and accumulation of antibiotics in Gram-negative bacteria. These involve using existing antibiotics in combination with other inhibitors to attack the bacterial cell synergistically. We also highlight approaches to target Gram-negative pathogens via novel modes of action, providing new strategies to tackle antibiotic resistance.

Predictive factors for 30-day mortality after polymyxin B treatment of carbapenem-resistant Gram-negative bacilli infections

OBJECTIVES

This study aimed to investigate the associated factors predicting 30-day mortality of carbapenem-resistant Gram-negative bacilli (CR-GNB) infections, with focus on polymyxin B AUCss,24h/MIC.

METHODS

This prospective cohort study included patients with CR-GNB infections from January 2022 to January 2024. The primary outcome was 30-day mortality. Classification and regression tree (CART) analysis was used to calculate the AUCss,24h/MIC threshold for 30-day mortality. Multivariate analysis was conducted to assess risk factors affecting this outcome.

RESULTS

We enrolled 107 patients, among which 30-day mortality occurred in 31 (29.0%) cases. The CART-derived AUCss,24h/MIC breakpoint was 51.3, and patients in the below-breakpoint group had 3.4-fold higher 30-day mortality than those in the above-breakpoint group (58.1% vs 17.1%, P < 0.001). On multivariate analysis, polymyxin B AUCss,24h/MIC of ≥51.3 (aOR 0.08, P = 0.001) predicted a lower risk for 30-day mortality. In subgroup analysis, the survival benefit of AUCss,24h/MIC target attainment remained in patients with high risk of mortality or carbapenem-resistant Acinetobacter baumannii infections.

CONCLUSIONS

Polymyxin B AUCss,24h/MIC of ≥51.3 independently predicted lower 30-day mortality in treating CR-GNB infections. Further studies should verify the AUCss,24h/MIC target associated with survival outcomes in larger randomized controlled trials.

Real-World Applications of Imipenem-Cilastatin-Relebactam: Insights From a Multicenter Observational Cohort Study

Background

Multidrug-resistant (MDR) gram-negative infections are a substantial threat to patients and public health. Imipenem-cilastatin-relebactam (IMI/REL) is a β-lactam/β-lactamase inhibitor with expanded activity against MDR Pseudomonas aeruginosa and carbapenem-resistant Enterobacterales. This study aims to describe the patient characteristics, prescribing patterns, and clinical outcomes associated with IMI/REL.

Methods

This was a retrospective, multicenter, observational study of patients ≥18 years old who received IMI/REL for ≥48 hours for a suspected or confirmed gram-negative infection. The primary outcome was clinical success, defined as improvement or resolution of infection-related signs or symptoms while receiving IMI/REL and the absence of 30-day microbiologic failure. Multivariable logistic regression analysis was performed to identify independent predictors of clinical success.

Results

The study included 151 patients from 24 US medical centers. IMI/REL was predominantly prescribed for lower respiratory tract infections, accounting for 52.3% of cases. Most patients were infected with a carbapenem-nonsusceptible pathogen (85.4%); P aeruginosa was frequently targeted (72.2%). Clinical success was achieved in 70.2% of patients. Heart failure, receipt of antibiotics within the past 90 days, intensive care unit admission at time of index culture collection, and isolation of difficult-to-treat resistant P aeruginosa were independently associated with a reduced odds of clinical success. Adverse events were reported in 6.0% of patients, leading to discontinuation of IMI/REL in 3 instances.

Conclusions

This study provides a comprehensive analysis of the real-world effectiveness and safety of IMI/REL. Comparative studies and investigations of specific subgroups will further enhance our understanding of IMI/REL in treating MDR infections.

Antibiotic Resistance and Mortality in ICU Patients: A Retrospective Analysis of First Culture Growth Results

OBJECTIVES

This study aimed to analyze the antibiotic resistance patterns of microorganisms isolated from intensive care unit (ICU) patients and evaluate their impact on mortality and length of ICU stay. Given the increasing prevalence of multidrug-resistant (MDR) pathogens in critically ill patients, understanding their resistance profiles is crucial for optimizing empirical antibiotic therapy and improving patient outcomes.

METHODS

This retrospective study included 237 ICU patients admitted between 1 July 2022, and 1 January 2024. The initial culture growth results from blood and urine samples were analyzed. Microorganism identification was performed using VITEK 2 Compact and conventional bacteriological methods, while antibiotic susceptibility testing followed CLSI 2022 and EUCAST 2022 guidelines.

RESULTS

A total of 237 ICU patients were included in this study. The most frequently isolated microorganisms were Escherichia coli (E. coli) (44.3%), Klebsiella pneumoniae (K. pneumoniae) (35.0%), and Pseudomonas aeruginosa (P. aeruginosa) (25.3%), with Acinetobacter baumannii (A. baumannii) (31.2%) being the most resistant pathogen. Among Gram-positive bacteria, methicillin-resistant Staphylococcus aureus (MRSA) (12.2%) and vancomycin-resistant enterococci (VRE) (21.5%) were the most frequently identified multidrug-resistant (MDR) pathogens. Regarding antimicrobial resistance, carbapenem resistance was highest in A. baumannii (55%), followed by P. aeruginosa (40%) and K. pneumoniae (30%). Additionally, ESBL-producing E. coli (43.2%) and K. pneumoniae (38.5%), as well as carbapenemase-producing K. pneumoniae (18.6%) and E. coli (9.2%), were identified as key resistance mechanisms impacting clinical outcomes. Patients with MDR infections had significantly longer ICU stays (p < 0.05) and higher mortality rates. The Kaplan-Meier survival analysis revealed that A. baumannii infections were associated with the highest mortality risk (HR: 4.6, p < 0.001), followed by MRSA (HR: 3.5, p = 0.005) and P. aeruginosa (HR: 2.8, p = 0.01). Among laboratory biomarkers, elevated procalcitonin (≥2 ng/mL, OR: 2.8, p = 0.008) and CRP (≥100 mg/L, OR: 2.2, p = 0.01) were significantly associated with ICU mortality. Additionally, patients who remained in the ICU for more than seven days had a 1.4-fold increased risk of mortality (p = 0.02), further emphasizing the impact of prolonged hospitalization on adverse outcomes.

CONCLUSIONS

MDR pathogens, particularly A. baumannii, MRSA, P. aeruginosa, and K. pneumoniae, are associated with longer ICU stays and higher mortality rates. Carbapenem, cephalosporin, fluoroquinolone, and aminoglycoside resistance significantly impact clinical outcomes, emphasizing the urgent need for antimicrobial stewardship programs. ESBL, p-AmpC, and carbapenemase-producing Enterobacterales further worsen patient outcomes, highlighting the need for early infection control strategies and optimized empirical antibiotic selection. Biomarkers such as procalcitonin and CRP, alongside clinical severity scores, serve as valuable prognostic tools for ICU mortality.

Impact of high frequency electromagnetic radiation on bacterial survival and antibiotic activity in exposed bacteria

High-frequency electromagnetic waves (HFEMWs) have been shown to influence cellular functions, including bacterial behavior, potentially affecting growth and antibiotic sensitivity. This study evaluated the response of Escherichia coli and Staphylococcus aureus to HFEMWs across a frequency range of 900 MHz to 73 GHz. The Bacterial sensitivity to antibiotics, including ceftazidime, ceftaroline, gentamycin, doxycycline, and ciprofloxacin, was assessed. The growth rate was evaluated by measuring the optical density (OD) and the number of colony-forming units (CFUs). Our results revealed significant electromagnetic interference (EMI) effects at frequencies of 51.8 GHz and 53 GHz, with 53 GHz showing the most pronounced impact. These frequencies enhanced bacterial susceptibility, with previously resistant E. coli and S. aureus strains becoming sensitive to tested antibiotics. Conversely, 70.6 GHz and 73 GHz frequencies showed limited effects, while exposure to 900 MHz and 1800 MHz caused no notable changes. These findings highlight the frequency-dependent effects of HFEMWs on bacterial viability and antibiotic sensitivity. This research underscores the potential of HFEMWs as a complementary antimicrobial strategy, offering opportunities for improved infection control and innovative sterilization technologies to mitigate hospital-acquired infections.

Role of Divalent Ions in Membrane Models of Polymyxin-Sensitive and Resistant Gram-Negative Bacteria

Polymyxins, critical last-resort antibiotics, impact the distribution of membrane-bound divalent cations in the outer membrane of Gram-negative bacteria. We employed atomistic molecular dynamics simulations to model the effect of displacing these ions. Two polymyxin-sensitive and two polymyxin-resistant models of the outer membrane of Salmonella enterica were investigated. First, we found that the removal of all calcium ions induces global stress on the model membranes, leading to substantial membrane restructuring. Next, we used enhanced sampling methods to explore the effects of localized stress by displacing membrane-bound ions. Our findings indicate that creating defects in the membrane-bound ion network facilitates polymyxin permeation. Additionally, our study of polymyxin-resistant mutations revealed that divalent ions in resistant model membranes are less likely to be displaced, potentially contributing to the increased resistance associated with these mutations. Lastly, we compared results from all-atom molecular dynamics simulations with coarse-grained simulations, demonstrating that the choice of force field significantly influences the behavior of membrane-bound ions under stress.

Epidemiological and genomic analysis revealed the significant role of flies in dissemination of carbapenem-resistant Enterobacteriaceae (CRE) in China

While the role of flies as potential vectors for bacterial transmission is well recognized, the epidemiological features and genomic characteristics of associated antimicrobial-resistant strains remain underexplored. This study conducted a nationwide surveillance including 3689 flies and 838 isolates from sixteen human communities (HCs) and eight animal farms (AFs) across 21 provinces in China. Our findings revealed high carriage rates of carbapenem-resistant Enterobacteriaceae (CRE) in flies, with 27.0 % in AFs and 15.3 % in HCs. Among the 705 CRE strains identified, Providencia spp. (n = 356) and Escherichia coli (n = 231) were predominant, with 90.6 % attributed to the dissemination of the blaNDM gene. Phylogenetic tree analysis highlighted frequent clonal transmission events, with over 18 and 13 clonal evolutionary clades in Providencia spp. and E. coli, respectively. Notably, spearman analysis linked the increase of CRE prevalence in AFs flies to environmental factors like precipitation (p < 0.028) and temperature (p < 0.037), while in HCs, it positively corelated with the total meat production (p < 0.027) in each province except for Hainan. Despite significant differences in ciprofloxacin resistance (p ≤ 0.001) among E. coli strains from HCs and AFs, core genome cluster analysis and Uniform Manifold Approximation and Projection (UMAP) approach indicated these strains exhibiting close relatedness to clinical strains. This comprehensive study underscores the critical role of flies in the escalation of CRE spread within the ecosystem in China. Flies found in both HCs and AFs contribute to the dissemination of CRE, highlighting the need for urgent interventions to address this pressing issue.

The evolution of knowledge for treating Gram-negative bacterial infections

PURPOSE OF REVIEW

Infections caused by nonprimarily pathogenic Gram-negative bacilli (GNB) have been increasingly reported from the second half of the 20th century to the present. This phenomenon has expanded during the antibiotic era and in the presence of immunodeficiency.Before the discovery of sulphonamides and penicillin G, infections caused by GNB were rare compared to Gram-positive infections. The advent of anticancer therapy, the expansion of surgical procedures, the use of corticosteroids, and the implantation of prosthetic materials, along with better control of Gram-positive infections, have promoted the current increase in GNB infections.GNB have similar antimicrobial targets to Gram-positive bacteria. However, only antibiotics that can penetrate the double membrane of GNB and remain in them for a sufficient duration have antibacterial activity against them.

RECENT FINDINGS

Sulphonamides and early penicillins had limited activity against GNB. Ampicillin and subsequent beta-lactams expanded their spectrum to treat GNB. Aminoglycosides may re-surge with less toxic drugs, as highly resistant to beta-lactams GNB rise. Polymyxins, tetracyclines, and fluoroquinolones are also used for GNB. Combinations with other agents may be needed in specific cases, such as in the central nervous system and prostate, where beta-lactams may have difficulty reaching the infection site.Alternatives to current treatments must be sought in the discovery of new drug families and therapies such as phage therapy combined with antibiotics.

SUMMARY

Narrower-spectrum immunosuppressive therapies and antibiotics, antimicrobials that minimally intervene with the human microbiota, and instant diagnostic methods are necessary to imagine a future where currently dominant bacteria in infectious pathology lose their preeminence.

Prophylaxis Options in Children With a History of Recurrent Urinary Tract Infections: A Systematic Review

CONTEXT

The prevention of urinary tract infection recurrence (UTI) in children has been a challenge yet to be solved. Current practice in children with recurrent UTI (RUTI) suggests that antibiotic prophylaxis may prevent further episodes of UTI and future complications.

OBJECTIVE

To conduct a systematic review and meta-analysis of randomized controlled trials comparing prophylaxis options for the prevention of UTI and kidney scarring in children with a history of RUTI.

DATA SOURCES

We conducted a systematic literature search through major electronic databases (PubMed/Medline, Scopus and Cochrane Library) up to November 26th, 2023. Mean difference and SD were used for continuous outcomes and odds ratio for dichotomous outcomes.

STUDY SELECTION

Our meta-analysis included 3335 participants from 23 studies.

DATA EXTRACTION

The primary outcome was the effect of the different prophylaxis options on the incidence of symptomatic UTI in children with RUTI during prophylactic treatment.

RESULTS

Cranberry products and nitrofurantoin lead to lower odds of symptomatic UTI episodes during prophylaxis compared with the control group and control, trimethoprim-sulfamethoxazole, or trimethoprim groups accordingly. Nitrofurantoin may be the best option for UTI incidence reduction compared with all available documented interventions.

LIMITATIONS

No prophylaxis option has been shown to reduce kidney scarring.

CONCLUSIONS

Nitrofurantoin and cranberry products may decrease the incidence of symptomatic UTI episodes in pediatric patients with a history of RUTI. Future randomized control trials studying nonantibiotic prophylaxis options focusing on children with UTI recurrence and the risk for kidney scarring are needed to draw further conclusions.

Paeonol potentiates colistin efficacy against K. pneumoniae by promoting membrane disruption and oxidative damage

BACKGROUND

Although colistin is widely recognized as the last line of antibiotics against gram-negative bacteria, the emergence and spread of colistin resistance severely diminish its clinical efficacy and application. An alternative strategy to alleviate this crisis is to identify promising colistin adjuvants with enhanced antibacterial activity.

PURPOSE

In this study, the adjuvant effects of paeonol on colistin and the underlying mechanisms were investigated.

METHOD

Minimum Inhibitory Concentration (MIC) and checkerboard assays were used to investigate the adjuvant activity and structure-activity relationship of paeonol on the antibacterial effect of colistin in vitro. Time-dependent killing and resistance development assays were used to investigate the bactericidal effects and emergence of colistin resistance. Different fluorescent probes and competitive inhibition tests were used to investigate bacterial membrane functions and potential targets. Skin infection and peritonitis-sepsis models were used to evaluate the combined in vivo effects of colistin and paeonol in vivo.

RESULT

Paeonol enhanced the antibacterial effects of colistin against gram-negative bacteria, particularly Klebsiella pneumoniae. Structure-activity relationship analysis showed that the hydroxyl, 4-methoxy and ketone carbonyl side chains of the benzene ring contributed to the adjuvant effect of paeonol. Paeonol enhances the bactericidal effects of colistin and minimizes the emergence of colistin resistance. Notably, mechanistic studies demonstrated that the combination of colistin and paeonol enhances membrane disruption and oxidative damage, possibly via interactions with phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and cardiolipin (CAL). Importantly, paeonol enhanced the efficacy of colistin in both the skin and peritonitis infection models.

CONCLUSION

This is the first report on the adjuvant potential of paeonol in colistin to combat K. pneumoniae by promoting membrane disruption and oxidative damage via targeting membrane phospholipids. Notably, the verified target, PE, provides an additional avenue for screening new colistin adjuvants.The combination therapy of paeonol and colistin is a promising strategy for treating infections caused by gram-negative pathogens to address antibiotic resistance issues.

The Use of Cefiderocol in Gram-Negative Bacterial Infections at International Medical Center, Jeddah, Saudi Arabia

BACKGROUND/OBJECTIVES

The necessity for ground-breaking treatments for Gram-negative infections is evident. The World Health Organization, the Infectious Diseases Society of America, and the European Commission have highlighted the critical insufficiency of efficient antibiotics, urging pharmaceutical businesses to manufacture new antibiotics. Therefore, developing new antibiotics with broad efficacy against Gram-negative pathogens is essential. Thus, this research aimed to evaluate the safety and effectiveness of cefiderocol in treating multidrug-resistant Gram-negative bacterial infections at the International Medical Center (IMC), Jeddah, Saudi Arabia.

METHODS

A retrospective analysis was conducted on patients treated from January 2021 to February 2023. Thirteen case groups treated with cefiderocol were compared to twenty control groups treated with other antibiotics.

RESULTS

The results indicated no statistically significant differences in ICU stay, comorbidity indices, or mortality rates between the two groups. Cefiderocol showed high clinical and microbiological cure rates, despite the severity of the patients' conditions. Carbapenem-resistant Klebsiella pneumoniae and difficult-to-treat resistance Pseudomonas aeruginosa were the most prevalent pathogens in the case and control group, respectively. Two patients treated with cefiderocol developed Clostridioides difficile infection, emphasizing the need for close monitoring of potential adverse effects.

CONCLUSIONS

The results of this study support cefiderocol as a viable alternative for managing serious infections instigated by multidrug-resistant Gram-negative bacteria.

Epidemiology, antimicrobial resistance profile and management of carbapenem-resistant Klebsiella pneumoniae among mothers with suspected sepsis in Ethiopia

BACKGROUND

Early detection and proper management of maternal sepsis caused by carbapenem-resistant Klebsiella pneumoniae (CRKP) can significantly reduce severe complications and maternal mortality. This study aimed to describe the epidemiology, antimicrobial resistance profile, and management of carbapenem-resistant K. pneumoniae among sepsis-suspected maternal cases in Ethiopia.

METHODS

A prospective cross-sectional study was conducted in five tertiary hospitals from June 2021 to December 2023. Isolation, identification, and antimicrobial susceptibility testing of the isolates were carried out following standard microbiological procedures as stated in the CLSI guidelines. Data on socio-demographics, risk factors, and management strategies were collected with structured questionnaires. Associations between variables were determined using logistic regression analysis in STATA-21. A p-value of less than 0.05 was statistically significant.

RESULTS

Of the 5613 total women suspected of having maternal sepsis, 609 (10.8%) of them were infected with K. pneumoniae. The prevalence rates of MDR, XDR, and PDR K. pneumoniae strains were 93.9%, 24.3%, and 10.9%, respectively. The resistance rates for the last-resort antibiotics; amikacin, tigecycline, carbapenem, and third-generation cephalosporin were 16.4%, 29.1%, 31.9%, and 93.0%, respectively. The combination of carbapenem with tigecycline or amikacin therapy was used to manage maternal sepsis caused by cephalosporin-and carbapenem-resistant strains. Sepsis associated risk factors, including septic abortion [AOR = 5.3; 95%CI:2.2-14.4]; extended hospitalization [AOR = 3.7; 95%CI: 1.6-19.4]; dilatation and curettage [AOR = 2.2; 95%CI:1.3-13.4]; cesarean wound infection [AOR = 4.1; 95%CI:2.0-9.2]; indwelling catheterization [AOR = 2.1;95%CI: 1.4-6.2]; ICU admission [AOR = 4.3; 95%CI:2.4-11.2]; post abortion [AOR = 9.8; 95%CI:5.7-16.3], and recurrent UTI [AOR = 3.3; 95%CI: 1.6-13.2] were significantly associated with maternal sepsis caused by K. pneumoniae.

CONCLUSIONS

The prevalence of maternal sepsis caused by carbapenem- resistant K. pneumoniae is high and serious attention needs to be given to combat transmission. Therefore, improving awareness, early diagnosis, IPC, integrated maternal surveillance, improved sanitation and efficient antimicrobial stewardship are crucial to combating bacterial maternal sepsis.

Antimicrobial Resistance in Sepsis Cases Due to Escherichia coli and Klebsiella pneumoniae: Pre-Pandemic Insights from a Single Center in Southwestern Romania

Sepsis is an uncontrolled reaction of the body to an infection, and if not effectively treated, it can progress to septic shock, multiple organ failure, and ultimately, death.

OBJECTIVE

To determine the resistance profile of Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae) strains isolated in sepsis cases diagnosed at the Infectious Diseases Clinic in Craiova, Romania.

METHODS

The bacteria responsible for sepsis cases were identified using the Vitek 2 Systems version 06.01, which was then employed to assess their antimicrobial susceptibility (Global CLSI and Phenotypic 2017).

RESULTS

We have identified 989 patients diagnosed with bacterial sepsis. Among these, 953 cases were caused by Gram-negative rods, with 415 attributed to E. coli and 278 to K. pneumoniae. High levels of resistance to ampicillin were recorded for E. coli strains isolated in sepsis cases (64.6%); adding sulbactam lowers the level of resistance to 41.8%. Resistance to 3rd generation cephalosporins varied between 7.47 and 14.6% and another 3.41 to 11.1% are dose-dependent susceptibility strains. Resistance to carbapenems (i.e., ertapenem, meropenem) is low-2.18-2.42%. More than 95% of the tested K. pneumoniae strains were resistant to ampicillin and adding sulbactam as a β-lactamase inhibitor only halves that level. Resistance to 3rd generation cephalosporins varied between 20.7% and 22.5%; resistance levels for K. pneumoniae were notably higher than those for E. coli. Over 95% of K. pneumoniae strains showed resistance to ampicillin, and resistance to 3rd generation cephalosporins varied between 20.7% and 22.5%. Additionally, K. pneumoniae exhibited higher resistance to carbapenems (13.7-19.5%) compared to E. coli (2.18-2.42%).

CONCLUSIONS

Antimicrobial resistance levels are generally lower than continental and national data, except for ampicillin and carbapenems (meropenem and ertapenem). K. pneumoniae strains are significantly more resistant than E. coli strains.

Extensively Antibiotic-Resistant Bacterial Infections in Trauma Cases Managed at the Médecins Sans Frontières Tertiary Orthopaedic Center in Mosul, Iraq: A Case Series

The Médecins Sans Frontières Tertiary Orthopaedic Care center in Mosul, Iraq, provides reconstructive surgery, microbiological analysis, integrated infection prevention and control, and antibiotic stewardship services. Between May 2018 and February 2020, we recorded soft tissue and/or bone infections caused by gram-negative extensively drug-resistant (XDR) bacteria in 4.9% (13/266) of the admitted patients. The XDR bacteria identified among 12 patients in this case series were extended-spectrum β-lactamase-producing Klebsiella pneumoniae (n = 5, 41.7%) with intermediate sensitivity or resistance to imipenem and/or meropenem, Acinetobacter spp (n = 3, 25.0%; 2 Acinetobacter baumannii strains) resistant to imipenem and/or meropenem, Pseudomonas aeruginosa (n = 2, 16.7%) resistant to imipenem and meropenem, and extended-spectrum β-lactamase-producing Proteus mirabilis (n = 2, 16.7%) resistant to meropenem. Most XDR isolates were sensitive only to colistin or polymyxin B, neither of which is available in Iraq. Therefore, the only treatment option was multiple rounds of surgical debridement and wound care. The infection was deemed cured before discharge in 7 patients (58.3%). Meanwhile, 4 patients (33.3%) were discharged with unhealed wounds, and outpatient follow-up was planned. One patient died in the intensive care unit of a referral hospital after developing septicemia postsurgery. XDR bacteria pose substantial health risks in Iraq. Thus, improving antimicrobial stewardship and accessibility to essential antibiotics is critical to address this issue.

Investigating the Antimicrobial Potential of 560 Compounds from the Pandemic Response Box and COVID Box against Resistant Gram-Negative Bacteria

Antimicrobial resistance (AMR) has emerged as a significant threat to public health, particularly in infections caused by critically important Gram-negative bacteria. The development of novel antibiotics has its limitations, and therefore it is crucial to explore alternative strategies to effectively combat infections with resistant pathogens. In this context, the present study investigated the antibacterial potency of 560 compounds against the multidrug-resistant (MDR) strains of Klebsiella pneumoniae and Serratia marcescens. The evaluated compounds were selected from the Pandemic Response Box (PRB) and COVID Box (CB) and subjected to assays to determine the inhibitory concentration (IC), minimum bactericidal concentration (MBC), and biofilm formation. Further, the effects of these compounds on membrane integrity were assessed through protein quantification. Several of the evaluated compounds, including fusidic acid, MMV1580853, and MMV1634399, exhibited a significant reduction in biofilm formation and growth in K. pneumoniae. Trimethoprim exhibited potential against S. marcescens. The IC values of the compounds indicated significant microbial growth inhibition at various concentrations. These findings underscore the potency of the existing antibiotics and novel compounds in combating the MDR strains of bacteria. The importance of reconsidering the known antibiotics and utilizing drug repositioning strategies to address the increasing risk of AMR is highlighted.

Extensively and multidrug-resistant bacterial strains: case studies of antibiotics resistance

The development of antibiotic resistance compromises the effectiveness of our most effective defenses against bacterial infections, presenting a threat to global health. To date, a large number of research articles exist in the literature describing the case reports associated with extensively drug-resistant (XDR) and multidrug-resistant (MDR) bacterial strains. However, these findings are scattered, making it time-consuming for researchers to locate promising results and there remains a need for a comparative study to compile these case reports from various geographical regions including the Kingdom of Saudi Arabia. Additionally, no study has yet been published that compares the genetic variations and case reports of MDR and XDR strains identified from Saudi Arabia, the Middle East, Central Europe, and Asian countries. This study attempts to provide a comparative analysis of several MDR and XDR case reports from Saudi Arabia alongside other countries. Furthermore, the purpose of this work is to demonstrate the genetic variations in the genes underlying the resistance mechanisms seen in MDR and XDR bacterial strains that have been reported in Saudi Arabia and other countries. To cover the gap, this comprehensive review explores the complex trends in antibiotic resistance and the growing risk posed by superbugs. We provide context on the concerning spread of drug-resistant bacteria by analyzing the fundamental mechanisms of antibiotic resistance and looking into individual case reports. In this article, we compiled various cases and stories associated with XDR and MDR strains from Saudi Arabia and various other countries including China, Egypt, India, Poland, Pakistan, and Taiwan. This review will serve as basis for highlighting the growing threat of MDR, XDR bacterial strains in Saudi Arabia, and poses the urgent need for national action plans, stewardship programs, preventive measures, and novel antibiotics research in the Kingdom.

Risk factors for multidrug-resistant and extensively drug-resistant Acinetobacter baumannii infection of patients admitted in intensive care unit: a systematic review and meta-analysis

BACKGROUND

Multidrug-resistant (MDR) and extensively drug-resistant (XDR) Acinetobacter baumannii infections pose challenges for clinical treatment and cause high mortality, particularly in intensive care units (ICUs).

AIM

To systematically summarize and analyse the risk factors for MDR/XDR A. baumannii-infected patients admitted to ICUs.

METHODS

PubMed, Embase, Web of Science, and the Cochrane Library were searched for eligible original studies published in English before October 2023. Meta-analysis was conducted where appropriate, with mean differences (MDs) and odds ratios (ORs) calculated for continuous and nominal scaled data. The quality of included studies was assessed using the Newcastle-Ottawa Scale (NOS).

FINDINGS

Ten studies reporting 1199 ICU patients (604 from general ICUs, 435 from neonatal ICUs, and 160 from paediatric ICUs) from eight countries were included in our analysis. Risk factors associated with MDR A. baumannii infection among patients admitted to general ICUs included high Acute Physiology And Clinical Health II (APACHE Ⅱ) score (mean difference (MD): 7.52; 95% confidence interval (CI): 3.24-11.80; P = 0.0006), invasive procedures (odds ratio (OR): 3.47; 95% CI: 1.70-7.10; P = 0.0006), longer ICU stay (MD: 3.40; 95% CI: 2.94-3.86; P < 0.00001), and use of antibiotics (OR: 2.69; 95% CI: 1.22-5.94; P = 0.01). In the sub-group analysis, longer neonatal ICU stay (MD: 16.88; 95% CI: 9.79-23.97; P < 0.00001) was associated with XDR A. baumannii infection.

CONCLUSION

Close attention should be paid to patients with longer ICU stays, undergoing invasive procedures, using antibiotics, and with high APACHE Ⅱ scores to reduce the risk of MDR and XDR A. baumannii infections.

Antibacterial effectiveness of trans-cinnamaldehyde against foodborne Enterobacteriaceae and its adjuvant effect with gentamicin

The Enterobacteriaceae family is recognized as a primary group of Gram-negative pathogens responsible for foodborne illnesses and is frequently associated with antibiotic resistance. The present study explores the natural-based compound trans-cinnamaldehyde (TC) against drug-resistant Enterobacteriaceae and its synergism with gentamicin (GEN) to address this issue. The research employs three strains of Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae, previously isolated from shrimp. The antibacterial activity was evaluated by the disk diffusion method, microdilution test, kinetics of growth, and time-kill curve. In addition, the synergistic effect between TC/GEN was investigated by checkerboard assay. All strains showed sensitivity to TC with an inhibition zone diameter > 35 mm. The TC showed inhibitory and bactericidal action in the most tested bacteria around 625 μg/mL. Sub-inhibitory amounts (1/2 and 1/4 MIC) of TC interfered with the growth kinetics by lag phase extension and decreased the log phase. Time-kill curves show a reduction of viable cells after the first hour of TC treatment at bactericidal concentrations. The synergistic effect between TC/GEN was observed for E. coli and E. cloacae strains with FICi ranging from 0.15 to 0.50. These findings, therefore, suggest TC as a promising alternative in the fight against drug-resistant Enterobacteriaceae that can cause foodborne illnesses.

Imipenem/Cilastatin/Relebactam for Complicated Infections: A Real-World Evidence

(1) Background: Infections caused by multidrug-resistant (MDR) bacteria represent one of the major global public health problems of the 21st century. Beta-lactam antibacterial agents are commonly used to treat infections due to Gram-negative pathogens. New β-lactam/β-lactamase inhibitor combinations are urgently needed. Combining relebactam (REL) with imipenem (IMI) and cilastatin (CS) can restore its activity against many imipenem-nonsusceptible Gram-negative pathogens. (2) Methods: we performed a systematic review of the studies reporting on the use of in vivo REAL/IPM/CS. (3) Results: A total of eight studies were included in this review. The primary diagnosis was as follows: complicated urinary tract infection (n = 234), complicated intra-abdominal infections (n = 220), hospital-acquired pneumonia (n = 276), and ventilator-associated pneumonia (n = 157). Patients with normal renal function received REL/IPM/CS (250 mg/500 mg/500 mg). The most frequently reported AEs occurring in patients treated with imipenem/cilastatin plus REL/IPM/CS were nausea (11.5%), diarrhea (9.8%), vomiting (9.8%), and infusion site disorders (4.0%). Treatment outcomes in these high-risk patients receiving REL/IPM/CS were generally favorable. A total of 70.6% of patients treated with REL/IPM/CS reported a favorable clinical response at follow-up. (4) Conclusions: this review indicates that REL/IPM/CS is active against important MDR Gram-negative organisms.

Molecular Characterization of Gram-Negative Bacteria: Antimicrobial Resistance, Virulence and Epidemiology

Multidrug-resistant (MDR), extensively drug-resistant (XDR) and pan-drug-resistant (PDR) Gram-negative bacteria constitute a huge public health problem [...].

Antimicrobial resistance of Pseudomonas aeruginosa: navigating clinical impacts, current resistance trends, and innovations in breaking therapies

Pseudomonas aeruginosa, a Gram-negative bacterium, is recognized for its adaptability and opportunistic nature. It poses a substantial challenge in clinical settings due to its complicated antibiotic resistance mechanisms, biofilm formation, and capacity for persistent infections in both animal and human hosts. Recent studies revealed a potential zoonotic transmission of P. aeruginosa between animals, the environment, and human populations which highlights awareness of this microbe. Implementation of the One Health approach, which underscores the connection between human, animal, and environmental health, we aim to offer a comprehensive perspective on the current landscape of P. aeruginosa management. This review presents innovative strategies designed to counteract P. aeruginosa infections. Traditional antibiotics, while effective in many cases, are increasingly compromised by the development of multidrug-resistant strains. Non-antibiotic avenues, such as quorum sensing inhibition, phage therapy, and nanoparticle-based treatments, are emerging as promising alternatives. However, their clinical application encounters obstacles like cost, side effects, and safety concerns. Effectively addressing P. aeruginosa infections necessitates persistent research efforts, advancements in clinical development, and a comprehension of host-pathogen interactions to deal with this resilient pathogen.

Zein nanoparticles containing ceftazidime and tobramycin: antibacterial activity against Gram-negative bacteria

Aims: This work describes the encapsulation of ceftazidime and tobramycin in zein nanoparticles (ZNPs) and the characterization of their antibacterial and antibiofilm activities against Gram-negative bacteria. Materials & methods: ZNPs were synthesized by nanoprecipitation. Cytotoxicity was assessed by MTT assay and antibacterial and antibiofilm assays were performed by broth microdilution and violet crystal techniques. Results: ZNPs containing ceftazidime (CAZ-ZNPs) and tobramycin (TOB-ZNPs) showed drug encapsulation and thermal stability. Encapsulation of the drugs reduced their cytotoxicity 9-25-fold. Antibacterial activity, inhibition and eradication of biofilm by CAZ-ZNPs and TOB-ZNPs were observed. There was potentiation when CAZ-ZNPs and TOB-ZNPs were combined. Conclusion: CAZ-ZNPs and TOB-ZNPs present ideal physical characteristics for in vivo studies of antibacterial and antibiofilm activities.

Complementary supramolecular drug associates in perfecting the multidrug therapy against multidrug resistant bacteria

The inappropriate and inconsistent use of antibiotics in combating multidrug-resistant bacteria exacerbates their drug resistance through a few distinct pathways. Firstly, these bacteria can accumulate multiple genes, each conferring resistance to a specific drug, within a single cell. This accumulation usually takes place on resistance plasmids (R). Secondly, multidrug resistance can arise from the heightened expression of genes encoding multidrug efflux pumps, which expel a broad spectrum of drugs from the bacterial cells. Additionally, bacteria can also eliminate or destroy antibiotic molecules by modifying enzymes or cell walls and removing porins. A significant limitation of traditional multidrug therapy lies in its inability to guarantee the simultaneous delivery of various drug molecules to a specific bacterial cell, thereby fostering incremental drug resistance in either of these paths. Consequently, this approach prolongs the treatment duration. Rather than using a biologically unimportant coformer in forming cocrystals, another drug molecule can be selected either for protecting another drug molecule or, can be selected for its complementary activities to kill a bacteria cell synergistically. The development of a multidrug cocrystal not only improves tabletability and plasticity but also enables the simultaneous delivery of multiple drugs to a specific bacterial cell, philosophically perfecting multidrug therapy. By adhering to the fundamental tenets of multidrug therapy, the synergistic effects of these drug molecules can effectively eradicate bacteria, even before they have the chance to develop resistance. This approach has the potential to shorten treatment periods, reduce costs, and mitigate drug resistance. Herein, four hypotheses are presented to create complementary drug cocrystals capable of simultaneously reaching bacterial cells, effectively destroying them before multidrug resistance can develop. The ongoing surge in the development of novel drugs provides another opportunity in the fight against bacteria that are constantly gaining resistance to existing treatments. This endeavour holds the potential to combat a wide array of multidrug-resistant bacteria.

Antibiotics in anesthesia and critical care

Sepsis is life-threatening organ dysfunction due to a dysregulated host response to an underlying acute infection. Sepsis is a major worldwide healthcare problem. An annual estimated 48.9 million incident cases of sepsis is reported, with 11 million (20%) sepsis-related deaths. Administration of appropriate antimicrobials is one of the most effective therapeutic interventions to reduce mortality. The severity of illness informs the urgency of antimicrobial administration. Nevertheless, even used properly, they cause adverse effects and contribute to the development of antibiotic resistance. Both inadequate and unnecessarily broad empiric antibiotics are associated with higher mortality and also select for antibiotic-resistant germs. In this narrative review, we will first discuss important factors and potential confounders which may influence the occurrence of surgical site infection (SSI) and which should be considered in the provision of perioperative antibiotic prophylaxis (PAP). Then, we will summarize recent advances and perspectives to optimize antibiotic therapy in the intensive care unit (ICU). Finally, the major role of the microbiota and the impact of antimicrobials on it will be discussed. While expert recommendations help guide daily practice in the operating theatre and ICU, a thorough knowledge of pharmacokinetic/pharmacodynamic (PK/PD) rules is critical to optimize the management of complex patients and minimize the emergence of multidrug-resistant organisms.

Ag0-Ginger Nanocomposites Integrated into Natural Hydrogelated Matrices Used as Antimicrobial Delivery Systems Deposited on Cellulose Fabrics

In the textile, medical, and food industries, many of the applications have targeted the use of textile fabrics with antimicrobial properties. Obtaining eco-friendly coatings is of wide interest, especially for applications related to wound dressing or to food packaging. In order to obtain coatings with antimicrobial properties through environmentally friendly methods, a series of experiments were carried out on the use of natural polymers loaded with silver nanoparticles. In this study, coatings with antimicrobial properties were obtained by depositing natural composites based on rice flour, carob flour, or alginate on cotton fabrics. These antimicrobial coatings were multicomponent systems, in which the host matrix was generated via hydration of natural polymers. The nanocomposite obtained from the phytosynthesis of silver particles in ginger extract was embedded in hydrogel matrices. The multicomponent gels obtained by embedding silver nanoparticles in natural polymer matrices were deposited on cotton fabric and were studied in relation to nanoparticles and the type of host matrix, and the antimicrobial activity was evaluated. Fabrics coated with such systems provide a hydrophilic surface with antimicrobial properties and can therefore be used in various areas where textiles provide antibacterial protection.

Sepsis Stewardship: The Puzzle of Antibiotic Therapy in the Context of Individualization of Decision Making

The main recent change observed in the field of critical patient infection has been universal awareness of the need to make better use of antimicrobials, especially for the most serious cases, beyond the application of simple and effective formulas or rigid protocols. The increase in resistant microorganisms, the quantitative increase in major surgeries and interventional procedures in the highest risk patients, and the appearance of a significant number of new antibiotics in recent years (some very specifically directed against certain mechanisms of resistance and others with a broader spectrum of applications) have led us to shift our questions from "what to deal with" to "how to treat". There has been controversy about how best to approach antibiotic treatment of complex cases of sepsis. The individualized and adjusted dosage, the moment of its administration, the objective, and the selection of the regimen are pointed out as factors of special relevance in a critically ill patient where the frequency of resistant microorganisms, especially among the Enterobacterales group, and the emergence of multiple and diverse antibiotic treatment alternatives have made the appropriate choice of antibiotic treatment more complex, requiring a constant updating of knowledge and the creation of multidisciplinary teams to confront new infections that are difficult to treat. In this article, we have reviewed the phenomenon of the emergence of resistance to antibacterials and we have tried to share some of the ideas, such as stewardship, sparing carbapenems, and organizational, microbiological, pharmacological, and knowledge tools, that we have considered most useful and effective for individualized decision making that takes into account the current context of multidrug resistance. The greatest challenge, therefore, of decision making in this context lies in determining an effective, optimal, and balanced empirical antibiotic treatment.

Drug Discovery in the Field of β-Lactams: An Academic Perspective

β-Lactams are the most widely prescribed class of antibiotics that inhibit penicillin-binding proteins (PBPs), particularly transpeptidases that function in peptidoglycan synthesis. A major mechanism of antibiotic resistance is the production of β-lactamase enzymes, which are capable of hydrolyzing β-lactam antibiotics. There have been many efforts to counter increasing bacterial resistance against β-lactams. These studies have mainly focused on three areas: discovering novel inhibitors against β-lactamases, developing new β-lactams less susceptible to existing resistance mechanisms, and identifying non-β-lactam inhibitors against cell wall transpeptidases. Drug discovery in the β-lactam field has afforded a range of research opportunities for academia. In this review, we summarize the recent new findings on both β-lactamases and cell wall transpeptidases because these two groups of enzymes are evolutionarily and functionally connected. Many efforts to develop new β-lactams have aimed to inhibit both transpeptidases and β-lactamases, while several promising novel β-lactamase inhibitors have shown the potential to be further developed into transpeptidase inhibitors. In addition, the drug discovery progress against each group of enzymes is presented in three aspects: understanding the targets, screening methodology, and new inhibitor chemotypes. This is to offer insights into not only the advancement in this field but also the challenges, opportunities, and resources for future research. In particular, cyclic boronate compounds are now capable of inhibiting all classes of β-lactamases, while the diazabicyclooctane (DBO) series of small molecules has led to not only new β-lactamase inhibitors but potentially a new class of antibiotics by directly targeting PBPs. With the cautiously optimistic successes of a number of new β-lactamase inhibitor chemotypes and many questions remaining to be answered about the structure and function of cell wall transpeptidases, non-β-lactam transpeptidase inhibitors may usher in the next exciting phase of drug discovery in this field.

PhageGE: an interactive web platform for exploratory analysis and visualization of bacteriophage genomes

BACKGROUND

Antimicrobial resistance is a serious threat to global health. Due to the stagnant antibiotic discovery pipeline, bacteriophages (phages) have been proposed as an alternative therapy for the treatment of infections caused by multidrug-resistant pathogens. Genomic features play an important role in phage pharmacology. However, our knowledge of phage genomics is sparse, and the use of existing bioinformatic pipelines and tools requires considerable bioinformatic expertise. These challenges have substantially limited the clinical translation of phage therapy.

FINDINGS

We have developed PhageGE (Phage Genome Explorer), a user-friendly graphical interface application for the interactive analysis of phage genomes. PhageGE enables users to perform key analyses, including phylogenetic analysis, visualization of phylogenetic trees, prediction of phage life cycle, and comparative analysis of phage genome annotations. The new R Shiny web server, PhageGE, integrates existing R packages and combines them with several newly developed functions to facilitate these analyses. Additionally, the web server provides interactive visualization capabilities and allows users to directly export publication-quality images.

CONCLUSIONS

PhageGE is a valuable tool that simplifies the analysis of phage genome data and may expedite the development and clinical translation of phage therapy. PhageGE is publicly available at https://jason-zhao.shinyapps.io/PhageGE_Update/.

Tackling the outer membrane: facilitating compound entry into Gram-negative bacterial pathogens

Emerging resistance to all available antibiotics highlights the need to develop new antibiotics with novel mechanisms of action. Most of the currently used antibiotics target Gram-positive bacteria while Gram-negative bacteria easily bypass the action of most drug molecules because of their unique outer membrane. This additional layer acts as a potent barrier restricting the entry of compounds into the cell. In this scenario, several approaches have been elucidated to increase the accumulation of compounds into Gram-negative bacteria. This review includes a brief description of the physicochemical properties that can aid compounds to enter and accumulate in Gram-negative bacteria and covers different strategies to target or bypass the outer membrane-mediated barrier in Gram-negative bacterial pathogens.

Discovery and druggability evaluation of pyrrolamide-type GyrB/ParE inhibitor against drug-resistant bacterial infection

The bacterial ATP-competitive GyrB/ParE subunits of type II topoisomerase are important anti-bacterial targets to treat super drug-resistant bacterial infections. Herein we discovered novel pyrrolamide-type GyrB/ParE inhibitors based on the structural modifications of the candidate AZD5099 that was withdrawn from the clinical trials due to safety liabilities such as mitochondrial toxicity. The hydroxyisopropyl pyridazine compound 28 had a significant inhibitory effect on Gyrase (GyrB, IC50 = 49 nmol/L) and a modest inhibitory effect on Topo IV (ParE, IC50 = 1.513 μmol/L) of Staphylococcus aureus. It also had significant antibacterial activities on susceptible and resistant Gram-positive bacteria with a minimum inhibitory concentration (MIC) of less than 0.03 μg/mL, which showed a time-dependent bactericidal effect and low frequencies of spontaneous resistance against S. aureus. Compound 28 had better protective effects than the positive control drugs such as DS-2969 (5) and AZD5099 (6) in mouse models of sepsis induced by methicillin-resistant Staphylococcus aureus (MRSA) infection. It also showed better bactericidal activities than clinically used vancomycin in the mouse thigh MRSA infection models. Moreover, compound 28 has much lower mitochondrial toxicity than AZD5099 (6) as well as excellent therapeutic indexes and pharmacokinetic properties. At present, compound 28 has been evaluated as a pre-clinical drug candidate for the treatment of drug-resistant Gram-positive bacterial infection. On the other hand, compound 28 also has good inhibitory activities against stubborn Gram-negative bacteria such as Escherichia coli (MIC = 1 μg/mL), which is comparable with the most potent pyrrolamide-type GyrB/ParE inhibitors reported recently. In addition, the structure-activity relationships of the compounds were also studied.

Synergistic effect of two antimicrobial peptides, BP203 and MAP-0403 J-2 with conventional antibiotics against colistin-resistant Escherichia coli and Klebsiella pneumoniae clinical isolates

Drug-resistant Enterobacterales infections are a great health concern due to the lack of effective treatments. Consequently, finding novel antimicrobials or combining therapies becomes a crucial approach in addressing this problem. BP203 and MAP-0403 J-2, novel antimicrobial peptides, have exhibited effectiveness against Gram-negative bacteria. In this study, we assessed the in vitro antibacterial activity of BP203 and MAP-0403 J-2, along with their synergistic interaction with conventional antibiotics including colistin, rifampicin, chloramphenicol, ceftazidime, meropenem, and ciprofloxacin against colistin-resistant Escherichia coli and Klebsiella pneumoniae clinical isolates. The minimal inhibitory concentrations (MIC) of BP203 and MAP-0403 J-2 against tested E. coli isolates were 2-16 and 8-32 μg/mL, respectively. However, for the majority of K. pneumoniae isolates, the MIC of BP203 and MAP-0403 J-2 were >128 μg/mL. Notably, our results demonstrated a synergistic effect when combining BP203 with rifampicin, meropenem, or chloramphenicol, primarily observed in most K. pneumoniae isolates. In contrast, no synergism was evident between BP203 and colistin, chloramphenicol, ceftazidime, rifampicin, or ciprofloxacin when tested against all E. coli isolates. Furthermore, synergistic effects between MAP-0403 J-2 and rifampicin, ceftazidime or colistin were observed against the majority of E. coli isolates. Similarly, the combined effect of MAP-0403 J-2 with rifampicin or chloramphenicol was synergistic in the majority of K. pneumoniae isolates. Importantly, these peptides displayed the stability at high temperatures, across a wide range of pH values, in specific serum concentrations and under physiological salt conditions. Both peptides also showed no significant hemolysis and cytotoxicity against mammalian cells. Our findings suggested that BP203 and MAP-0403 J-2 are promising candidates against colistin-resistant E. coli. Meanwhile, the synergism of these peptides and certain antibiotics could be of great therapeutic value as antimicrobial drugs against infections caused by colistin-resistant E. coli and K. pneumoniae.

Evaluation of Antibiotic Resistance Mechanisms in Gram-Negative Bacteria

Multidrug-resistant Gram-negative bacterial infections are exponentially increasing, posing one of the most urgent global healthcare and economic threats. Due to the lack of new therapies, the World Health Organization classified these bacterial species as priority pathogens in 2017, known as ESKAPE pathogens. This classification emphasizes the need for urgent research and development of novel targeted therapies. The majority of these priority pathogens are Gram-negative species, which possess a structurally dynamic cell envelope enabling them to resist multiple antibiotics, thereby leading to increased mortality rates. Despite 6 years having passed since the WHO classification, the progress in generating new treatment ideas has not been sufficient, and antimicrobial resistance continues to escalate, acting as a global ticking time bomb. Numerous efforts and strategies have been employed to combat the rising levels of antibiotic resistance by targeting specific resistance mechanisms. These mechanisms include antibiotic inactivating/modifying enzymes, outer membrane porin remodelling, enhanced efflux pump action, and alteration of antibiotic target sites. Some strategies have demonstrated clinical promise, such as the utilization of beta-lactamase inhibitors as antibiotic adjuvants, as well as recent advancements in machine-based learning employing artificial intelligence to facilitate the production of novel narrow-spectrum antibiotics. However, further research into an enhanced understanding of the precise mechanisms by which antibiotic resistance occurs, specifically tailored to each bacterial species, could pave the way for exploring narrow-spectrum targeted therapies. This review aims to introduce the key features of Gram-negative bacteria and their current treatment approaches, summarizing the major antibiotic resistance mechanisms with a focus on Escherichia coli, Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae. Additionally, potential directions for alternative therapies will be discussed, along with their relative modes of action, providing a future perspective and insight into the discipline of antimicrobial resistance.

Beyond antibiotics: phage-encoded lysins against Gram-negative pathogens

Antibiotics remain the frontline agents for treating deadly bacterial pathogens. However, the indiscriminate use of these valuable agents has led to an alarming rise in AMR. The antibiotic pipeline is insufficient to tackle the AMR threat, especially with respect to the WHO critical category of priority Gram-negative pathogens, which have become a serious problem as nosocomial and community infections and pose a threat globally. The AMR pandemic requires solutions that provide novel antibacterial agents that are not only effective but against which bacteria are less likely to gain resistance. In this regard, natural or engineered phage-encoded lysins (enzybiotics) armed with numerous features represent an attractive alternative to the currently available antibiotics. Several lysins have exhibited promising efficacy and safety against Gram-positive pathogens, with some in late stages of clinical development and some commercially available. However, in the case of Gram-negative bacteria, the outer membrane acts as a formidable barrier; hence, lysins are often used in combination with OMPs or engineered to overcome the outer membrane barrier. In this review, we have briefly explained AMR and the initiatives taken by different organizations globally to tackle the AMR threat at different levels. We bring forth the promising potential and challenges of lysins, focusing on the WHO critical category of priority Gram-negative bacteria and lysins under investigation for these pathogens, along with the challenges associated with developing them as therapeutics within the existing regulatory framework.

RND pump inhibition: in-silico and in-vitro study by Eugenol on clinical strain of E. coli and P. aeruginosa

Multidrug-resistant (MDR) gram-negative bacteria pose significant challenges to the public health. Various factors are involved in the development and spread of MDR strains, including the overuse and misuse of antibiotics, the lack of new antibiotics being developed, and etc. Efflux pump is one of the most important factors in the emergence of antibiotic resistance in bacteria. Aiming at the introduction of novel plant antibiotic, we investigated the effect of eugenol on the MexA and AcrA efflux pumps in Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli (E. coli). Molecular docking was performed using PachDock Server 1.3. The effect of eugenol on bacteria was determined by disk diffusion, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). A cartwheel test was also performed to evaluate efflux pump inhibition. Finally, the expression of the MexA and AcrA genes was examined by real-time PCR. The results of molecular docking showed that eugenol interacted with MexA and AcrA pumps at - 29.28 and - 28.59 Kcal.mol-1, respectively. The results of the antibiogram test indicated that the antibiotic resistance of the treated bacteria decreased significantly (p < 0.05). The results of the cartwheel test suggested the inhibition of efflux pump activity in P. aeruginosa and E. coli. Analysis of the genes by real-time PCR demonstrated that the expression of MexA and AcrA genes was significantly reduced, compared to untreated bacteria (p < 0.001). The findings suggest, among other things, that eugenol may make P. aeruginosa and E. coli more sensitive to antibiotics and that it could be used as an inhibitor to prevent bacteria from becoming resistant to antibiotics.

Zidovudine-β-Lactam Pronucleoside Strategy for Selective Delivery into Gram-Negative Bacteria Triggered by β-Lactamases

Addressing antibacterial resistance is a major concern of the modern world. The development of new approaches to meet this deadly threat is a critical priority. In this article, we investigate a new approach to negate bacterial resistance: exploit the β-lactam bond cleavage by β-lactamases to selectively trigger antibacterial prodrugs into the bacterial periplasm. Indeed, multidrug-resistant Gram-negative pathogens commonly produce several β-lactamases that are able to inactivate β-lactam antibiotics, our most reliable and widely used therapeutic option. The chemical structure of these prodrugs is based on a monobactam promoiety, covalently attached to the active antibacterial substance, zidovudine (AZT). We describe the synthesis of 10 prodrug analogues (5a-h) in four to nine steps and their biological activity. Selective enzymatic activation by a panel of β-lactamases is demonstrated, and subsequent structure-activity relationships are discussed. The best compounds are further evaluated for their activity on both laboratory strains and clinical isolates, preliminary stability, and toxicity.

Enterobacter cloacae as sole organism responsible for vertebral osteomyelitis/discitis and vertebral collapse in a patient with intravenous drug abuse

Staphylococcus aureus is the most commonly isolated organism in osteomyelitis, while gram-negative bacteria (GNB) comprises only a minor portion. GNB osteomyelitis is usually seen in patients with bacteraemia, recent genitourinary infection, open fractures or trauma and is rarely seen in the spines. Our case is a man in his 30s with no significant risk factors except an extended history of intravenous drug use (IVDU), who presented with back pain and subsequently developed vertebral collapse. Bone culture grew Enterobacter cloacae, yet blood cultures were negative. To date, there are limited data on the prevalence of GNB osteomyelitis in IVDU and its association. Due to rising rates of IVDU, further research must be done into associated medical complications to provide comprehensive care. Moreover, the emergence of multidrug-resistant GNB strains limits the number of effective antibiotics and is expected to pose more serious public concerns in the future.

Molecular Characteristics and Genetic Analysis of Extensively Drug-Resistant Isolates with different Tn3 Mobile Genetic Elements

Extensively drug-resistant (XDR) bacteria are the main caues for causing clinical infectious diseases. Our aim was to distinguish the present molecular epidemiological situation of XDR Klebsiella pneumoniae, Acinetobacter baumannii, and Escherichia coli isolates recovered from local hospitals in Changzhou. Antibiotic susceptibility and phenotypic analysis, multilocus sequence typing and Pulsed Field Gel Electrophoresis were performed to trace these isolates. Resistant phenotype and gene analysis from 29 XDR strains demonstrated that they mainly included TEM, CTX-M-1/2, OXA-48, and KPC products. A. baumannii strains belonged to sequence type (ST) ST224, and carrying the bla_CTX-M-2/TEM gene. The quinolone genes aac(6')-ib-cr and qnrB were carrying only in A. baumannii and E.coli. Three (2.3%) of these strains were found to contain the bla_NDM-1 or bla_NDM-5 gene. A new genotype of K. pneumoniae was found as ST2639. Epidemic characteristics of the XDR clones showed that antibiotic resistance genes distributed unevenly in different wards in Changzhou's local hospitals. With the sequencing of bla_NDM carrying isolates, the plasmids often carrying a highly conservative Tn3-relavent mobile genetic element. The especially coupled insert sequence ISKox3 may be a distinctive resistance gene transfer loci. The genotypic diversity variation of XDRs suggested that tracking and isolating the sources of antibiotic resistance especially MBL-encoding genes such as bla_NDM-will help manage the risk of infection by these XDRs.

PlyKp104, a Novel Phage Lysin for the Treatment of Klebsiella pneumoniae, Pseudomonas aeruginosa, and Other Gram-Negative ESKAPE Pathogens

Klebsiella pneumoniae and Pseudomonas aeruginosa are two leading causes of burn and wound infections, pneumonia, urinary tract infections, and more severe invasive diseases, which are often multidrug resistant (MDR) or extensively drug resistant. Due to this, it is critical to discover alternative antimicrobials, such as bacteriophage lysins, against these pathogens. Unfortunately, most lysins that target Gram-negative bacteria require additional modifications or outer membrane permeabilizing agents to be bactericidal. We identified four putative lysins through bioinformatic analysis of Pseudomonas and Klebsiella phage genomes in the NCBI database and then expressed and tested their intrinsic lytic activity in vitro. The most active lysin, PlyKp104, exhibited >5-log killing against K. pneumoniae, P. aeruginosa, and other Gram-negative representatives of the multidrug-resistant ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, K. pneumonia, Acinetobacter baumannii, P. aeruginosa, and Enterobacter species) without further modification. PlyKp104 displayed rapid killing and high activity over a wide pH range and in high concentrations of salt and urea. Additionally, pulmonary surfactants and low concentrations of human serum did not inhibit PlyKp104 activity in vitro. PlyKp104 also significantly reduced drug-resistant K. pneumoniae >2 logs in a murine skin infection model after one treatment of the wound, suggesting that this lysin could be used as a topical antimicrobial against K. pneumoniae and other MDR Gram-negative infections.

Reliability of E-Tests and the Phoenix Automated Method in Assessing Susceptibility to IV Fosfomycin-Comparative Studies Relative to the Reference Method

The agar dilution method (ADM) recommended for IV fosfomycin (IV FOS) is complex and labor-intensive. Keeping in mind the reality of everyday laboratory work, we have evaluated the agreement of IV FOS susceptibility results obtained using the E-test and the Phoenix system with the results obtained using the ADM.

MATERIALS AND METHODS

The tests were performed on 860 strains. To evaluate susceptibility to IV FOS, BioMerieux E-tests (bioMerieux, Warsaw, Poland), BD Phoenix panels (BD Phoenix, Sparks, MD, USA), and the ADM were used. Clinical interpretation was performed in accordance with EUCAST Guidance (v12.0, 2021). The significance of the E-test and the Phoenix was analyzed in relation to the ADM by defining categorical agreement (CA), major error (ME), and very major error (VME). Essential agreement (EA) has also been defined for the E-test. A method was considered reliable, in accordance with ISO 20776-2:2007, when CA and EA were above 89.9% and VME was <3%.

RESULTS

A categorical agreement of >98.9% was demonstrated between the E-test and the ADM for overall strains and for Echerichia coli, ESBL-producing Enterobacterales, and Staphylococcus aureus, while between the Phoenix and the ADM, a CA of >98.9% was shown only for Escherichia coli, Staphylococcus aureus, and Proteus spp. A very major error rate of <3% was obtained only for Staphylococcus aureus and MBL-producing Pseudomonas evaluated by both the E-test and the Phoenix. An essential agreement of >98.9% between the E-test and the ADM has not been demonstrated for any of the tested groups of strains. The Phoenix yielded more VMEs than the E-test (50 and 46, respectively). The highest VME rate was demonstrated using the Phoenix method for Enterobacter spp. (53.83%).

CONCLUSIONS

Both the E-test and the Phoenix have turned out to be reliable in assessing IV FOS susceptibility only for Staphylococcus aureus (CA > 89.9% and VME < 3%). For the remaining tested groups of strains and genera, the simultaneous high CA rate and low VME rate required by ISO were not achieved. Both methods fared particularly badly in detecting strains resistant to IV.

The Prevalence of Carbapenemase-Producing Microorganisms and Use of Novel Cephalosporins for the Treatment of Severe Infections Caused by Carbapenem-Resistant Gram-Negative Bacteria in a Pediatric Cardiac Intensive Care Unit

BACKGROUND

The spread of carbapenem-resistant organisms (CROs) is an increasingly serious threat globally, especially in vulnerable populations, such as intensive care unit (ICU) patients. Currently, the antibiotic options for CROs are very limited, particularly in pediatric settings. We describe a cohort of pediatric patients affected by CRO infections, highlighting the important changes in carbapenemase production in recent years and comparing the treatment with novel cephalosporins (N-CEFs) to Colistin-based regimens (COLI).

METHODS

All patients admitted to the cardiac ICU of the Bambino Gesù Children's Hospital in Rome during the 2016-2022 period with an invasive infection caused by a CRO were enrolled.

RESULTS

The data were collected from 42 patients. The most frequently detected pathogens were Pseudomonas aeruginosa (64%), Klebsiella pneumoniae (14%) and Enterobacter spp. (14%). Thirty-three percent of the isolated microorganisms were carbapenemase producers, with a majority of VIM (71%), followed by KPC (22%) and OXA-48 (7%). A total of 67% of patients in the N-CEF group and 29% of patients in the comparative group achieved clinical remission (p = 0.04).

CONCLUSION

The increase over the years of MBL-producing pathogens in our hospital is challenging in terms of therapeutic options. According to the present study, N-CEFs are a safe and effective option in pediatric patients affected by CRO infections.

Phentolamine Significantly Enhances Macrolide Antibiotic Antibacterial Activity against MDR Gram-Negative Bacteria

OBJECTIVES

Multidrug-resistant (MDR) Gram-negative bacterial infections have limited treatment options due to the impermeability of the outer membrane. New therapeutic strategies or agents are urgently needed, and combination therapies using existing antibiotics are a potentially effective means to treat these infections. In this study, we examined whether phentolamine can enhance the antibacterial activity of macrolide antibiotics against Gram-negative bacteria and investigated its mechanism of action.

METHODS

Synergistic effects between phentolamine and macrolide antibiotics were evaluated by checkerboard and time-kill assays and in vivo using a Galleria mellonella infection model. We utilized a combination of biochemical tests (outer membrane permeability, ATP synthesis, ΔpH gradient measurements, and EtBr accumulation assays) with scanning electron microscopy to clarify the mechanism of phentolamine enhancement of macrolide antibacterial activity against Escherichia coli.

RESULTS

In vitro tests of phentolamine combined with the macrolide antibiotics erythromycin, clarithromycin, and azithromycin indicated a synergistic action against E. coli test strains. The fractional concentration inhibitory indices (FICI) of 0.375 and 0.5 indicated a synergic effect that was consistent with kinetic time-kill assays. This synergy was also seen for Salmonella typhimurium, Klebsiella pneumoniae, and Actinobacter baumannii but not Pseudomonas aeruginosa. Similarly, a phentolamine/erythromycin combination displayed significant synergistic effects in vivo in the G. mellonella model. Phentolamine added singly to bacterial cells also resulted in direct outer membrane damage and was able to dissipate and uncouple membrane proton motive force from ATP synthesis that, resulted in enhanced cytoplasmic antibiotic accumulation via reduced efflux pump activity.

CONCLUSIONS

Phentolamine potentiates macrolide antibiotic activity via reducing efflux pump activity and direct damage to the outer membrane leaflet of Gram-negative bacteria both in vitro and in vivo.

Impact of short chain fatty acids (SCFAs) on antimicrobial activity of new β-lactam/β-lactamase inhibitor combinations and on virulence of Escherichia coli isolates

In a healthy gut microbiota, short chain fatty acids (SCFAs) are produced. The antibacterial action of SCFAs against intestinal pathogens makes them useful for ensuring the safety of food and human health. In this study, we aimed to assess the in vitro inhibitory activity of SCFAs, and to report, for the first time, their impact on the activity of new β-lactam/β-lactamase inhibitor combinations. The minimum inhibitory concentrations of acetic, propionic, and butyric acids were determined against E. coli clinical isolates recovered from gastrointestinal infections. Cefoperazone/sulbactam, ceftazidime/avibactam and cefepime/enmetazobactam are new β-lactam/β-lactamase inhibitor combinations that were studied for their combined therapeutic effects. Also, the effects of pH and concentration of SCFAs were evaluated on in vitro bacterial growth and expression of genes encoding for motility, adhesion, invasion, and biofilm formation. SCFAs were tested at concentrations of 12 mM at pH 7.4 (ileum-conditions), in addition to 60 mM and 123 mM, at pH 6.5 (colon-conditions). The tested SCFAs showed the same MIC (3750 μg ml-1 ≃ 60 mM) against all isolates. Furthermore, the addition of SCFAs to the tested β-lactam/β-lactamase inhibitor combinations greatly restored the susceptibility of the isolates. SCFAs had significant effect on bacterial growth and virulence in a pH and concentration-dependent manner; low ileal concentration potentiated E. coli growth, while higher colonic concentration significantly suppressed growth and down-regulated the expression of virulence genes (fliC, ipaH, FimH, BssS). Therefore, the significant inhibitory effect of colonic SCFAs on β-lactam/β-lactamase inhibitor combinations might lead to the development of promising treatment strategies.

Pseudomonas Bacteremia in a Tertiary Hospital and Factors Associated with Mortality

Pseudomonas aeruginosa is the third most commonly identified cause among gram-negative microorganisms causing bloodstream infection (BSI) and carries a very high mortality, higher than that by other gram-negative pathogens. The aim of the present study was to assess the epidemiological and microbiological characteristics of patients with BSI by Pseudomonas spp. in a tertiary hospital, characterize the resistance rates of different Pseudomonas strains to the most clinically relevant anti-microbials, estimate the mortality rate, and identify factors independently associated with mortality. In total, 540 cultures from 419 patients sent to the microbiology department of the hospital during the 8-year period of the study were positive. Patients had a median age of 66 years, and 262 (62.5%) were male. The blood culture was drawn in the ICU in 201 of the patients (48%). The infection was hospital-acquired in 329 patients (78.5%) and the median hospital day when the blood culture was drawn was 15, with a range of 0 to 267 days. Median duration of stay in the hospital was 36 days, hospital mortality was 44.2% (185 patients), and 30-day mortality was 29.6% (124 patients). The most commonly isolated Pseudomonas species were P. aeruginosa followed by P. putida and P. oryzihabitans. There was a statistically significant reduction of P. aeruginosa isolation relative to non-aeruginosa Pseudomonas species in the post-COVID-19 era. Antimicrobial resistance of P. aeruginosa in clinically relevant antimicrobials with anti-pseudomonal activity was similar before and after the onset of the COVID-19 pandemic with the exception of gentamicin and tobramycin, with P. aeruginosa being more susceptible to these two antimicrobials in the post-COVID-19 era. Rates of multi-drug resistant (MDR), extensively-drug resistant (XDR), and difficult-to-treat (DTR) P. aeruginosa isolation were lower after the onset of the COVID-19 pandemic, even though a carbapenem-focused antimicrobial stewardship program had been implemented in the meantime. Increased age, ICU-acquisition of BSI, and more days in the hospital when positive blood culture was drawn were positively associated with 30-day mortality of patients with Pseudomonas BSI. The fact that rates of MDR, XDR, and DTR P. aeruginosa isolation were lower late in the study period, with a carbapenem-focused antimicrobial stewardship intervention being implemented in the meantime, further increases the understanding that implementation of antimicrobial stewardship interventions may halt the increase in antimicrobial resistance noted previously.

In Vitro and In Vivo Development of a β-Lactam-Metallo-β-Lactamase Inhibitor: Targeting Carbapenem-Resistant Enterobacterales

β-lactams are the most prescribed class of antibiotics due to their potent, broad-spectrum antimicrobial activities. However, alarming rates of antimicrobial resistance now threaten the clinical relevance of these drugs, especially for the carbapenem-resistant Enterobacterales expressing metallo-β-lactamases (MBLs). Antimicrobial agents that specifically target these enzymes to restore the efficacy of last resort β-lactam drugs, that is, carbapenems, are therefore desperately needed. Herein, we present a cyclic zinc chelator covalently attached to a β-lactam scaffold (cephalosporin), that is, BP1. Observations from in vitro assays (with seven MBL expressing bacteria from different geographies) have indicated that BP1 restored the efficacy of meropenem to ≤ 0.5 mg/L, with sterilizing activity occurring from 8 h postinoculation. Furthermore, BP1 was nontoxic against human hepatocarcinoma cells (IC₅₀ > 1000 mg/L) and exhibited a potency of (K_iapp) 24.8 and 97.4 μM against Verona integron-encoded MBL (VIM-2) and New Delhi metallo β-lactamase (NDM-1), respectively. There was no inhibition observed from BP1 with the human zinc-containing enzyme glyoxylase II up to 500 μM. Preliminary molecular docking of BP1 with NDM-1 and VIM-2 sheds light on BP1's mode of action. In Klebsiella pneumoniae NDM infected mice, BP1 coadministered with meropenem was efficacious in reducing the bacterial load by >3 log₁₀ units' postinfection. The findings herein propose a favorable therapeutic combination strategy that restores the activity of the carbapenem antibiotic class and complements the few MBL inhibitors under development, with the ultimate goal of curbing antimicrobial resistance.

In vitro activity of cefiderocol against clinically important carbapenem non-susceptible Gram-negative bacteria from Saudi Arabia

OBJECTIVES

Cefiderocol is a novel catechol-substituted siderophore cephalosporin with broad-spectrum activity against Gram-negative pathogens. However, variation of its activity among carbapenemase producers from various regions and countries has been reported. Here, we checked the in vitro activity against Gram-negative carbapenem non-susceptible bacteria collected in Saudi Arabia.

METHODS

Cefiderocol MICs were determined using the iron-depleted cation-adjusted Mueller-Hinton broth and interpreted according to the Clinical and Laboratory Standards Institute guidelines. Isolates (n = 288) included carbapenemase-producing Escherichia coli (n = 46), Klebsiella pneumoniae (n = 98), Acinetobacter baumannii (n = 65), and Pseudomonas aeruginosa (n = 79) clinical isolates.

RESULTS

Cefiderocol inhibited 73.26% (211/288) of the isolates studied at concentrations of ≤ 4 mg/L. Cefiderocol inhibited all carbapenem-resistant A. baumannii isolates (65/65, 100%) producing OXA-23-like, OXA-24-like, and NDM, and nearly all P. aeruginosa isolates (75/79, 94.94%), including those producing VIM and NDM. In contrast, the carbapenemase-producing isolates from the Enterobacterales group demonstrated significantly higher MICs with only 53.06% (52/98) of K. pneumoniae and 41.3% (19/46) of E. coli isolates exhibiting MICs of ≤4 mg/L. Isolates showing elevated MICs (73/144, 50.69%) included NDM (20/29, 68.97%), NDM/OXA-48-like (34/59, 57.63%), OXA-48-like (18/52, 34.62%), and KPC (1/4, 25%) producers, thus showing no clear association with the production of serine-type or metallo-type carbapenemases. However, high cefiderocol MICs (≥ 32mg/L) were associated with isolates producing NDM, and in particular, among those coproducing the OXA-232-type enzyme.

CONCLUSIONS

Cefiderocol had excellent activity against multi-drug resistant non-fermenting Gram-negative pathogens. Reasons behind the high cefiderocol MICs in certain Enterobacterales isolates need further investigation.

Antibiofilm effect of melittin alone and in combination with conventional antibiotics toward strong biofilm of MDR-MRSA and -Pseudomonas aeruginosa

INTRODUCTION

Multidrug-resistant (MDR) pathogens are being recognized as a critical threat to human health if they can form biofilm and, in this sense, biofilm-forming MDR-methicillin resistant Staphylococcus aureus (MRSA) and -Pseudomonas aeruginosa strains are a worse concern. Hence, a growing body of documents has introduced antimicrobial peptides (AMPs) as a substitute candidate for conventional antimicrobial agents against drug-resistant and biofilm-associated infections. We evaluated melittin's antibacterial and antibiofilm activity alone and/or in combination with gentamicin, ciprofloxacin, rifampin, and vancomycin on biofilm-forming MDR-P. aeruginosa and MDR-MRSA strains.

METHODS

Antibacterial tests [antibiogram, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC)], anti-biofilm tests [minimum biofilm inhibition concentration (MBIC), and minimum biofilm eradication concentration (MBEC)], as well as synergistic antibiofilm activity of melittin and antibiotics, were performed. Besides, the influence of melittin alone on the biofilm encoding genes and the cytotoxicity and hemolytic effects of melittin were examined.

RESULTS

MIC, MBC, MBIC, and MBEC indices for melittin were in the range of 0.625-5, 1.25-10, 2.5-20, and 10-40 μg/ml, respectively. The findings found that the combination of melittin AMP with antibiotics was synergistic and fractional biofilm inhibitory concentration index (FBICi) for most tested concentrations was <0.5, resulting in a significant reduction in melittin, gentamicin, ciprofloxacin, vancomycin, and rifampin concentrations by 2-256.4, 2-128, 2-16, 4-64 and 4-8 folds, respectively. This phenomenon reduced the toxicity of melittin, whereby its synergist concentration required for biofilm inhibition did not show cytotoxicity and hemolytic activity. Our findings found that melittin decreased the expression of icaA in S. aureus and LasR in P. aeruginosa genes from 0.1 to 4.11 fold for icaA, and 0.11 to 3.7 fold for LasR, respectively.

CONCLUSION

Overall, the results obtained from our study show that melittin alone is effective against the strong biofilm of MDR pathogens and also offers sound synergistic effects with antibiotics without toxicity. Hence, combining melittin and antibiotics can be a potential candidate for further evaluation of in vivo infections by MDR pathogens.

SAR investigation and optimization of benzimidazole-based derivatives as antimicrobial agents against Gram-negative bacteria

Antibiotic-resistant bacteria represent a serious threat to modern medicine and human life. Only a minority of antibacterial agents are active against Gram-negative bacteria. Hence, the development of novel antimicrobial agents will always be a vital need. In an effort to discover new therapeutics against Gram-negative bacteria, we previously reported a structure-activity-relationship (SAR) study on 1,2-disubstituted benzimidazole derivatives. Compound III showed a potent activity against tolC-mutant Escherichia coli with an MIC value of 2 μg/mL, representing a promising lead for further optimization. Building upon this study, herein, 49 novel benzimidazole compounds were synthesized to investigate their antibacterial activity against Gram-negative bacteria. Our design focused on three main goals, to address the low permeability of our compounds and improve their cellular accumulation, to expand the SAR study to the unexplored ring C, and to optimize the lead compound (III) by modification of the methanesulfonamide moiety. Compounds (25a-d, 25f-h, 25k, 25l, 25p, 25r, 25s, and 26b) exhibited potent activity against tolC-mutant E. coli with MIC values ranging from 0.125 to 4 μg/mL, with compound 25d displaying the highest potency among the tested compounds with an MIC value of 0.125 μg/mL. As its predecessor, III, compound 25d exhibited an excellent safety profile without any significant cytotoxicity to mammalian cells. Time-kill kinetics assay indicated that 25d exhibited a bacteriostatic activity and significantly reduced E. coli JW55031 burden as compared to DMSO. Additionally, combination of 25d with colistin partially restored its antibacterial activity against Gram-negative bacterial strains (MIC values ranging from 4 to 16 μg/mL against E. coli BW25113, K. pneumoniae, A. baumannii, and P. aeruginosa). Furthermore, formulation of III and 25d as lipidic nanoparticles (nanocapsules) resulted in moderate enhancement of their antibacterial activity against Gram-negative bacterial strains (A. Baumannii, N. gonorrhoeae) and compound 25d demonstrated superior activity to the lead compound III. These findings establish compound 25d as a promising candidate for treatment of Gram-negative bacterial infections and emphasize the potential of nano-formulations in overcoming poor cellular accumulation in Gram-negative bacteria where further optimization and investigation are warranted to improve the potency and broaden the spectrum of our compounds.

Inhibition of Enzymatic Acetylation-Mediated Resistance to Plazomicin by Silver Ions

Plazomicin is a recent U.S. Food and Drug Administration (FDA)-approved semisynthetic aminoglycoside. Its structure consists of a sisomicin scaffold modified by adding a 2(S)-hydroxy aminobutyryl group at the N1 position and a hydroxyethyl substituent at the 6' position. These substitutions produced a molecule refractory to most aminoglycoside-modifying enzymes. The main enzyme within this group that recognizes plazomicin as substrate is the aminoglycoside 2'-N-acetyltransferase type Ia [AAC(2')-Ia], which reduces the antibiotic's potency. Designing formulations that combine an antimicrobial with an inhibitor of resistance is a recognized strategy to extend the useful life of existing antibiotics. We have recently found that several metal ions inhibit the enzymatic inactivation of numerous aminoglycosides mediated by the aminoglycoside 6'-N-acetyltransferase type Ib [AAC(6')-Ib]. In particular, Ag+, which also enhances the effect of aminoglycosides by other mechanisms, is very effective in interfering with AAC(6')-Ib-mediated resistance to amikacin. Here we report that silver acetate is a potent inhibitor of AAC(2')-Ia-mediated acetylation of plazomicin in vitro, and it reduces resistance levels of Escherichia coli carrying aac(2')-Ia. The resistance reversion assays produced equivalent results when the structural gene was expressed under the control of the natural or the blaTEM-1 promoters. The antibiotic effect of plazomicin in combination with silver was bactericidal, and the mix did not show significant toxicity to human embryonic kidney 293 (HEK293) cells.