Emerging Gram negative resistance to last-line antimicrobial agents fosfomycin, colistin and ceftazidime-avibactam – epidemiology, laboratory detection and treatment implications

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

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

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

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

IMPORTANCE

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

Enhancing the stability and therapeutic potential of the antimicrobial peptide Feleucin-K3 against Multidrug-Resistant a. Baumannii through rational utilization of a D-amino acid substitution strategy

Antimicrobial peptides (AMPs), which have a low probability of developing resistance, are considered the most promising antimicrobial agents for combating antibiotic resistance. Feleucin-K3 is an amphiphilic cationic AMP that exhibits broad-spectrum antimicrobial activity. In our previous research, the first phenylalanine residue was identified as the critical position affecting its biological activity. Here, a series of Feleucin-K3 analogs containing hydrophobic D-amino acids were developed, leveraging the low sensitivity of proteases to unnatural amino acids and the regulatory effect of hydrophobicity on antimicrobial activity. Among them, K-1dF, which replaced the phenylalanine of Feleucin-K3 with its enantiomer (D-phenylalanine), exhibited potent antimicrobial activity with a therapeutic index of 46.97 and MICs between 4 to 8 μg/ml against both sensitive and multidrug-resistant Acinetobacter baumannii. The introduction of D-phenylalanine increased the salt tolerance and serum stability of Feleucin-K3. Moreover, K-1dF displayed a rapid bactericidal effect, a low propensity to develop resistance, and a synergistic effect when combined with antibiotics. More importantly, it exhibited considerable or superior efficacy to imipenem against pneumonia and skin abscess infection. In brief, the K-1dF obtained by simple and effective modification strategy has emerged as a promising candidate antimicrobial agent for tackling multidrug-resistant Acinetobacter baumannii infections.

Bacteriology of endotracheal tube biofilms and antibiotic resistance: a systematic review

Bacteria commonly adhere to surfaces and produce polymeric material to encase the attached cells to form communities called biofilms. Within these biofilms, bacteria can appear to be many times more resistant to antibiotics or disinfectants. This systematic review explores the prevalence and microbial profile associated with biofilm production of bacteria isolated from endotracheal tubes and its associations with antimicrobial resistance. A comprehensive search was performed on databases PubMed, Embase, and Google Scholar for relevant articles published between 1st January 2000 and 31st December 2022. The relevant articles were exported to Mendeley Desktop 1.19.8 and screened by title and abstract, followed by full text screening based on the eligibility criteria of the study. Quality assessment of the studies was performed using the Newcastle-Ottawa Scale (NOS) customized for cross-sectional studies. Furthermore, the prevalence of antimicrobial resistance in biofilm-producers isolated from endotracheal tube specimens was investigated. Twenty studies encompassing 981 endotracheal tubes met the eligibility criteria. Pseudomonas spp. and Acinetobacter spp. were predominant isolates among the biofilm producers. These biofilms provided strong resistance against commonly used antibiotics. The highest resistance rate observed in Pseudomonas spp. was against fluoroquinolones whereas the least resistance was seen against piperacillin-tazobactam. A similar trend of susceptibility was observed in Acinetobacter spp. with a very high resistance rate against fluoroquinolones, third-generation cephalosporins and carbapenems. In conclusion, endotracheal tubes were associated with colonization by biofilm forming bacteria with varying levels of antimicrobial resistance. Biofilms may promote the occurrence of recalcitrant infections in endotracheal tubes which need to be managed with appropriate protocols and antimicrobial stewardship. Research focus should shift towards meticulous exploration of biofilm-associated infections to improve detection and management.

β-lactam-induced OMV release promotes polymyxin tolerance in Salmonella enterica sv. Typhi

The rise of multidrug-resistant bacteria is a global concern, leading to a renewed reliance on older antibiotics like polymyxins as a last resort. Polymyxins, cationic cyclic peptides synthesized nonribosomally, feature a hydrophobic acyl tail and positively charged residues. Their antimicrobial mechanism involves initial interaction with Gram-negative bacterial outer-membrane components through polar and hydrophobic interactions. Outer membrane vesicles (OMVs), nano-sized proteoliposomes secreted from the outer membrane of Gram-negative bacteria, play a crucial role in tolerating harmful molecules, including cationic peptides such as polymyxins. Existing literature has documented environmental changes' impact on modulating OMV properties in Salmonella Typhimurium. However, less information exists regarding OMV production and characteristics in Salmonella Typhi. A previous study in our laboratory showed that S. Typhi ΔmrcB, a mutant associated with penicillin-binding protein (PBP, a β-lactam antibiotic target), exhibited hypervesiculation. Consequently, this study investigated the potential impact of β-lactam antibiotics on promoting polymyxin tolerance via OMVs in S. Typhi. Our results demonstrated that sub-lethal doses of β-lactams increased bacterial survival against polymyxin B in S. Typhi. This phenomenon stems from β-lactam antibiotics inducing hypervesiculation of OMVs with higher affinity for polymyxin B, capturing and diminishing its biologically effective concentration. These findings suggest that β-lactam antibiotic use may inadvertently contribute to decreased polymyxin effectivity against S. Typhi or other Gram-negative bacteria, complicating the effective treatment of infections caused by these pathogens. This study emphasizes the importance of evaluating the influence of β-lactam antibiotics on the interaction between OMVs and other antimicrobial agents.

Synergistic effect of tryptamine-urea derivatives to overcome the chromosomally-mediated colistin resistance in Klebsiella pneumoniae

Colistin is considered as the last-resort antibiotics to treat multi-drug resistant Gram-negative bacterial infections in humans. However, the clinical use of colistin was limited because of the apparition of chromosomal mutations and mobile colistin resistance genes in bacterial isolates. One promising strategy is to combine existing antibiotics with promising non-antibiotics to overcome the widespread emergence of antibiotic-resistant pathogens. Moreover, colistin resistance would be regulated by two component systems PhoP/PhoQ which leads to permanent synthesis of cationic groups compensating for Mg2+ deficiency. In this study, the synthesis of a small library of tryptamine urea derivatives was carried out. In addition, antibiotic susceptibility, antibiotic adjuvant screening and checkerboard assays were used to investigate the antibacterial activity of these synthesized compounds and the potential synergistic activity of their combination with colistin. Conformational analysis of the docked binding modes of the active compound in the predicted binding pocket of bacterial response regulator PhoP were carried out, to see if the active compound inhibits PhoP which is involved in colistin resistance. Finally, hemolytic activity studies have been conducted on the most active compound.

Synergy with farnesol rejuvenates colistin activity against Colistin-resistant Gram-negative bacteria in vitro and in vivo

Colistin (COL) is considered the last line of treatment against infections due to multidrug-resistant (MDR) Gram-negative bacteria (GNB). However, the increasing number of colistin-resistant (COL-R) bacteria is a great threat to public health. In this study, a strategy of combining farnesol (FAR), which has anti-inflammatory and antitumor properties, with COL to restart COL activity was proposed. The synergistic effect of FAR combined with COL against COL-R GNB in vivo and in vitro were investigated. The excellent synergistic antibacterial activity of the COL-FAR combination was confirmed by performing the checkerboard assay, time-killing assay, and LIVE/DEAD bacterial cell viability assay. Crystal violet staining and scanning electron microscopy results showed that COL-FAR prevented biofilm formation and eradicated pre-existing mature biofilm. Cytotoxicity assay showed that FAR at 64 µg/mL was not cytotoxic to RAW264.7 cells. In vivo infection experiments showed that COL-FAR increased the survival rate of infected Galleria mellonella and decreased the bacterial load in a mouse thigh infection model. These results indicate that COL-FAR is a potentially effective therapeutic option for combating COL-R GNB infections.

An overview of colistin resistance: A breach in last line defense

Rising prevalence of antibiotic resistance and the unavailability of newer drugs to tackle this menace is one of the major hindrances to the goal of health and well-being set up by the General Assembly of the United Nations. The genes responsible for this resistance are often disseminated from hospitals to different environmental sources. In 2015, for the first time, resistance to Colistin was detected caused by chromosomal genetic mutations. Later, plasmid-mediated colistin resistance (MCR-1 to MCR-10) was detected, first from China and then from various other countries. As per Clinical and Laboratory Standards Institute (CLSI), commonly available diffusion techniques cannot detect colistin resistance appropriately. Even commercial susceptibility systems fail in this regard. Keeping in mind the importance of surveillance of colistin-resistant bugs, we present an update on the prevalence, mechanism of resistance, and detection.

Neonatal Bloodstream Infection with Ceftazidime-Avibactam-Resistant blaKPC-2-Producing Klebsiella pneumoniae Carrying blaVEB-25

BACKGROUND

Although ceftazidime/avibactam (CAZ/AVI) has become an important option for treating adults and children, no data or recommendations exist for neonates. We report a neonatal sepsis case due to CAZ/AVI-resistant blaKPC-2-harboring Klebsiella pneumoniae carrying blaVEB-25 and the use of a customized active surveillance program in conjunction with enhanced infection control measures.

METHODS

The index case was an extremely premature neonate hospitalized for 110 days that had been previously treated with multiple antibiotics. Customized molecular surveillance was implemented at hospital level and enhanced infection control measures were taken for early recognition and prevention of outbreak. Detection and identification of blaVEB-25 was performed using next-generation sequencing.

RESULTS

This was the first case of a bloodstream infection caused by KPC-producing K. pneumoniae that was resistant to CAZ/AVI without the presence of a metalo-β-lactamase in the multiplex PCR platform in a neonate. All 36 additional patients tested (12 in the same NICU and 24 from other hospital departments) carried wild-type blaVEB-1 but they did not harbor blaVEB-25.

CONCLUSION

The emergence of blaVEB-25 is signal for the horizontal transfer of plasmids at hospital facilities and it is of greatest concern for maintaining a sharp vigilance for the surveillance of novel resistance mechanisms. Molecular diagnostics can guide appropriate antimicrobial therapy and the early implementation of infection control measures against antimicrobial resistance.

Polymyxin combination therapy for multidrug-resistant, extensively-drug resistant, and difficult-to-treat drug-resistant gram-negative infections: is it superior to polymyxin monotherapy?

INTRODUCTION

The increasing prevalence of infections with multidrug-resistant (MDR), extensively-drug resistant (XDR) or difficult-to-treat drug resistant (DTR) Gram-negative bacilli (GNB), including Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae, Enterobacter species, and Escherichia coli poses a severe challenge.

AREAS COVERED

The rapid growing of multi-resistant GNB as well as the considerable deceleration in development of new anti-infective agents have made polymyxins (e.g. polymyxin B and colistin) a mainstay in clinical practices as either monotherapy or combination therapy. However, whether the polymyxin-based combinations lead to better outcomes remains unknown. This review mainly focuses on the effect of polymyxin combination therapy versus monotherapy on treating GNB-related infections. We also provide several factors in designing studies and their impact on optimizing polymyxin combinations.

EXPERT OPINION

An abundance of recent in vitro and preclinical in vivo data suggest clinical benefit for polymyxin-drug combination therapies, especially colistin plus meropenem and colistin plus rifampicin, with synergistic killing against MDR, XDR, and DTR P. aeruginosa, K. pneumoniae and A. baumannii. The beneficial effects of polymyxin-drug combinations (e.g. colistin or polymyxin B + carbapenem against carbapenem-resistant K. pneumoniae and carbapenem-resistant A. baumannii, polymyxin B + carbapenem + rifampin against carbapenem-resistant K. pneumoniae, and colistin + ceftolozan/tazobactam + rifampin against PDR-P. aeruginosa) have often been shown in clinical setting by retrospective studies. However, high-certainty evidence from large randomized controlled trials is necessary. These clinical trials should incorporate careful attention to patient's sample size, characteristics of patient's groups, PK/PD relationships and dosing, rapid detection of resistance, MIC determinations, and therapeutic drug monitoring.

Prevalence and molecular characteristics of polymyxin-resistant Enterobacterales in a Chinese tertiary teaching hospital

Introduction

Polymyxin-resistant Enterobacterales poses a significant threat to public health globally, but its prevalence and genomic diversity within a sole hospital is less well known. In this study, the prevalence of polymyxin-resistant Enterobacterales in a Chinese teaching hospital was investigated with deciphering of their genetic determinants of drug resistance.

Methods

Polymyxin-resistant Enterobacterales isolates identified by matrix-assisted laser desorption were collected in Ruijin Hospital from May to December in 2021. Both the VITEK 2 Compact and broth dilution methods were used to determine polymyxin B (PMB) susceptibility. Polymyxin-resistant isolates were further characterized by molecular typing using PCR, multi-locus sequence typing, and sequencing of the whole genome.

Results

Of the 1,216 isolates collected, 32 (2.6%) across 12 wards were polymyxin-resistant (minimum inhibitory concentration (MIC) range, PMB 4-256 mg/ml, and colistin 4 ≥ 16 mg/ ml). A total of 28 (87.5%) of the polymyxin-resistant isolates had reduced susceptibility to imipenem and meropenem (MIC ≥ 16 mg/ml). Of the 32 patients, 15 patients received PMB treatment and 20 survived before discharge. The phylogenetic tree of these isolates showed they belonged to different clones and had multiple origins. The polymyxin-resistant Klebsiella pneumoniae isolates belonged to ST-11 (85.72%), ST-15 (10.71%), and ST-65 (3.57%), and the polymyxin-resistant Escherichia coli belonged to four different sequence types, namely, ST-69 (25.00%), ST-38 (25.00%), ST-648 (25.00%), and ST-1193 (25.00%). In addition, six mgrB specific mutations (snp_ALT c.323T>C and amino acid change p.Val8Ala) were identified in 15.6% (5/32) of the isolates. mcr-1, a plasmid-mediated polymyxin-resistant gene, was found in three isolates, and non-synonymous mutations including T157P, A246T, G53V, and I44L were also observed.

Discussion

In our study, a low prevalence of polymyxin-resistant Enterobacterales was observed, but these isolates were also identified as multidrug resistant. Therefore, efficient infection control measures should be implemented to prevent the further spread of resistance to last-line polymyxin therapy.

Adverse Events and Drug Resistance in Critically Ill Patients Treated with Colistimethate Sodium: A Review of the Literature

The adverse events related to sodium colistimethate have had variability regarding the prevalence of nephrotoxicity, neurotoxicity, and less frequent respiratory depression. In recent years, its use has been relevant due to the increase of multidrug-resistant bacteria since it is considered the last-line drug, being its main adverse event and reason for discrepancies between authors' nephrotoxicity. The indiscriminate use of antibiotic therapy has generated multiple mechanisms of resistance, the most common being related to Colistin, the bactericidal escape effect. Based on the search criteria, no randomized clinical trials were identified showing safety and efficacy with the use of Colistin, inferring that the application of the appropriate dose is governed by expert opinion and retrospective and prospective observational studies, which confounding factors such as the severity of the patient and the predisposition to develop acute renal failure are constant. In this review, we focus on identifying the mechanism of nephrotoxicity and bacterial resistance, where much remains to be known.

New MraYAA Inhibitors with an Aminoribosyl Uridine Structure and an Oxadiazole

New inhibitors of the bacterial transferase MraY from Aquifex aeolicus (MraY_AA), based on the aminoribosyl uridine central core of known natural MraY inhibitors, have been designed to generate interaction of their oxadiazole linker with the key amino acids (H324 or H325) of the enzyme active site, as observed for the highly potent inhibitors carbacaprazamycin, muraymycin D2 and tunicamycin. A panel of ten compounds was synthetized notably thanks to a robust microwave-activated one-step sequence for the synthesis of the oxadiazole ring that involved the O-acylation of an amidoxime and subsequent cyclization. The synthetized compounds, with various hydrophobic substituents on the oxadiazole ring, were tested against the MraY_AA transferase activity. Although with poor antibacterial activity, nine out of the ten compounds revealed the inhibition of the MraY_AA activity in the range of 0.8 µM to 27.5 µM.

Molecular mechanisms and clonal lineages of colistin-resistant bacteria across the African continent: A scoping review

Colistin (also known as Polymyxin E), a polymyxin antibiotic discovered in the late 1940s, has recently reemerged as a last-line treatment option for multidrug-resistant infections. However, in recent years, colistin-resistant pathogenic bacteria have been increasingly reported worldwide. Accordingly, the presented review was undertaken to identify, integrate and synthesize current information regarding the detection and transmission of colistin-resistant bacteria across the African continent, in addition to elucidating their molecular mechanisms of resistance. PubMed, Google Scholar, and Science Direct were employed for study identification, screening and extraction. Overall, based on the developed literature review protocol and associated inclusion/exclusion criteria, 80 studies published between 2000 and 2021 were included comprising varying bacterial species and hosts. Numerous mechanisms of colistin resistance were reported, including chromosomal mutation(s) and transferable plasmid-mediated colistin resistance (encoded by mcr genes). Perhaps unexpectedly, mcr-variants have exhibited rapid emergence and spread across most African regions. The genetic variant mcr-1 is predominant in humans, animals, and the natural environment, and is primarily carried by IncHI2- type plasmid. The highest numbers of studies reporting the dissemination of colistin-resistant Gram-negative bacteria were conducted in the North African region.

Carbapenems consumption and Klebsiella resistance in intensive care units in Egypt: A study to evaluate the effect of an antimicrobial stewardship program

Background

The high prevalence of carbapenem-resistant Klebsiella imposes optimizing antibiotic consumption. We aimed to evaluate the impact of antibiotic stewardship program on carbapenem consumption and the Klebsiella resistance.

Method

We retrospectively evaluated critically ill patients with isolated Klebsiella species from Elaraby hospital, Egypt during the period from April 2017 to January 2019. We collected data related to carbapenems consumption and Klebsiella clinical isolates with their antimicrobial susceptibility. Based on susceptibility, Klebsiella isolates were classified into sensitive, extended spectrum beta-lactamase (ESBL) producer, and carbapenem-resistant Klebsiella (CRK), respectively. Our primary outcome was the change in carbapenems consumption after implementing the program, while the secondary outcomes were the changes in the incidence of CRK.

Results

The study included 205 patients with isolated Klebsiella species during the study period. The antibiotic stewardship program started in March 2018. Out of the 205 patients, 61 patients (29.8%) represented the pre-intervention sample, and 144 patients (70.2%) represented the post-intervention sample. Applying the antibiotic stewardship program was associated with a significant decrease in the carbapenems consumption from 38.9 to 26.6 defined daily dose/1000 patient-days (p = 0.02). The incidence of CRK was decreased from 85.25% of total Klebsiella isolates to 48.6% (p < 0.001). Klebsiella species were more likely to be in a lower category of resistance after applying the program with an odds ratio of 6.3 (2.88-13.73) using ordinal logistic regression.

Conclusion

Applying the antibiotic stewardship program could reduce the unnecessary carbapenems use in the ICU with a subsequent decrease in the emergence of the Klebsiella-resistant strains.

Prevalence and Molecular Characteristics of Polymyxin-Resistant Pseudomonas aeruginosa in a Chinese Tertiary Teaching Hospital

Polymyxin-resistant Pseudomonas aeruginosa is a major threat to public health globally. We investigated the prevalence of polymyxin-resistant P. aeruginosa in a Chinese teaching hospital and determined the genetic and drug-resistant phenotypes of the resistant isolates. P. aeruginosa isolates identified by MALDI-TOF MS were collected across a 3-month period in Ruijin Hospital. Antimicrobial susceptibility was determined by a Vitek-2 Compact system with broth dilution used to determine polymyxin B (PMB) susceptibility. Polymyxin-resistant isolates were further characterized by molecular typing using PCR, multi-locus sequence typing (MLST) and whole-genome sequencing. Phylogenetic relationships were analyzed using single nucleotide polymorphism (SNP) from the whole-genome sequencing. Of 362 P. aeruginosa isolates collected, 8 (2.2%) isolates from separate patients across six wards were polymyxin-resistant (MIC range, PMB 4–16 μg/mL and colistin 4–≥16 μg/mL). Four patients received PMB treatments (intravenous, aerosolized and/or topical) and all patients survived to discharge. All polymyxin-resistant isolates were genetically related and were assigned to five different clades (Isolate 150 and Isolate 211 being the same ST823 type). Genetic variations V51I, Y345H, G68S and R155H in pmrB and L71R in pmrA were identified, which might confer polymyxin resistance in these isolates. Six of the polymyxin-resistant isolates showed reduced susceptibility to imipenem and meropenem (MIC range ≥ 16 μg/mL), while two of the eight isolates were resistant to ceftazidime. We revealed a low prevalence of polymyxin-resistant P. aeruginosa in a Chinese teaching hospital with most polymyxin-resistant isolates being multidrug-resistant. Therefore, effective infection control measures are urgently needed to prevent further spread of resistance to the last-line polymyxins.

Durlobactam in the Treatment of Multidrug-Resistant Acinetobacter baumannii Infections: A Systematic Review

A. baumannii is a frequent cause of difficult-to-treat healthcare-associated infections. The use of a novel beta-lactamase inhibitor, durlobactam, has been proposed against multidrug-resistant A. baumannii. A systematic review of studies assessing the efficacy and safety of durlobactam in the treatment of multidrug-resistant A. baumannii infections was carried out. The study protocol was pre-registered on PROSPERO (CRD42022311723). Published articles on durlobactam were identified through computerized literature searches with the search terms "durlobactam" and "ETX2514" using PubMed. PubMed was searched until 15 February 2022. Articles providing data on the main characteristics of durlobactam and on the efficacy and safety of durlobactam in the treatment of A. baumannii infections were included in this systematic review. Attempt was made to obtain information about unpublished studies. English language restriction was applied. The risk of bias in the included studies was not assessed. Both quantitative and qualitative information were summarized by means of textual descriptions. Thirty studies on durlobactam were identified, published from June 2017 to November 2020. Sixteen studies met the inclusion criteria. Durlobactam is effective against A. baumannii when used in combination with sulbactam. Future clinical trials are needed to confirm the possibility to treat infections caused by multidrug-resistant A. baumannii with this combination.

Rescuing humanity by antimicrobial peptides against colistin-resistant bacteria

Abstract

It has been about a century since the discovery of the first antibiotic, and during this period, several antibiotics were produced and marketed. The production of high-potency antibiotics against infections led to victories, but these victories were temporary. Overuse and misuse of antibiotics have continued to the point that humanity today is almost helpless in the fight against infection. Researchers have predicted that by the middle of the new century, there will be a dark period after the production of antibiotics that doctors will encounter antibiotic-resistant infections for which there is no cure. Accordingly, researchers are looking for new materials with antimicrobial properties that will strengthen their ammunition to fight antibiotic-resistant infections. One of the most important alternatives to antibiotics introduced in the last three decades is antimicrobial peptides (AMPs), which affect a wide range of microbes. Due to their different antimicrobial properties from antibiotics, AMPs can fight and kill MDR, XDR, and colistin-resistant bacteria through a variety of mechanisms. Therefore, in this study, we intend to use the latest studies to give a complete description of AMPs, the importance of colistin-resistant bacteria, and their resistance mechanisms, and represent impact of AMPs on colistin-resistant bacteria.

Key points

• AMPs as limited options to kill colistin-resistant bacteria.

• Challenge of antibiotics resistance, colistin resistance, and mechanisms.

• What is AMPs in the war with colistin-resistant bacteria?

Antibiotic-loaded lipid-based nanocarrier: a promising strategy to overcome bacterial infection

According to the World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC), bacterial infections are one of the greatest threats to global health, food production, and life expectancy. In this sense, the development of innovative formulations aiming at greater therapeutic efficacy, safety, and shorter treatment duration compared to conventional products is urgently needed. Lipid-based nanocarriers (LBNs) have demonstrated the potential to enhance the effectiveness of available antibiotics. Among them, liposome, nanoemulsion, solid lipid nanoparticle (SLN), and nanostructured lipid carrier (NLC) are the most promising due to their solid technical background for laboratory and industrial production. This review describes recent advances in developing antibiotic-loaded LBNs against susceptible and resistant bacterial strains and biofilm. LBNs revealed to be a promising alternative to deliver antibiotics due to their superior characteristics compared to conventional preparations, including their modified drug release, improved bioavailability, drug protection against chemical or enzymatic degradation, greater drug loading capacity, and biocompatibility. Antibiotic-loaded LBNs can improve current clinical drug therapy, bring innovative products and rescue discarded antibiotics. Thus, antibiotic-loaded LBNs have potential to open a window of opportunities to continue saving millions of lives and prevent the devastating impact of bacterial infection.

ICU-Associated Gram-Negative Bloodstream Infection: Risk Factors Affecting the Outcome Following the Emergence of Colistin-Resistant Isolates in a Regional Greek Hospital

Intensive care unit patients may present infections by difficult-to-treat-resistant Gram-negative microorganisms. Colistin resurfaced as a last resort antibiotic for the treatment of multi-drug-resistant Gram-negative bacteria. However, colistin might not improve survival, particularly after the emergence of colistin-resistant isolates. We aimed to (1) examine the first Gram-negative-associated-bloodstream infection (GN-BSI) effect on 28-day mortality and (2) distinguish mortality risk factors. From 1 January 2018 to 31 December 2019, we retrospectively studied all adult patients admitted for more than 48 h in the critical care department of a regional Greek hospital, with prevalent difficult-to-treat Gram-negative pathogens. We examined the patient records for the first GN-BSI. The local laboratory used broth microdilution to evaluate bacterial susceptibility to colistin. Seventy-eight patients fulfilled the entry criteria: adult and first GN-BSI. They developed GN-BSI on day 10 (6–18), while the overall mortality was 26.9%. Thirty-two and 46 individuals comprised the respective colistin-resistant and colistin-sensitive groups. The admission Acute Physiology Assessment and Chronic Health Evaluation II score was associated with acquiring colistin-resistant GN-BSI in the multivariable logistic regression analysis (οdds ratio (CI), 1.11 (1.03–1.21)). Regarding mortality, the index day sequential organ failure assessment score was solely associated with the outcome (hazard-ratio (CI), 1.23 (1.03–1.48), Cox proportional hazard analysis). GN-BSI was often caused by colistin-resistant bacteria. Concerning our data, sepsis severity was the independent predictor of mortality regardless of the colistin-resistance phenotype or empirical colistin treatment.

A Sub-Micromolar MraYAA Inhibitor with an Aminoribosyl Uridine Structure and a (S,S)-Tartaric Diamide: Synthesis, Biological Evaluation and Molecular Modeling

New inhibitors of the bacterial tranferase MraY are described. Their structure is based on an aminoribosyl uridine scaffold, which is known to be important for the biological activity of natural MraY inhibitors. A decyl alkyl chain was introduced onto this scaffold through various linkers. The synthesized compounds were tested against the MraY_AA transferase activity, and the most active compound with an original (S,S)-tartaric diamide linker inhibits MraY activity with an IC₅₀ equal to 0.37 µM. Their antibacterial activity was also evaluated on a panel of Gram-positive and Gram-negative strains; however, the compounds showed no antibacterial activity. Docking and molecular dynamics studies revealed that this new linker established two stabilizing key interactions with N190 and H325, as observed for the highly potent inhibitors carbacaprazamycin, muraymycin D2 and tunicamycin.

Phenotypic Changes Associated With In Vivo Evolution of Colistin Resistance in ST11 Carbapenem-Resistant Klebsiella pneumoniae

Colistin is one of the few antibiotics that exhibit bactericidal effect on carbapenemase-producing Klebsiella pneumoniae strains. In recent years, however, colistin resistance is increasingly being reported among clinical carbapenem-resistant K. pneumoniae strains worldwide, posing serious challenge to treatment of infections caused by these organisms. In this study, we investigated one colistin-susceptible (YJH4) and one colistin-resistant (YJH15) K. pneumoniae strain, which were collected from a patient before and after colistin treatment, respectively. We characterized the effects of mgrB inactivation-induced colistin resistance on the physiological fitness and virulence in ST11 carbapenem-resistant K. pneumoniae both in vitro and in vivo. The colistin-resistant strain YJH15 was found to exhibit increased fitness and biofilm formation potential in vitro, and increased survival rate in the presence of normal human serum. Interestingly, YJH15 exhibited reduced virulence in the mouse infection model but enhanced virulence in Galleria mellonella infection model when compared to the colistin-susceptible parental strain YJH4. Infection with YJH15 was also found to result in lower expression level of inflammatory cytokine IL-1β in blood and significantly decreased bacterial loads in heart, liver, spleen, lung, kidney and blood. These results demonstrated that mgrB inactivation-induced colistin resistance has significant effects on multiple fitness and virulence-associated traits in K. pneumoniae.

In Vitro Screening of a 1280 FDA-Approved Drugs Library against Multidrug-Resistant and Extensively Drug-Resistant Bacteria

Alternative strategies against multidrug-resistant (MDR) bacterial infections are suggested to clinicians, such as drug repurposing, which uses rapidly available and marketed drugs. We gathered a collection of MDR bacteria from our hospital and performed a phenotypic high-throughput screening with a 1280 FDA-approved drug library. We used two Gram positive (Enterococcus faecium P5014 and Staphylococcus aureus P1943) and six Gram negative (Acinetobacter baumannii P1887, Klebsiella pneumoniae P9495, Pseudomonas aeruginosa P6540, Burkholderia multivorans P6539, Pandoraea nosoerga P8103, and Escherichia coli DSM105182 as the reference and control strain). The selected MDR strain panel carried resistance genes or displayed phenotypic resistance to last-line therapies such as carbapenems, vancomycin, or colistin. A total of 107 compounds from nine therapeutic classes inhibited >90% of the growth of the selected Gram negative and Gram positive bacteria at a drug concentration set at 10 µmol/L, and 7.5% were anticancer drugs. The common hit was the antiseptic chlorhexidine. The activity of niclosamide, carmofur, and auranofin was found against the selected methicillin-resistant S. aureus. Zidovudine was effective against colistin-resistant E. coli and carbapenem-resistant K. pneumoniae. Trifluridine, an antiviral, was effective against E. faecium. Deferoxamine mesylate inhibited the growth of XDR P. nosoerga. Drug repurposing by an in vitro screening of a drug library is a promising approach to identify effective drugs for specific bacteria.

Clinically healthy household dogs and cats as carriers of multidrug-resistant Salmonella enterica with variable R plasmids

Introduction. Antimicrobial resistance (AMR) is a One Health issue concerning humans, animals and the environment and a unified One Health approach is required to contain this problematic issue. Dogs and cats are popular pet animals and are known to carry many bacterial pathogens that are of public health importance, including Salmonella . However, data on AMR in companion animals is limited.

Gap statement. Scant AMR data from bacteria originating from companion animals limits an accurate assessment of the impacts of pet-animal-related AMR on public health.

Purpose. This study aimed to phenotypically and genetically investigate AMR in Salmonella isolated from pet dogs and cats in Thailand.

Methodology. Salmonella enterica were isolated from pet dogs (n=159) and cats (n=19) in Thailand between 2016 and 2019. All isolates were serotyped. Phenotypic and genotypic antimicrobial resistance was examined. PCR-based replicon typing, replicon sequence typing and plasmid multilocus sequence typing were conducted to characterize plasmids.

Results. Seventy-seven serovars were identified, with serovars Weltevreden (9.6%) and Stockholm (9.0%) the most common. Most of the isolates (34.3%) were multidrug-resistant. The serovar Stockholm was an ESBL-producer and carried the β-lactamase genes bla TEM-1 and bla CTX-M-55. The plasmid-mediated quinolone resistance (PMQR) gene, qnrS, was also detected (10.1%). Class 1 integrons carrying the dfrA12-aadA2 cassette array were most frequent (45.9%). Five plasmid replicon types as IncA/C (0.6%), N (1.1%), IncFIIA (28.7%), IncHI1 (2.2%), and IncI1 (3.4%) were identified. Based on the pMLST typing scheme (n=9), plasmids were assigned into five different STs including IncA/C-ST6 (n=1), IncH1-ST16 (n=4), IncI1-ST3 (n=1), IncI1-ST60 (n=1) and IncI1-ST136 (n=1). The ST 16 of IncHI1 plasmid was a novel plasmid ST. Subtyping F-type plasmids using the RST scheme (n=9) revealed four different combinations of replicons including S1:A-:B- (n=4), S1:A-:B22 (n=2), S3:A-:B- (n=1) and S-:A-:B47 (n=1).

Conclusions. Our findings highlight the role of clinically healthy household dogs and cats as carriers of AMR Salmonella strains with different R plasmid. The implementation of AMR phenotypes instigation and genotypic monitoring and surveillance programmes in companion animals are imperative as integral components of the One Health framework.

Investigation of In-vitro Efficacy of Intravenous Fosfomycin in Extensively Drug-Resistant Klebsiella pneumoniae Isolates and Effect of Glucose 6-Phosphate on Sensitivity Results

BACKGROUND

The aim of this study was to determine the in vitro efficacy of intravenous (IV) fosfomycin against extensively drug-resistant Enterobacterales strains and the effect of glucose 6-phosphate (G6-P) on sensitivity results.

MATERIAL METHOD

Thirty-two extensively drug-resistant Klebsiella pneumonia strains were included in the study. Detection of the carbapenemase genes was performed using the Gene-Xpert® System Carba R® kit. Susceptibility of IV fosfomycin was assessed using the agar dilution method. The agar dilution method was repeated using Muller-Hinton Agar medium without G6-P to assess the effect of G6-P on sensitivity results.

RESULTS

All strains in the study produced carbapenemases and were resistant to all drugs tested, including carbapenems, piperacillin-tazobactam, ceftriaxone, and ceftazidime. Fosfomycin resistance was detected in 3 (9.3%) strains. When the sensitivity test was repeated without G6-P, fosfomycin resistance was detected in 82.7% of the fosfomycin-susceptible strains. The Gene-Xpert® System showed NDM-1 in 46.8%, OXA-48 in 18.7%, KPC in 3.1%, and NDM-1 + OXA-48 in 21.8% of the strains. OXA-48 was detected in one of the resistant strains, and none of the viable genes were detected in two of the resistant strains.

CONCLUSION

This study shows that IV fosfomycin is a potentially important treatment alternative for infections caused by common resistant strains. Accurate results may not be obtained unless G6-P is used in the agar dilution method for in vitro susceptibility studies of fosfomycin.

Rapid Identification of Escherichia coli Colistin-Resistant Strains by MALDI-TOF Mass Spectrometry

Colistin resistance is one of the major threats for global public health, requiring reliable and rapid susceptibility testing methods. The aim of this study was the evaluation of a MALDI-TOF mass spectrometry (MS) peak-based assay to distinguish colistin resistant (colR) from susceptible (colS) Escherichia coli strains. To this end, a classifying algorithm model (CAM) was developed, testing three different algorithms: Genetic Algorithm (GA), Supervised Neural Network (SNN) and Quick Classifier (QC). Among them, the SNN- and GA-based CAMs showed the best performances: recognition capability (RC) of 100% each one, and cross validation (CV) of 97.62% and 100%, respectively. Even if both algorithms shared similar RC and CV values, the SNN-based CAM was the best performing one, correctly identifying 67/71 (94.4%) of the E. coli strains collected: in point of fact, it correctly identified the greatest number of colS strains (42/43; 97.7%), despite its lower ability in identifying the colR strains (15/18; 83.3%). In conclusion, although broth microdilution remains the gold standard method for testing colistin susceptibility, the CAM represents a useful tool to rapidly screen colR and colS strains in clinical practice.

Bacteriophage as a Novel Therapeutic Weapon for Killing Colistin-Resistant Multi-Drug-Resistant and Extensively Drug-Resistant Gram-Negative Bacteria

Colistin-resistant multidrug-resistant (MDR), extensively drug-resistant (XDR), and pan-drug-resistant (PDR) bacteria are highly lethal and many researchers have tried hard to combat these microorganisms around the world. Infections caused by these bacteria are resistant to the last resort of antibiotic therapy and have posed a major challenge in clinical and public health. Since the production of new antibiotics is very expensive and also very slow compared to the increasing rate of antibiotic resistance, researchers are suggesting the use of natural substances with high antibacterial potential. Bacteriophages are one of the most effective therapeutic measures that are known to exist for use for incurable and highly resistant infections. Phages are highly taken into consideration due to the lack of side effects, potential spread to various body organs, distinct modes of action from antibiotics, and proliferation at the site of infection. Although the effects of phages on MDR and XDR bacteria have been demonstrated in various studies, only a few have investigated the effect of phage therapy on colistin-resistant isolates. Therefore, in this review, we discuss the problems caused by colistin-resistant MDR and XDR bacteria in the clinics, explain the different mechanisms associated with colistin resistance, introduce bacteriophage therapy as a powerful remedy, and finally present new studies that have used bacteriophages against colistin-resistant isolates.

Current Update on Intrinsic and Acquired Colistin Resistance Mechanisms in Bacteria

Colistin regained global interest as a consequence of the rising prevalence of multidrug-resistant Gram-negative Enterobacteriaceae. In parallel, colistin-resistant bacteria emerged in response to the unregulated use of this antibiotic. However, some Gram-negative species are intrinsically resistant to colistin activity, such as Neisseria meningitides, Burkholderia species, and Proteus mirabilis. Most identified colistin resistance usually involves modulation of lipid A that decreases or removes early charge-based interaction with colistin through up-regulation of multistep capsular polysaccharide expression. The membrane modifications occur by the addition of cationic phosphoethanolamine (pEtN) or 4-amino-l-arabinose on lipid A that results in decrease in the negative charge on the bacterial surface. Therefore, electrostatic interaction between polycationic colistin and lipopolysaccharide (LPS) is halted. It has been reported that these modifications on the bacterial surface occur due to overexpression of chromosomally mediated two-component system genes (PmrAB and PhoPQ) and mutation in lipid A biosynthesis genes that result in loss of the ability to produce lipid A and consequently LPS chain, thereafter recently identified variants of plasmid-borne genes (mcr-1 to mcr-10). It was hypothesized that mcr genes derived from intrinsically resistant environmental bacteria that carried chromosomal pmrC gene, a part of the pmrCAB operon, code three proteins viz. pEtN response regulator PmrA, sensor kinase protein PmrAB, and phosphotransferase PmrC. These plasmid-borne mcr genes become a serious concern as they assist in the dissemination of colistin resistance to other pathogenic bacteria. This review presents the progress of multiple strategies of colistin resistance mechanisms in bacteria, mainly focusing on surface changes of the outer membrane LPS structure and other resistance genetic determinants. New handier and versatile methods have been discussed for rapid detection of colistin resistance determinants and the latest approaches to revert colistin resistance that include the use of new drugs, drug combinations and inhibitors. Indeed, more investigations are required to identify the exact role of different colistin resistance determinants that will aid in developing new less toxic and potent drugs to treat bacterial infections. Therefore, colistin resistance should be considered a severe medical issue requiring multisectoral research with proper surveillance and suitable monitoring systems to report the dissemination rate of these resistant genes.

Selective Bacterial Targeting and Infection-Triggered Release of Antibiotic Colistin Conjugates

In order to render potent, but toxic antibiotics more selective, we have explored a novel conjugation strategy that includes drug accumulation followed by infection-triggered release of the drug. Bacterial targeting was achieved using a modified fragment of the human antimicrobial peptide ubiquicidin, as demonstrated by fluorophore-tagged variants. To limit the release of the effector colistin only to infection-related situations, we introduced a linker that was cleaved by neutrophil elastase (NE), an enzyme secreted by neutrophil granulocytes at infection sites. The linker carried an optimized sequence of amino acids that was required to assure sufficient cleavage efficiency. The antibacterial activity of five regioisomeric conjugates prepared by total synthesis was masked, but was released upon exposure to recombinant NE when the linker was attached to amino acids at the 1- or the 3-position of colistin. A proof-of-concept was achieved in co-cultures of primary human neutrophils and Escherichia coli that induced the secretion of NE, the release of free colistin, and an antibacterial efficacy that was equal to that of free colistin.

Emergence of Multidrug-Resistant Escherichia coli Producing CTX-M, MCR-1, and FosA in Retail Food From Egypt

In this study, multidrug-resistant (MDR) Escherichia coli isolates from retail food and humans assigned into similar Multilocus Sequence Types (MLST) were analyzed using whole genome sequencing (WGS). In silico analysis of assembled sequences revealed the existence of multiple resistance genes among the examined E. coli isolates. Of the six CTX-M-producing isolates from retail food, bla _CTX-M-14 was the prevalent variant identified (83.3%, 5/6). Two plasmid-mediated fosfomycin resistance genes, fosA3, and fosA4, were detected from retail food isolates (one each from chicken and beef), where fosA4 was identified in the chicken isolate 82CH that also carried the colistin resistance gene mcr-1. The bla _CTX-M-14 and fosA genes in retail food isolates were located adjacent to insertion sequences ISEcp1 and IS26, respectively. Sequence analysis of the reconstructed mcr-1 plasmid (p82CH) showed 96-97% identity to mcr-1-carrying IncI2 plasmids previously identified in human and food E. coli isolates from Egypt. Hierarchical clustering of core genome MLST (HierCC) revealed clustering of chicken isolate 82CH, co-harboring mcr-1 and fosA4 genes, with a chicken E. coli isolate from China at the HC200 level (≤200 core genome allelic differences). As E. coli co-harboring mcr-1 and fosA4 genes has only been recently reported, this study shows rapid spread of this genotype that shares similar genetic structures with regional and international E. coli lineages originating from both humans and food animals. Adopting WGS-based surveillance system is warranted to facilitate monitoring the international spread of MDR pathogens.

Dual Function Antimicrobial Loaded Lectin Carrier: A Strategy to Overcome Biomolecular Interference without Detectable Resistance

The disposition of a drug in a biological system may be altered by complex biological fluids; especially, protein binding to drugs influences their activity. Herein, we demonstrated a convenient method involving the noncovalent formulation of butea monosperma seed lectin (BMSL) with an antimicrobial lipid, cationic N-acylethanolamine (cNAE) to mitigate the serum protein interference. Fluorescence spectroscopy and molecular docking study revealed that cNAEs readily formed noncovalent complexes with serum protein, bovine serum albumin. The resulting complexes interfered with the antimicrobial activity of cNAEs. Strikingly, the noncovalent conjugates developed with BMSL and cNAEs (BcNAE) overcame the interference from serum protein and displayed remarkable antimicrobial activity against uropathogenic Escherichia coli (UPEC). Strikingly, the minimum inhibitory concentration (MIC) of the lectin conjugates (7.81 μM) was 4-fold lower than the MIC of pure cNAE. Mechanistic studies showed that BcNAE depolarized the bacterial membrane and affected the integrity to exert the antimicrobial activity. The membrane directed activities of BcNAE on UPEC efficiently eliminated the development of resistance even after 25 passages. The hemocompatibility results and the biosafety assessed in a zebrafish model suggested that BcNAE was nontoxic with good selectivity to bacteria. While testing the therapeutic efficacy against UPEC infected zebrafish, we found that 1× MIC cNAE is ineffective due to interference from biological fluids, which is in agreement with in vitro studies. Remarkably, the infected fish treated with 1× MIC BcNAE conjugates were rescued from infection and restored to the normal life in less than 9 h. Bacterial colony count assay revealed that BcNAE was more efficient in overcoming the biological fluid interference and eliminated the bacterial burden in infected zebrafish. Histopathology analysis supported that BcNAE treatment restored the pathological changes induced by UPEC and, thus, increased survival. The high antimicrobial intensity with limited chance for resistance development and potential to overcome biomolecular interference with a lack of toxicity enhance the merits of exploring lectin conjugates against infectious pathogens.

Gene Expression Profiling of Pseudomonas aeruginosa Upon Exposure to Colistin and Tobramycin

Pseudomonas aeruginosa (Pae) is notorious for its high-level resistance toward clinically used antibiotics. In fact, Pae has rendered most antimicrobials ineffective, leaving polymyxins and aminoglycosides as last resort antibiotics. Although several resistance mechanisms of Pae are known toward these drugs, a profounder knowledge of hitherto unidentified factors and pathways appears crucial to develop novel strategies to increase their efficacy. Here, we have performed for the first time transcriptome analyses and ribosome profiling in parallel with strain PA14 grown in synthetic cystic fibrosis medium upon exposure to polymyxin E (colistin) and tobramycin. This approach did not only confirm known mechanisms involved in colistin and tobramycin susceptibility but revealed also as yet unknown functions/pathways. Colistin treatment resulted primarily in an anti-oxidative stress response and in the de-regulation of the MexT and AlgU regulons, whereas exposure to tobramycin led predominantly to a rewiring of the expression of multiple amino acid catabolic genes, lower tricarboxylic acid (TCA) cycle genes, type II and VI secretion system genes and genes involved in bacterial motility and attachment, which could potentially lead to a decrease in drug uptake. Moreover, we report that the adverse effects of tobramycin on translation are countered with enhanced expression of genes involved in stalled ribosome rescue, tRNA methylation and type II toxin-antitoxin (TA) systems.

Global research activity on antimicrobial resistance in food-producing animals

BACKGROUND

Antimicrobial resistance (AMR) is a global challenge that requires a "One Health" approach to achieve better public health outcomes for people, animals, and the environment. Numerous bibliometric studies were published on AMR in humans. However, none was published in food-producing animals. The current study aimed at assessing and analyzing scientific publications on AMR in food-producing animals.

METHOD

A validated search query was developed and entered in Scopus advanced search function to retrieve and quantitatively analyze relevant documents. Bibliometric indicators and mapping were presented. The study period was from 2000 to 2019.

RESULTS

The search query retrieved 2852 documents. During the period from 2015 to 2019, approximately 48% of the retrieved documents were published. The article about the discovery of plasmid-mediated colistin resistance in pigs received the highest number of citations (n = 1970). The Journal of Food Protection (n = 123; 4.3%) ranked first in the number of publications while the Applied and Environmental Microbiology journal ranked first in the number of citations per document. The USA led with 576 (20.2%) documents followed by China (n = 375; 13.1%). When the number of publications was standardized by income and population size, India (n = 51.5) ranked first followed by China (n = 38.3) and Brazil (n = 13.4). The growth of publications from China exceeded that of the USA in the last 3 years of the study period. Research collaboration in this field was inadequate. Mapping author keywords showed that E. coli, Salmonella, poultry, Campylobacter, chicken, cattle, and resistant genes were most frequent. The retrieved documents existed in five research themes. The largest research theme was about AMR in Salmonella in food-producing animals. The most recent research theme was about the dissemination and molecular transfer of AMR genes into the environment and among different bacterial strains.

CONCLUSION

Hot spots of research on AMR in food-producing animals match the world regions of reported hot spots of AMR in animals. Research collaboration in this field is of great importance, especially with low- and middle-income countries. Data on AMR need to be collected nationally and internationally to implement the "One Health" approach in the fight against AMR.

Assessing Upstream Determinants of Antibiotic Use in Small-Scale Food Animal Production through a Simulated Client Method

Small-scale food animal production has been celebrated as a means of economic mobility and improved food security but the use of veterinary antibiotics among these producers may be contributing to the spread of antibiotic resistance in animals and humans. In order to improve antibiotic stewardship in this sector, it is critical to identify the drivers of producers’ antibiotic use. This study assessed the determinants of antibiotic use in small-scale food animal production through simulated client visits to veterinary supply stores and surveys with households that owned food animals (n = 117) in Ecuador. Eighty percent of households with food animals owned chickens and 78% of those with chickens owned fewer than 10 birds. Among the households with small-scale food animals, 21% reported giving antibiotics to their food animals within the last six months. Simulated client visits indicated that veterinary sales agents frequently recommended inappropriate antibiotic use, as 66% of sales agents recommended growth promoting antibiotics, and 48% of sales agents recommended an antibiotic that was an inappropriate class for disease treatment. In contrast, few sales agents (3%) were willing to sell colistin, an antibiotic banned for veterinary use in Ecuador as of January 2020, which supports the effectiveness of government regulation in antibiotic stewardship. The cumulative evidence provided by this study indicates that veterinary sales agents play an active role in promoting indiscriminate and inappropriate use of antibiotics in small-scale food animal production.

Colistin and its role in the Era of antibiotic resistance: an extended review (2000-2019)

Increasing antibiotic resistance in multidrug-resistant (MDR) Gram-negative bacteria (MDR-GNB) presents significant health problems worldwide, since the vital available and effective antibiotics, including; broad-spectrum penicillins, fluoroquinolones, aminoglycosides, and β-lactams, such as; carbapenems, monobactam, and cephalosporins; often fail to fight MDR Gram-negative pathogens as well as the absence of new antibiotics that can defeat these "superbugs". All of these has prompted the reconsideration of old drugs such as polymyxins that were reckoned too toxic for clinical use. Only two polymyxins, polymyxin E (colistin) and polymyxin B, are currently commercially available. Colistin has re-emerged as a last-hope treatment in the mid-1990s against MDR Gram-negative pathogens due to the development of extensively drug-resistant GNB. Unfortunately, rapid global resistance towards colistin has emerged following its resurgence. Different mechanisms of colistin resistance have been characterized, including intrinsic, mutational, and transferable mechanisms.In this review, we intend to discuss the progress over the last two decades in understanding the alternative colistin mechanisms of action and different strategies used by bacteria to develop resistance against colistin, besides providing an update about what is previously recognized and what is novel concerning colistin resistance.

Microbial Resistance Movements: An Overview of Global Public Health Threats Posed by Antimicrobial Resistance, and How Best to Counter

Antibiotics changed medical practice by significantly decreasing the morbidity and mortality associated with bacterial infection. However, infectious diseases remain the leading cause of death in the world. There is global concern about the rise in antimicrobial resistance (AMR), which affects both developed and developing countries. AMR is a public health challenge with extensive health, economic, and societal implications. This paper sets AMR in context, starting with the history of antibiotics, including the discovery of penicillin and the golden era of antibiotics, before exploring the problems and challenges we now face due to AMR. Among the factors discussed is the low level of development of new antimicrobials and the irrational prescribing of antibiotics in developed and developing countries. A fundamental problem is the knowledge, attitude, and practice (KAP) regarding antibiotics among medical practitioners, and we explore this aspect in some depth, including a discussion on the KAP among medical students. We conclude with suggestions on how to address this public health threat, including recommendations on training medical students about antibiotics, and strategies to overcome the problems of irrational antibiotic prescribing and AMR.

The War against Bad Bugs: Fighting the Resistance

Multidrug-resistant (MDR) microorganisms have become a growing concern, especially in regions with high prevalence [...]

Polymyxin Triple Combinations against Polymyxin-Resistant, Multidrug-Resistant, KPC-Producing Klebsiella pneumoniae

Resistance to polymyxin antibiotics is increasing. Without new antibiotic classes, combination therapy is often required. We systematically investigated bacterial killing with polymyxin-based combinations against multidrug-resistant (including polymyxin-resistant), carbapenemase-producing Klebsiella pneumoniae Monotherapies and double- and triple-combination therapies were compared to identify the most efficacious treatment using static time-kill studies (24 h, six isolates), an in vitro pharmacokinetic/pharmacodynamic model (IVM; 48 h, two isolates), and the mouse thigh infection model (24 h, six isolates). In static time-kill studies, all monotherapies (polymyxin B, rifampin, amikacin, meropenem, or minocycline) were ineffective. Initial bacterial killing was enhanced with various polymyxin B-containing double combinations; however, substantial regrowth occurred in most cases by 24 h. Most polymyxin B-containing triple combinations provided greater and more sustained killing than double combinations. Standard dosage regimens of polymyxin B (2.5 mg/kg of body weight/day), rifampin (600 mg every 12 h), and amikacin (7.5 mg/kg every 12 h) were simulated in the IVM. Against isolate ATH 16, no viable bacteria were detected across 5 to 25 h with triple therapy, with regrowth to ∼2-log10 CFU/ml occurring at 48 h. Against isolate BD 32, rapid initial killing of ∼3.5-log10 CFU/ml at 5 h was followed by a slow decline to ∼2-log10 CFU/ml at 48 h. In infected mice, polymyxin B monotherapy (60 mg/kg/day) generally was ineffective. With triple therapy (polymyxin B at 60 mg/kg/day, rifampin at 120 mg/kg/day, and amikacin at 300 mg/kg/day), at 24 h there was an ∼1.7-log10 CFU/thigh reduction compared to the starting inoculum for all six isolates. Our results demonstrate that the polymyxin B-rifampin-amikacin combination significantly enhanced in vitro and in vivo bacterial killing, providing important information for the optimization of polymyxin-based combinations in patients.

A One Health Comparative Assessment of Antimicrobial Resistance in Generic and Extended-Spectrum Cephalosporin-Resistant Escherichia coli from Beef Production, Sewage and Clinical Settings

This study aimed to compare antimicrobial resistance (AMR) in extended-spectrum cephalosporin-resistant and generic Escherichia coli from a One Health continuum of the beef production system in Alberta, Canada. A total of 705 extended-spectrum cephalosporin-resistant E. coli (ESC^r) were obtained from: cattle feces (CFeces, n = 382), catch basins (CBasins, n = 137), surrounding streams (SStreams, n = 59), beef processing plants (BProcessing, n = 4), municipal sewage (MSewage; n = 98) and human clinical specimens (CHumans, n = 25). Generic isolates (663) included: CFeces (n = 142), CBasins (n = 185), SStreams (n = 81), BProcessing (n = 159) and MSewage (n = 96). All isolates were screened for antimicrobial susceptibility to 9 antimicrobials and two clavulanic acid combinations. In ESC^r, oxytetracycline (87.7%), ampicillin (84.4%) and streptomycin (73.8%) resistance phenotypes were the most common, with source influencing AMR prevalence (p < 0.001). In generic E. coli, oxytetracycline (51.1%), streptomycin (22.6%), ampicillin (22.5%) and sulfisoxazole (14.3%) resistance were most common. Overall, 88.8% of ESC^r, and 26.7% of generic isolates exhibited multi-drug resistance (MDR). MDR in ESC^r was high from all sources: CFeces (97.1%), MSewage (96.9%), CHumans (96%), BProcessing (100%), CBasins (70.5%) and SStreams (61.4%). MDR in generic E. coli was lower with CFeces (45.1%), CBasins (34.6%), SStreams (23.5%), MSewage (13.6%) and BProcessing (10.7%). ESBL phenotypes were confirmed in 24.7% (n = 174) ESC^r and 0.6% of generic E. coli. Prevalence of bla genes in ESC^r were bla_CTXM (30.1%), bla_CTXM-1 (21.6%), bla_TEM (20%), bla_CTXM-9 (7.9%), bla_OXA (3.0%), bla_CTXM-2 (6.4%), bla_SHV (1.4%) and AmpC β-lactamase bla_CMY (81.3%). The lower AMR in ESC^r from SStreams and BProcessing and higher AMR in CHumans and CFeces likely reflects antimicrobial use in these environments. Although MDR levels were higher in ESC^r as compared to generic E. coli, AMR to the same antimicrobials ranked high in both ESC^r and generic E. coli sub-populations. This suggests that both sub-populations reflect similar AMR trends and are equally useful for AMR surveillance. Considering that MDR ESC^r MSewage isolates were obtained without enrichment, while those from CFeces were obtained with enrichment, MSewage may serve as a hot spot for MDR emergence and dissemination.

Multi-Drug-Resistant Organisms in Burn Infections

Background: Infection is the most frequent complication after severe burns and remains the predominant cause of death. Burn patients may require multiple courses of antibiotics, lengthy hospitalizations, and invasive procedures that place burn patients at especially high risk for infections with multi-drug-resistant organisms (MDROs). Methods: The published literature on MDROs in burn patients was reviewed to develop a strategy for managing these infections. Results: Within a burn unit meticulous infection prevention and control measures and effective antimicrobial stewardship can limit MDRO propagation and decrease the antibiotic pressure driving the selection of MDROs from less resistant strains. Several new antimicrobial agents have been developed offering potential therapeutic options, but familiarity with their benefits and limitations is required for safe utilization. Successful management of MDRO burn infections is supported by a multifactorial approach. Novel non-antibiotic therapeutics may help combat MDRO infections and outbreaks. Conclusions: Multi-drug-resistant organisms are being identified with increasing frequency in burn patients. Effective sensitivity testing is essential to identify MDROs and to direct appropriate antibiotic choices for patient treatment.

Preventing sepsis development in complicated urinary tract infections

Introduction: Urinary tract infections (UTIs) are the most prevalent infections in the community and the most common reason for antimicrobial prescribing in ambulatory care. A UTI is defined as complicated when urinary tract anatomical abnormalities or urinary devices are present, when it is recurrent and when associated with immunodeficiency. Complicated UTIs (cUTIs) have a higher risk of treatment failure and often require longer antimicrobial treatment courses. cUTIs, especially those which are healthcare-associated, are often due to multidrug resistant organisms (MDROs).Areas covered: This article will review the available evidence in relation to prevention of sepsis in cUTI, evaluating the risk factors associated with sepsis development. Published articles from January 2005 to September 2019 on UTIs and sepsis prevention in complicated UTIs were identified by using MEDLINE (National Library of Medicine Bethesda MD) and by reviewing the references of retrieved articles.Expert opinion: Prevention of sepsis relies on prompt and timely diagnosis of cUTI, early identification of the causative organism, removal of obstructions and source control, proper and adequate empirical/targeted antimicrobial treatment. In particular, source control, i.e. removal of urinary obstructions, infected stents, urinary catheters, nephrostomies, and drainage of hydronephrosis/abscess, is essential for preventing the development and progression of sepsis.

Optimizing therapy in carbapenem-resistant Enterobacteriaceae infections. Curr Opin Infect Dis. 2018;31:566-577. [PMID: 30379732 DOI: 10.1097/qco.0000000000000493]

PURPOSE OF REVIEW

In the absence of randomized clinical trial data, questions remain regarding the optimal treatment of carbapenem-resistant Enterobacteriaceae (CRE) infections. CRE have historically been susceptible to polymyxins, tigecycline or aminoglycosides (mostly gentamicin), and these antibiotics have long been considered the drugs of choice for CRE infections, although varying rates of resistance to all have been reported. This review looks at data from clinical studies assessing the outcomes of CRE infections treated with different antibiotic regimens.

RECENT FINDINGS

The recently approved fixed-dose combination agent, ceftazidime-avibactam (CAZ-AVI), is active against KPC and OXA-48-producing Enterobacteriaceae. The limited clinical data available on CAZ-AVI indicate that it is associated with survival benefits relative to other commonly used regimens, although development of resistance is a concern. New drugs active against CRE isolates (including the recently approved meropenem-vaborbactam) are in different stages of development.

SUMMARY

CAZ-AVI and meropenem-vaborbactam seem destined to become the backbone of target therapy for high-risk patients with severe infections caused by susceptible CRE strains. However, empirical therapy should be based on risk factors to be defined in the near future, whereas the necessity of combinations with CAZ-AVI requires further studies. Polymyxins are still important options for low-risk patients with susceptible CRE infections, but also for high-risk patients in regions where metallo-β-lactamase-producing CRE predominate because CAZ-AVI and meropenem-vaborbactam are both ineffective against these strains.

Emergent Polymyxin Resistance: End of an Era?

Until recently, the polymyxin antibiotics were used sparingly due to dose limiting toxicities. However, the lack of therapeutic alternatives for infections caused by highly resistant Gram-negative bacteria has led to the increased use of the polymyxins. Unfortunately, the world has witnessed increased rates of polymyxin resistance in the last decade, which is likely in part due to its irrational use in human and veterinary medicine. The spread of polymyxin resistance has been aided by the dissemination of the transferable polymyxin-resistance gene, mcr, in humans and the environment. The mortality of colistin-resistant bacteria (CoRB) infections varies in different reports. However, poor clinical outcome was associated with prior colistin treatment, illness severity, complications, and multidrug resistance. Detection of polymyxin resistance in the clinic is possible through multiple robust and practical tests, including broth microdilution susceptibility testing, chromogenic agar testing, and molecular biology assays. There are multiple risk factors that increase a person’s risk for infection with a polymyxin-resistant bacteria, including age, prior colistin treatment, hospitalization, and ventilator support. For patients that are determined to be infected by polymyxin-resistant bacteria, various antibiotic treatment options currently exist. The rising trend of polymyxin resistance threatens patient care and warrants effective control.

Comparative Epidemiology and Resistance Trends of Common Urinary Pathogens in a Tertiary-Care Hospital: A 10-Year Surveillance Study

Background and Objective: Urinary tract infections (UTIs) are common in human medicine, affecting large patient populations worldwide. The principal cause of UTIs is uropathogenic Escherichia coli (UPEC) and Klebsiella, both in community and nosocomial settings. The assessment of local data on prevalence and resistance is essential to evaluate trends over time and to reflect on the national situation, compared to international data, using the methods of analytical epidemiology. Materials and Methods: The aim of this study was to assess resistance trends and epidemiology of UTIs caused by E. coli and Klebsiella species in inpatients and outpatients at a tertiary-care hospital in Hungary, using microbiological data. To evaluate resistance trends, several antibiotics were chosen as indicator drugs, based on local utilization data. Results: E. coli was the most prevalent isolate, representing 56.75 ± 4.86% for outpatients and 42.29 ± 2.94% for inpatients. For E. coli, the ratio of resistant strains for several antibiotics was significantly higher in the inpatient group, while in Klebsiella, similar trends were only observed for gentamicin. Extended-spectrum β-lactamase (ESBL)-producing isolates were detected in 4.33-9.15% and 23.22-34.22% from outpatient, 8.85-38.97% and 10.89-36.06% from inpatient samples for E. coli and Klebsiella, respectively. Conclusions: Resistance developments in common UTI pathogens (especially to fosfomycin, sulfamethoxazole-trimethoprim, fluoroquinolones, and 3rd generation cephalosporins), seriously curb therapeutic options, especially in outpatient settings.

Treatment Options for Colistin Resistant Klebsiella pneumoniae: Present and Future

Multidrug-resistant (MDR) Klebsiella pneumoniae represents an increasing threat to human health, causing difficult-to-treat infections with a high mortality rate. Since colistin is one of the few treatment options for carbapenem-resistant K. pneumoniae infections, colistin resistance represents a challenge due to the limited range of potentially available effective antimicrobials, including tigecycline, gentamicin, fosfomycin and ceftazidime/avibactam. Moreover, the choice of these antimicrobials depends on their pharmacokinetics/pharmacodynamics properties, the site of infection and the susceptibility profile of the isolated strain, and is sometimes hampered by side effects. This review describes the features of colistin resistance in K. pneumoniae and the characteristics of the currently available antimicrobials for colistin-resistant MDR K. pneumoniae, as well as the characteristics of novel antimicrobial options, such as the soon-to-be commercially available plazomicin and cefiderocol. Finally, we consider the future use of innovative therapeutic strategies in development, including bacteriophages therapy and monoclonal antibodies.

Genomic characterization of a KPC-23-producing Klebsiella pneumoniae ST258 clinical isolate resistant to ceftazidime-avibactam

OBJECTIVES

We characterized the first ceftazidime-avibactam-resistant KPC-producing-Klebsiella pneumoniae clinical isolate detected in Greece, before the introduction of ceftazidime-avibactam in clinical practice.

METHODS

K. pneumoniae KP-90 was isolated from a hospitalized patient in Thessaloniki during a nationwide surveillance study conducted between 2014 and 2016. Antimicrobial susceptibility was tested against a panel of agents. Whole-genome sequencing (Ion Torrent TM platform) of the isolate was carried out to identify the acquired resistance genes and mutations that were associated with ceftazidime-avibactam resistance.

RESULTS

The K. pneumoniae isolate belonged to multilocus sequence type ST258 and harboured bla_KPC-23 as the only carbapenemase gene. The isolate had a minimum inhibitory concentration (MIC) of 16 mg/L to ceftazidime-avibactam and was highly resistant to imipenem, meropenem (MICs, 512 mg/L) and ceftazidime (MIC, >1024 mg/L). bla_KPC-23 was detected on a Tn4401a transposon, located on a pKPQIL-type plasmid. A non-functional outer membrane protein OmpK35 and an OmpK36 variant that had been previously associated with K. pneumoniae isolates of ST258 were detected. Transformation studies with Escherichia coli TOP10 showed that KPC-23 offered similar carbapenem MICs as KPC-2 and KPC-3. However, KPC-23 conferred a four-fold higher ceftazidime MIC (>1024 mg/L), which in the presence of avibactam was reduced (>7-fold) to 8 mg/L, which is just within the limit of the susceptibility breakpoint.

CONCLUSIONS

Ceftazidime-avibactam resistance in a KPC-23- producing K. pneumoniae clinical isolate was due to increased ceftazidime hydrolysis and was likely enhanced by OmpK35 porin deficiency.