# | Rank | Similarity | Title + Abs. | Year | PMID |
|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | 4 | 5 |
| 9777 | 0 | 1.0000 | Colistin resistance in Acinetobacter baumannii is mediated by complete loss of lipopolysaccharide production. Infections caused by multidrug-resistant (MDR) Gram-negative bacteria represent a major global health problem. Polymyxin antibiotics such as colistin have resurfaced as effective last-resort antimicrobials for use against MDR Gram-negative pathogens, including Acinetobacter baumannii. Here we show that A. baumannii can rapidly develop resistance to polymyxin antibiotics by complete loss of the initial binding target, the lipid A component of lipopolysaccharide (LPS), which has long been considered to be essential for the viability of Gram-negative bacteria. We characterized 13 independent colistin-resistant derivatives of A. baumannii type strain ATCC 19606 and showed that all contained mutations within one of the first three genes of the lipid A biosynthesis pathway: lpxA, lpxC, and lpxD. All of these mutations resulted in the complete loss of LPS production. Furthermore, we showed that loss of LPS occurs in a colistin-resistant clinical isolate of A. baumannii. This is the first report of a spontaneously occurring, lipopolysaccharide-deficient, Gram-negative bacterium. | 2010 | 20855724 |
| 9779 | 1 | 0.9998 | Mechanisms of Polymyxin Resistance. Polymyxin antibiotics are increasingly being used as last-line therapeutic options against a number of multidrug resistant bacteria. These antibiotics show strong bactericidal activity against a range of Gram-negative bacteria, but with the increased use of these antibiotics resistant strains are emerging at an alarming rate. Furthermore, some Gram-negative species, such as Neisseria meningitidis, Proteus mirabilis and Burkholderia spp., are intrinsically resistant to the action of polymyxins. Most identified polymyxin resistance mechanisms in Gram-negative bacteria involve changes to the lipopolysaccharide (LPS) structure, as polymyxins initially interact with the negatively charged lipid A component of LPS. The controlled addition of positively charged residues such as 4-amino-(L)-arabinose, phosphoethanolamine and/or galactosamine to LPS results in a reduced negative charge on the bacterial surface and therefore reduced interaction between the polymyxin and the LPS. Polymyxin resistant species produce LPS that intrinsically contains one or more of these additions. While the genes necessary for most of these additions are chromosomally encoded, plasmid-borne phosphoethanolamine transferases (mcr-1 to mcr-8) have recently been identified and these plasmids threaten to increase the rate of dissemination of clinically relevant colistin resistance. Uniquely, Acinetobacter baumannii can also become highly resistant to polymyxins via spontaneous mutations in the lipid A biosynthesis genes lpxA, lpxC or lpxD such that they produce no LPS or lipid A. A range of other non-LPS-dependent polymyxin resistance mechanisms has also been identified in bacteria, but these generally result in only low levels of resistance. These include increased anionic capsular polysaccharide production in Klebsiella pneumoniae, expression of efflux systems such as MtrCDE in N. meningitidis, and altered expression of outer membrane proteins in a small number of species. | 2019 | 31364071 |
| 9778 | 2 | 0.9998 | Antibiotic class with potent in vivo activity targeting lipopolysaccharide synthesis in Gram-negative bacteria. Here, we describe the identification of an antibiotic class acting via LpxH, a clinically unexploited target in lipopolysaccharide synthesis. The lipopolysaccharide synthesis pathway is essential in most Gram-negative bacteria and there is no analogous pathway in humans. Based on a series of phenotypic screens, we identified a hit targeting this pathway that had activity on efflux-defective strains of Escherichia coli. We recognized common structural elements between this hit and a previously published inhibitor, also with activity against efflux-deficient bacteria. With the help of X-ray structures, this information was used to design inhibitors with activity on efflux-proficient, wild-type strains. Optimization of properties such as solubility, metabolic stability and serum protein binding resulted in compounds having potent in vivo efficacy against bloodstream infections caused by the critical Gram-negative pathogens E. coli and Klebsiella pneumoniae. Other favorable properties of the series include a lack of pre-existing resistance in clinical isolates, and no loss of activity against strains expressing extended-spectrum-β-lactamase, metallo-β-lactamase, or carbapenemase-resistance genes. Further development of this class of antibiotics could make an important contribution to the ongoing struggle against antibiotic resistance. | 2024 | 38579010 |
| 9780 | 3 | 0.9998 | Colistin resistance in Escherichia coli confers protection of the cytoplasmic but not outer membrane from the polymyxin antibiotic. Colistin is a polymyxin antibiotic of last resort for the treatment of infections caused by multi-drug-resistant Gram-negative bacteria. By targeting lipopolysaccharide (LPS), the antibiotic disrupts both the outer and cytoplasmic membranes, leading to bacterial death and lysis. Colistin resistance in Escherichia coli occurs via mutations in the chromosome or the acquisition of mobilized colistin-resistance (mcr) genes. Both these colistin-resistance mechanisms result in chemical modifications to the LPS, with positively charged moieties added at the cytoplasmic membrane before the LPS is transported to the outer membrane. We have previously shown that MCR-1-mediated LPS modification protects the cytoplasmic but not the outer membrane from damage caused by colistin, enabling bacterial survival. However, it remains unclear whether this observation extends to colistin resistance conferred by other mcr genes, or resistance due to chromosomal mutations. Using a panel of clinical E. coli that had acquired mcr -1, -1.5, -2, -3, -3.2 or -5, or had acquired polymyxin resistance independently of mcr genes, we found that almost all isolates were susceptible to colistin-mediated permeabilization of the outer, but not cytoplasmic, membrane. Furthermore, we showed that permeabilization of the outer membrane of colistin-resistant isolates by the polymyxin is in turn sufficient to sensitize bacteria to the antibiotic rifampicin, which normally cannot cross the LPS monolayer. These findings demonstrate that colistin resistance in these E. coli isolates is due to protection of the cytoplasmic but not outer membrane from colistin-mediated damage, regardless of the mechanism of resistance. | 2021 | 34723787 |
| 5060 | 4 | 0.9998 | Nonclonal Emergence of Colistin Resistance Associated with Mutations in the BasRS Two-Component System in Escherichia coli Bloodstream Isolates. Infections by multidrug-resistant Gram-negative bacteria are increasingly common, prompting the renewed interest in the use of colistin. Colistin specifically targets Gram-negative bacteria by interacting with the anionic lipid A moieties of lipopolysaccharides, leading to membrane destabilization and cell death. Here, we aimed to uncover the mechanisms of colistin resistance in nine colistin-resistant Escherichia coli strains and one Escherichia albertii strain. These were the only colistin-resistant strains of 1,140 bloodstream Escherichia isolates collected in a tertiary hospital over a 10-year period (2006 to 2015). Core-genome phylogenetic analysis showed that each patient was colonized by a unique strain, suggesting that colistin resistance was acquired independently in each strain. All colistin-resistant strains had lipid A that was modified with phosphoethanolamine. In addition, two E. coli strains had hepta-acylated lipid A species, containing an additional palmitate compared to the canonical hexa-acylated E. coli lipid A. One E. coli strain carried the mobile colistin resistance (mcr) gene mcr-1.1 on an IncX4-type plasmid. Through construction of chromosomal transgene integration mutants, we experimentally determined that mutations in basRS, encoding a two-component signal transduction system, contributed to colistin resistance in four strains. We confirmed these observations by reversing the mutations in basRS to the sequences found in reference strains, resulting in loss of colistin resistance. While the mcr genes have become a widely studied mechanism of colistin resistance in E. coli, sequence variation in basRS is another, potentially more prevalent but relatively underexplored, cause of colistin resistance in this important nosocomial pathogen.IMPORTANCE Multidrug resistance among Gram-negative bacteria has led to the use of colistin as a last-resort drug. The cationic colistin kills Gram-negative bacteria through electrostatic interaction with the anionic lipid A moiety of lipopolysaccharides. Due to increased use in clinical and agricultural settings, colistin resistance has recently started to emerge. In this study, we used a combination of whole-genome sequence analysis and experimental validation to characterize the mechanisms through which Escherichia coli strains from bloodstream infections can develop colistin resistance. We found no evidence of direct transfer of colistin-resistant isolates between patients. The lipid A of all isolates was modified by the addition of phosphoethanolamine. In four isolates, colistin resistance was experimentally verified to be caused by mutations in the basRS genes, encoding a two-component regulatory system. Our data show that chromosomal mutations are an important cause of colistin resistance among clinical E. coli isolates. | 2020 | 32161146 |
| 4827 | 5 | 0.9998 | A multidrug resistance plasmid contains the molecular switch for type VI secretion in Acinetobacter baumannii. Infections with Acinetobacter baumannii, one of the most troublesome and least studied multidrug-resistant superbugs, are increasing at alarming rates. A. baumannii encodes a type VI secretion system (T6SS), an antibacterial apparatus of Gram-negative bacteria used to kill competitors. Expression of the T6SS varies among different strains of A. baumannii, for which the regulatory mechanisms are unknown. Here, we show that several multidrug-resistant strains of A. baumannii harbor a large, self-transmissible resistance plasmid that carries the negative regulators for T6SS. T6SS activity is silenced in plasmid-containing, antibiotic-resistant cells, while part of the population undergoes frequent plasmid loss and activation of the T6SS. This activation results in T6SS-mediated killing of competing bacteria but renders A. baumannii susceptible to antibiotics. Our data show that a plasmid that has evolved to harbor antibiotic resistance genes plays a role in the differentiation of cells specialized in the elimination of competing bacteria. | 2015 | 26170289 |
| 9776 | 6 | 0.9997 | Mechanisms of polymyxin resistance: acquired and intrinsic resistance in bacteria. Polymyxins are polycationic antimicrobial peptides that are currently the last-resort antibiotics for the treatment of multidrug-resistant, Gram-negative bacterial infections. The reintroduction of polymyxins for antimicrobial therapy has been followed by an increase in reports of resistance among Gram-negative bacteria. Some bacteria, such as Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii, develop resistance to polymyxins in a process referred to as acquired resistance, whereas other bacteria, such as Proteus spp., Serratia spp., and Burkholderia spp., are naturally resistant to these drugs. Reports of polymyxin resistance in clinical isolates have recently increased, including acquired and intrinsically resistant pathogens. This increase is considered a serious issue, prompting concern due to the low number of currently available effective antibiotics. This review summarizes current knowledge concerning the different strategies bacteria employ to resist the activities of polymyxins. Gram-negative bacteria employ several strategies to protect themselves from polymyxin antibiotics (polymyxin B and colistin), including a variety of lipopolysaccharide (LPS) modifications, such as modifications of lipid A with phosphoethanolamine and 4-amino-4-deoxy-L-arabinose, in addition to the use of efflux pumps, the formation of capsules and overexpression of the outer membrane protein OprH, which are all effectively regulated at the molecular level. The increased understanding of these mechanisms is extremely vital and timely to facilitate studies of antimicrobial peptides and find new potential drugs targeting clinically relevant Gram-negative bacteria. | 2014 | 25505462 |
| 4824 | 7 | 0.9997 | Chemogenomic Screen for Imipenem Resistance in Gram-Negative Bacteria. Carbapenem-resistant Gram-negative bacteria are considered a major threat to global health. Imipenem (IMP) is used as a last line of treatment against these pathogens, but its efficacy is diminished by the emergence of resistance. We applied a whole-genome screen in Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa isolates that were submitted to chemical mutagenesis, selected for IMP resistance, and characterized by next-generation sequencing. A comparative analysis of IMP-resistant clones showed that most of the highly mutated genes shared by the three species encoded proteins involved in transcription or signal transduction. Of these, the rpoD gene was one of the most prevalent and an E. coli strain disrupted for rpoD displayed a 4-fold increase in resistance to IMP. E. coli and K. pneumoniae also specifically shared several mutated genes, most involved in membrane/cell envelope biogenesis, and the contribution in IMP susceptibility was experimentally proven for amidases, transferases, and transglycosidases. P. aeruginosa differed from the two Enterobacteriaceae isolates with two different resistance mechanisms, with one involving mutations in the oprD porin or, alternatively, in two-component systems. Our chemogenomic screen performed with the three species has highlighted shared and species-specific responses to IMP.IMPORTANCE Gram-negative carbapenem-resistant bacteria are a major threat to global health. The use of genome-wide screening approaches to probe for genes or mutations enabling resistance can lead to identification of molecular markers for diagnostics applications. We describe an approach called Mut-Seq that couples chemical mutagenesis and next-generation sequencing for studying resistance to imipenem in the Gram-negative bacteria Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa The use of this approach highlighted shared and species-specific responses, and the role in resistance of a number of genes involved in membrane biogenesis, transcription, and signal transduction was functionally validated. Interestingly, some of the genes identified were previously considered promising therapeutic targets. Our genome-wide screen has the potential to be extended outside drug resistance studies and expanded to other organisms. | 2019 | 31744905 |
| 6274 | 8 | 0.9997 | Transcriptomics Reveals How Minocycline-Colistin Synergy Overcomes Antibiotic Resistance in Multidrug-Resistant Klebsiella pneumoniae. Multidrug-resistant Gram-negative bacteria are a rapidly growing public health threat, and the development of novel antimicrobials has failed to keep pace with their emergence. Synergistic combinations of individually ineffective drugs present a potential solution, yet little is understood about the mechanisms of most such combinations. Here, we show that the combination of colistin (polymyxin E) and minocycline has a high rate of synergy against colistin-resistant and minocycline-intermediate or -resistant strains of Klebsiella pneumoniae. Furthermore, using transcriptome sequencing (RNA-Seq), we characterized the transcriptional profiles of these strains when treated with the drugs individually and in combination. We found a striking similarity between the transcriptional profiles of bacteria treated with the combination of colistin and minocycline at individually subinhibitory concentrations and those of the same isolates treated with minocycline alone. We observed a similar pattern with the combination of polymyxin B nonapeptide (a polymyxin B analogue that lacks intrinsic antimicrobial activity) and minocycline. We also found that genes involved in polymyxin resistance and peptidoglycan biosynthesis showed significant differential gene expression in the different treatment conditions, suggesting possible mechanisms for the antibacterial activity observed in the combination. These findings suggest that the synergistic activity of this combination against bacteria resistant to each drug alone involves sublethal outer membrane disruption by colistin, which permits increased intracellular accumulation of minocycline. | 2022 | 35041511 |
| 9774 | 9 | 0.9997 | A naturally inspired antibiotic to target multidrug-resistant pathogens. Gram-negative bacteria are responsible for an increasing number of deaths caused by antibiotic-resistant infections(1,2). The bacterial natural product colistin is considered the last line of defence against a number of Gram-negative pathogens. The recent global spread of the plasmid-borne mobilized colistin-resistance gene mcr-1 (phosphoethanolamine transferase) threatens the usefulness of colistin(3). Bacteria-derived antibiotics often appear in nature as collections of similar structures that are encoded by evolutionarily related biosynthetic gene clusters. This structural diversity is, at least in part, expected to be a response to the development of natural resistance, which often mechanistically mimics clinical resistance. Here we propose that a solution to mcr-1-mediated resistance might have evolved among naturally occurring colistin congeners. Bioinformatic analysis of sequenced bacterial genomes identified a biosynthetic gene cluster that was predicted to encode a structurally divergent colistin congener. Chemical synthesis of this structure produced macolacin, which is active against Gram-negative pathogens expressing mcr-1 and intrinsically resistant pathogens with chromosomally encoded phosphoethanolamine transferase genes. These Gram-negative bacteria include extensively drug-resistant Acinetobacter baumannii and intrinsically colistin-resistant Neisseria gonorrhoeae, which, owing to a lack of effective treatment options, are considered among the highest level threat pathogens(4). In a mouse neutropenic infection model, a biphenyl analogue of macolacin proved to be effective against extensively drug-resistant A. baumannii with colistin-resistance, thus providing a naturally inspired and easily produced therapeutic lead for overcoming colistin-resistant pathogens. | 2022 | 34987225 |
| 4822 | 10 | 0.9997 | A Molecular Perspective on Colistin and Klebsiella pneumoniae: Mode of Action, Resistance Genetics, and Phenotypic Susceptibility. Klebsiella pneumoniae is a rod-shaped, encapsulated, Gram-negative bacteria associated with multiple nosocomial infections. Multidrug-resistant (MDR) K. pneumoniae strains have been increasing and the therapeutic options are increasingly limited. Colistin is a long-used, polycationic, heptapeptide that has regained attention due to its activity against Gram-negative bacteria, including the MDR K. pneumoniae strains. However, this antibiotic has a complex mode of action that is still under research along with numerous side-effects. The acquisition of colistin resistance is mainly associated with alteration of lipid A net charge through the addition of cationic groups synthesized by the gene products of a multi-genic regulatory network. Besides mutations in these chromosomal genes, colistin resistance can also be achieved through the acquisition of plasmid-encoded genes. Nevertheless, the diversity of molecular markers for colistin resistance along with some adverse colistin properties compromises the reliability of colistin-resistance monitorization methods. The present review is focused on the colistin action and molecular resistance mechanisms, along with specific limitations on drug susceptibility testing for K. pneumoniae. | 2021 | 34202395 |
| 9773 | 11 | 0.9997 | Cross resistance emergence to polymyxins in Acinetobacter baumannii exposed in vitro to an antimicrobial peptide. Multidrug-resistant bacteria are a growing public health concern. Antimicrobial peptides (AMPs) are proposed alternatives to classical antibiotics towards infections caused by resistant bacteria. TAT-RasGAP(317-326) is an AMP able to target Gram-negative bacteria and is especially efficient towards Acinetobacter baumannii. In this study, we performed in vitro resistance selection on several A. baumannii strains, in order to determine to which extent these bacteria can develop resistance to TAT-RasGAP(317-326). A. baumannii rapidly developed resistance to TAT-RasGAP(317-326) and subsequently, in approximately half of the cases, cross-resistance to last-resort polypeptidic antibiotics polymyxins. Cross-resistant isolates predominantly bore mutations in the pmrAB operon, involved in modulation of lipopolysaccharides' charge at the bacterial surface, similarly to polymyxin-resistant clinical isolates. We thus show here that contact of A. baumannii with an AMP structurally different from polymyxins can induce unexpected cross-resistance towards them. This indicates that precautions must be taken for the clinical application of AMPs. | 2025 | 40442488 |
| 4823 | 12 | 0.9997 | A Review of Resistance to Polymyxins and Evolving Mobile Colistin Resistance Gene (mcr) among Pathogens of Clinical Significance. The global rise in antibiotic resistance in bacteria poses a major challenge in treating infectious diseases. Polymyxins (e.g., polymyxin B and colistin) are last-resort antibiotics against resistant Gram-negative bacteria, but the effectiveness of polymyxins is decreasing due to widespread resistance among clinical isolates. The aim of this literature review was to decipher the evolving mechanisms of resistance to polymyxins among pathogens of clinical significance. We deciphered the molecular determinants of polymyxin resistance, including distinct intrinsic molecular pathways of resistance as well as evolutionary characteristics of mobile colistin resistance. Among clinical isolates, Acinetobacter stains represent a diversified evolution of resistance, with distinct molecular mechanisms of intrinsic resistance including naxD, lpxACD, and stkR gene deletion. On the other hand, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa are usually resistant via the PhoP-PhoQ and PmrA-PmrB pathways. Molecular evolutionary analysis of mcr genes was undertaken to show relative relatedness across the ten main lineages. Understanding the molecular determinants of resistance to polymyxins may help develop suitable and effective methods for detecting polymyxin resistance determinants and the development of novel antimicrobial molecules. | 2023 | 37998799 |
| 9775 | 13 | 0.9997 | 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. | 2021 | 34476235 |
| 4825 | 14 | 0.9997 | Proof of the triple prerequisite conditions which are essential for carbapenem resistance development in Klebsiella pneumoniae by using radiation-mediated mutagenesis. Evolution of multi-drug resistant bacteria has led to worldwide research to better understand the various resistance mechanisms in these strains. Every year, novel information on carbapenem resistance and its mechanisms is being discovered. In this study, radiation-mediated mutagenesis was used to transform a carbapenem-resistant Klebsiella pneumoniae strain to a carbapenem-susceptible bacterium. Through this process, we proved three conditions of loss of the OmpK35 and the OmpK36 genes and acquisition of blaCMY-10 worked together to produce carbapenem resistance in K. pneumoniae. Loss of only one of the porins did not evoke carbapenem resistance. This is the first report on the essential contribution of these three components of carbapenem resistance in K. pneumoniae. | 2021 | 33469646 |
| 2502 | 15 | 0.9997 | Rapid detection of colistin resistance in Acinetobacter baumannii using MALDI-TOF-based lipidomics on intact bacteria. With the dissemination of extremely drug resistant bacteria, colistin is now considered as the last-resort therapy for the treatment of infection caused by Gram-negative bacilli (including carbapenemase producers). Unfortunately, the increase use of colistin has resulted in the emergence of resistance as well. In A. baumannii, colistin resistance is mostly caused by the addition of phosphoethanolamine to the lipid A through the action of a phosphoethanolamine transferase chromosomally-encoded by the pmrC gene, which is regulated by the two-component system PmrA/PmrB. In A. baumannii clinical isolate the main resistance mechanism to colistin involves mutations in pmrA, pmrB or pmrC genes leading to the overexpression of pmrC. Although, rapid detection of resistance is one of the key issues to improve the treatment of infected patient, detection of colistin resistance in A. baumannii still relies on MIC determination through microdilution, which is time-consuming (16-24 h). Here, we evaluated the performance of a recently described MALDI-TOF-based assay, the MALDIxin test, which allows the rapid detection of colistin resistance-related modifications to lipid A (i.e phosphoethanolamine addition). This test accurately detected all colistin-resistant A. baumannii isolates in less than 15 minutes, directly on intact bacteria with a very limited sample preparation prior MALDI-TOF analysis. | 2018 | 30442963 |
| 6275 | 16 | 0.9997 | Resistance to fosfomycin: Mechanisms, Frequency and Clinical Consequences. Fosfomycin has been used for the treatment of infections due to susceptible and multidrug-resistant (MDR) bacteria. It inhibits bacterial cell wall synthesis through a unique mechanism of action at a step prior to that inhibited by β-lactams. Fosfomycin enters the bacterium through membrane channels/transporters and inhibits MurA, which initiates peptidoglycan (PG) biosynthesis of the bacterial cell wall. Several bacteria display inherent resistance to fosfomycin mainly through MurA mutations. Acquired resistance involves, in order of decreasing frequency, modifications of membrane transporters that prevent fosfomycin from entering the bacterial cell, acquisition of plasmid-encoded genes that inactivate fosfomycin, and MurA mutations. Fosfomycin resistance develops readily in vitro but less so in vivo. Mutation frequency is higher among Pseudomonas aeruginosa and Klebsiella spp. compared with Escherichia coli and is associated with fosfomycin concentration. Mutations in cAMP regulators, fosfomycin transporters and MurA seem to be associated with higher biological cost in Enterobacteriaceae but not in Pseudomonas spp. The contribution of fosfomycin inactivating enzymes in emergence and spread of fosfomycin resistance currently seems low-to-moderate, but their presence in transferable plasmids may potentially provide the best means for the spread of fosfomycin resistance in the future. Their co-existence with genes conferring resistance to other antibiotic classes may increase the emergence of MDR strains. Although susceptibility rates vary, rates seem to increase in settings with higher fosfomycin use and among multidrug-resistant pathogens. | 2019 | 30268576 |
| 5056 | 17 | 0.9997 | Step-Wise Increase in Tigecycline Resistance in Klebsiella pneumoniae Associated with Mutations in ramR, lon and rpsJ. Klebsiella pneumoniae is a gram-negative bacterium that causes numerous diseases, including pneumonia and urinary tract infections. An increase in multidrug resistance has complicated the treatment of these bacterial infections, and although tigecycline shows activity against a broad spectrum of bacteria, resistant strains have emerged. In this study, the whole genomes of two clinical and six laboratory-evolved strains were sequenced to identify putative mutations related to tigecycline resistance. Of seven tigecycline-resistant strains, seven (100%) had ramR mutations, five (71.4%) had lon mutations, one (14.2%) had a ramA mutation, and one (14.2%) had an rpsJ mutation. A higher fitness cost was observed in the laboratory-evolved strains but not in the clinical strains. A transcriptome analysis demonstrated high expression of the ramR operon and acrA in all tigecycline-resistant strains. Genes involved in nitrogen metabolism were induced in the laboratory-evolved strains compared with the wild-type and clinical strains, and this difference in nitrogen metabolism reflected the variation between the laboratory-evolved and the clinical strains. Complementation experiments showed that both the wild-type ramR and the lon genes could partially restore the tigecycline sensitivity of K. pneumoniae. We believe that this manuscript describes the first construct of a lon mutant in K. pneumoniae, which allowed confirmation of its association with tigecycline resistance. Our findings illustrate the importance of the ramR operon and the lon and rpsJ genes in K. pneumoniae resistance to tigecycline. | 2016 | 27764207 |
| 5059 | 18 | 0.9997 | Site-selective modifications by lipid A phosphoethanolamine transferases linked to colistin resistance and bacterial fitness. Genes encoding lipid A modifying phosphoethanolamine transferases (PETs) are genetically diverse and can confer resistance to colistin and antimicrobial peptides. To better understand the functional diversity of PETs, we characterized three canonical mobile colistin resistance (mcr) alleles (mcr-1, -3, -9), one intrinsic pet (eptA), and two mcr-like genes (petB, petC) in Escherichia coli. Using an isogenic expression system, we show that mcr-1 and mcr-3 confer similar phenotypes of decreased colistin susceptibility with low fitness costs. mcr-9, which is phylogenetically closely related to mcr-3, and eptA only provide fitness advantages in the presence of sub-inhibitory concentrations of colistin and significantly reduce fitness in media without colistin. PET-B and PET-C were phenotypically distinct from bonafide PETs; neither impacted colistin susceptibility nor caused considerable fitness cost. Strikingly, we found for the first time that different PETs selectively modify different phosphates of lipid A; MCR-1, MCR-3, and PET-C selectively modify the 4'-phosphate, whereas MCR-9 and EptA modify the 1-phosphate. However, 4'-phosphate modifications facilitated by MCR-1 and -3 are associated with lowered colistin susceptibility and low toxicity. Our results suggest that PETs have a wide phenotypic diversity and that increased colistin resistance is associated with specific lipid A modification patterns that have been largely unexplored thus far. IMPORTANCE: Rising levels of resistance to increasing numbers of antimicrobials have led to the revival of last resort antibiotic colistin. Unfortunately, resistance to colistin is also spreading in the form of mcr genes, making it essential to (i) improve the identification of resistant bacteria to allow clinicians to prescribe effective drug regimens and (ii) develop new combination therapies effective at targeting resistant bacteria. Our results demonstrate that PETs, including MCR variants, are site-selective in Escherichia coli and that site-selectivity correlates with the level of susceptibility and fitness costs conferred by certain PETs. Site selectivity associated with a given PET may not only help predict colistin resistance phenotypes but may also provide an avenue to (i) improve drug regimens and (ii) develop new combination therapies to better combat colistin-resistant bacteria. | 2024 | 39611852 |
| 5837 | 19 | 0.9997 | The secondary resistome of multidrug-resistant Klebsiella pneumoniae. Klebsiella pneumoniae causes severe lung and bloodstream infections that are difficult to treat due to multidrug resistance. We hypothesized that antimicrobial resistance can be reversed by targeting chromosomal non-essential genes that are not responsible for acquired resistance but essential for resistant bacteria under therapeutic concentrations of antimicrobials. Conditional essentiality of individual genes to antimicrobial resistance was evaluated in an epidemic multidrug-resistant clone of K. pneumoniae (ST258). We constructed a high-density transposon mutant library of >430,000 unique Tn5 insertions and measured mutant depletion upon exposure to three clinically relevant antimicrobials (colistin, imipenem or ciprofloxacin) by Transposon Directed Insertion-site Sequencing (TraDIS). Using this high-throughput approach, we defined three sets of chromosomal non-essential genes essential for growth during exposure to colistin (n = 35), imipenem (n = 1) or ciprofloxacin (n = 1) in addition to known resistance determinants, collectively termed the "secondary resistome". As proof of principle, we demonstrated that inactivation of a non-essential gene not previously found linked to colistin resistance (dedA) restored colistin susceptibility by reducing the minimum inhibitory concentration from 8 to 0.5 μg/ml, 4-fold below the susceptibility breakpoint (S ≤ 2 μg/ml). This finding suggests that the secondary resistome is a potential target for developing antimicrobial "helper" drugs that restore the efficacy of existing antimicrobials. | 2017 | 28198411 |