Septal Class A Penicillin-Binding Protein Activity and ld -Transpeptidases Mediate Selection of Colistin-Resistant Lipooligosaccharide-Deficient Acinetobacter baumannii (original) (raw)
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The Gram-negative bacterial outer membrane fortifies the cell against environmental toxins including antibiotics. Unique glyco-lipids called lipopolysaccharide/lipooligosaccharide (LPS/LOS) are enriched in the cell-surface monolayer of the outer membrane and promote antimicrobial resistance. Colistin, which targets the lipid A domain of LPS/LOS to lyse the cell, is the last-line treatment for multidrug-resistant Gram-negative infections. Lipid A is essential for the survival of most Gram-negative bacteria, but colistin-resistant Acinetobacter baumannii lacking lipid A were isolated after colistin exposure. Previously, strain ATCC 19606 was the only A. baumannii strain demonstrated to subsist without lipid A. Here, we show that other A. baumannii strains can also survive without lipid A, but some cannot, affording a unique model to study endotoxin essen-tiality. We assessed the capacity of 15 clinical A. baumannii isolates including 9 recent clinical isolates to develop colistin resistance through inactivation of the lipid A biosynthetic pathway, the products of which assemble the LOS precursor. Our investigation determined that expression of the well-conserved penicillin-binding protein (PBP) 1A, prevented LOS-deficient colony isolation. The gly-cosyltransferase activity of PBP1A, which aids in the polymerization of the peptidoglycan cell wall, was lethal to LOS-deficient A. bau-mannii. Global transcriptomic analysis of a PBP1A-deficient mutant and four LOS-deficient A. baumannii strains showed a concomitant increase in transcription of lipoproteins and their transporters. Examination of the LOS-deficient A. baumannii cell surface demonstrated that specific lipoproteins were overexpressed and decorated the cell surface, potentially compensating for LOS removal. This work expands our knowledge of lipid A essentiality and elucidates a drug resistance mechanism. Acinetobacter | peptidoglycan | colistin | lipoprotein | lipopolysaccharide
Antimicrobial Agents and Chemotherapy, 2010
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.
Colistin requires de novo lipopolysaccharide biosynthesis for activity
Colistin is a last resort antibiotic for infections caused by highly drug-resistant Gram-negative pathogens such as Pseudomonas aeruginosa. Unfortunately, treatment failure is common despite low rates of resistance, and efforts to address this are compromised by our poor understanding of colistins mode of action. Here, we show that colistin causes dose-dependent membrane disruption and killing of P. aeruginosa via a process that requires de novo lipopolysaccharide (LPS) biosynthesis. Colistin binds to LPS in the outer membrane (OM), leading to disruption of the cation-bridges that stabilise the lipopolysaccharide molecules. Due to the weakening of these bridges, de novo synthesis of LPS results in the release of lipopolysaccharide from the OM. The subsequent loss of membrane integrity enables colistin to access the cytoplasmic membrane (CM), leading to permeabilisation and bacterial lysis. Inhibition of LPS biosynthesis in Escherichia coli and Klebsiella pneumoniae also inhibited th...
Colistin kills bacteria by targeting lipopolysaccharide in the cytoplasmic membrane
eLife
Colistin is an antibiotic of last resort, but has poor efficacy and resistance is a growing problem. Whilst it is well established that colistin disrupts the bacterial outer membrane (OM) by selectively targeting lipopolysaccharide (LPS), it was unclear how this led to bacterial killing. We discovered that MCR-1 mediated colistin resistance in Escherichia coli is due to modified LPS at the cytoplasmic rather than OM. In doing so, we also demonstrated that colistin exerts bactericidal activity by targeting LPS in the cytoplasmic membrane (CM). We then exploited this information to devise a new therapeutic approach. Using the LPS transport inhibitor murepavadin, we were able to cause LPS accumulation in the CM of Pseudomonas aeruginosa, which resulted in increased susceptibility to colistin in vitro and improved treatment efficacy in vivo. These findings reveal new insight into the mechanism by which colistin kills bacteria, providing the foundations for novel approaches to enhance th...
Nature microbiology, 2017
The increasing use of polymyxins(1) in addition to the dissemination of plasmid-borne colistin resistance threatens to cause a serious breach in our last line of defence against multidrug-resistant Gram-negative pathogens, and heralds the emergence of truly pan-resistant infections. Colistin resistance often arises through covalent modification of lipid A with cationic residues such as phosphoethanolamine-as is mediated by Mcr-1 (ref. 2)-which reduce the affinity of polymyxins for lipopolysaccharide(3). Thus, new strategies are needed to address the rapidly diminishing number of treatment options for Gram-negative infections(4). The difficulty in eradicating Gram-negative bacteria is largely due to their highly impermeable outer membrane, which serves as a barrier to many otherwise effective antibiotics(5). Here, we describe an unconventional screening platform designed to enrich for non-lethal, outer-membrane-active compounds with potential as adjuvants for conventional antibiotics...
Scientific Reports, 2018
With the dissemination of extremely drug resistant bacteria, colistin is now considered as the lastresort 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. Currently, antimicrobial resistance is on top of the agenda for scientists and governments, while pan-resistant organisms are fast emerging. Any lack of swift commitment and action to improve diagnostic and prevention would irremediably take us back to the dark age of dreadful and devastating epidemics. The pipeline of new antibiotics is very limited, and colistin is now considered as the last resort therapy for the treatment of infection caused by multidrug resistant (MDR) Gram-negative bacteria, such as carbapenemase-producing Acinetobacter baumannii 1. Unfortunately, with an increase in the use of colistin to treat carbapenem-resistant Acinetobacter baumannii infections, colistin resistance is emerging 2. In Gram-negative bacteria, acquired resistance to polymyxins results mostly from modifications of the drug target, i.e. the lipopolysaccharide (LPS). These modifications correspond to addition(s) of cationic groups such as 4-amino-L-arabinose (L-Ara4N) and/or phosphoethanolamine (pETN) on the lipid A, the anchor of the LPS. Unlike Enterobacteriaceae, A. baumannii lacks all the genes required for L-Ara4N biosynthesis. Accordingly, colistin resistance is caused by the addition of pETN to the lipid A on position 1 or 4' by an EptA-like phosphoethanolamine transferase chromosomally-encoded by the pmrC gene. As well, mutations in the chromosome-encoded pmrA and pmrB genes result in a constitutive activation of the PmrA/PmrB two-component system, which in turn upregulates the expression of pmrC 3-5. Recently, plasmid-mediated resistance to polymyxin, named MCR, was described in Enterobacteriaceae. The mcr genes (mcr-1,-2,-3,-4,-5,-6,-7 and-8) also encode a phosphoethanolamine transferase involved in addition of pETN on the lipid A 6. Although mcr genes were found to have
International Journal of Molecular Sciences
The nosocomial opportunistic Gram-negative bacterial pathogen Acinetobacter baumannii is resistant to multiple antimicrobial agents and an emerging global health problem. The polymyxin antibiotic colistin, targeting the negatively charged lipid A component of the lipopolysaccharide on the bacterial cell surface, is often considered as the last-resort treatment, but resistance to colistin is unfortunately increasing worldwide. Notably, colistin-susceptible A. baumannii can also develop a colistin dependence after exposure to this drug in vitro. Colistin dependence might represent a stepping stone to resistance also in vivo. However, the mechanisms are far from clear. To address this issue, we combined proteogenomics, high-resolution microscopy, and lipid profiling to characterize and compare A. baumannii colistin-susceptible clinical isolate (Ab-S) of to its colistin-dependent subpopulation (Ab-D) obtained after subsequent passages in moderate colistin concentrations. Incidentally, i...
Antimicrobial Agents and Chemotherapy, 2013
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ACS Infectious Diseases, 2019
Therapeutics targeting Gram-negative bacteria have the challenge of overcoming a formidable outer membrane (OM) barrier. Here, we characterize the action of SPR741, a novel polymyxin B (PMB) analogue shown to potentiate several large-scaffold antibiotics in Gram-negative pathogens. Probing the surface topology of Escherichia coli using atomic force microscopy revealed substantial OM disorder at concentrations of SPR741 that lead to antibiotic potentiation. Conversely, very little cytoplasmic membrane depolarization was observed at these same concentrations, indicating that SPR741 acts predominately on the OM. Truncating the lipopolysaccharide (LPS) core with genetic perturbations uniquely sensitized E. coli to SPR741, suggesting that LPS core residues keep SPR741 at the OM, where it can potentiate a codrug, rather than permit its entry to the cytoplasmic membrane. Further, a promoter activity assay revealed that SPR741 challenge induced the expression of RcsAB, a stress sensor for OM perturbation. Together, these results indicate that SPR741 interacts predominately with the OM, in contrast to the dual action of PMB and colistin at both the outer and cytoplasmic membranes.
PLOS ONE, 2017
Chronic bacterial biofilms place a massive burden on healthcare due to the presence of antibiotic-tolerant dormant bacteria. Some of the conventional antibiotics such as erythromycin, vancomycin, linezolid, rifampicin etc. are inherently ineffective against Gram-negative bacteria, particularly in their biofilms. Here, we report membrane-active macromolecules that kill slow dividing stationary-phase and antibiotic tolerant cells of Gram-negative bacteria. More importantly, these molecules potentiate antibiotics (erythromycin and rifampicin) to biofilms of Gram-negative bacteria. These molecules eliminate planktonic bacteria that are liberated after dispersion of biofilms (dispersed cells). The membrane-active mechanism of these molecules forms the key for potentiating the established antibiotics. Further, we demonstrate that the combination of macromolecules and antibiotics significantly reduces bacterial burden in mouse burn and surgical wound infection models caused by Acinetobacter baumannii and Carbapenemase producing Klebsiella pneumoniae (KPC) clinical isolate respectively. Colistin, a well-known antibiotic targeting the lipopolysaccharide (LPS) of Gram-negative bacteria fails to kill antibiotic tolerant cells and dispersed cells (from biofilms) and bacteria develop resistance to it. On the contrary, these macromolecules prevent or delay the development of bacterial resistance to known antibiotics. Our findings emphasize the potential of targeting the bacterial membrane in antibiotic potentiation for disruption of biofilms and suggest a promising strategy towards developing therapies for topical treatment of Gram-negative infections.