Amino acid addition to Vibrio cholerae LPS establishes a link between surface remodeling in gram-positive and gram-negative bacteria. - Related Documents




#
Rank
Similarity
Title + Abs.
Year
PMID
012345
821101.0000Amino acid addition to Vibrio cholerae LPS establishes a link between surface remodeling in gram-positive and gram-negative bacteria. Historically, the O1 El Tor and classical biotypes of Vibrio cholerae have been differentiated by their resistance to the antimicrobial peptide polymyxin B. However, the molecular mechanisms associated with this phenotypic distinction have remained a mystery for 50 y. Both gram-negative and gram-positive bacteria modify their cell wall components with amine-containing substituents to reduce the net negative charge of the bacterial surface, thereby promoting cationic antimicrobial peptide resistance. In the present study, we demonstrate that V. cholerae modify the lipid A anchor of LPS with glycine and diglycine residues. This previously uncharacterized lipid A modification confers polymyxin resistance in V. cholerae El Tor, requiring three V. cholerae proteins: Vc1577 (AlmG), Vc1578 (AlmF), and Vc1579 (AlmE). Interestingly, the protein machinery required for glycine addition is reminiscent of the gram-positive system responsible for D-alanylation of teichoic acids. Such machinery was not thought to be used by gram-negative organisms. V. cholerae O1 El Tor mutants lacking genes involved in transferring glycine to LPS showed a 100-fold increase in sensitivity to polymyxin B. This work reveals a unique lipid A modification and demonstrates a charge-based remodeling strategy shared between gram-positive and gram-negative organisms.201222589301
821410.9996The dlt operon confers resistance to cationic antimicrobial peptides in Clostridium difficile. The dlt operon in Gram-positive bacteria encodes proteins that are necessary for the addition of d-alanine to teichoic acids of the cell wall. The addition of d-alanine to the cell wall results in a net positive charge on the bacterial cell surface and, as a consequence, can decrease the effectiveness of antimicrobials, such as cationic antimicrobial peptides (CAMPs). Although the roles of the dlt genes have been studied for some Gram-positive organisms, the arrangement of these genes in Clostridium difficile and the life cycle of the bacterium in the host are markedly different from those of other pathogens. In the current work, we determined the contribution of the putative C. difficile dlt operon to CAMP resistance. Our data indicate that the dlt operon is necessary for full resistance of C. difficile to nisin, gallidermin, polymyxin B and vancomycin. We propose that the d-alanylation of teichoic acids provides protection against antimicrobial peptides that may be essential for growth of C. difficile in the host.201121330441
70420.9995Aminoarabinose is essential for lipopolysaccharide export and intrinsic antimicrobial peptide resistance in Burkholderia cenocepacia(†). One common mechanism of resistance against antimicrobial peptides in Gram-negative bacteria is the addition of 4-amino-4-deoxy-L-arabinose (L-Ara4N) to the lipopolysaccharide (LPS) molecule. Burkholderia cenocepacia exhibits extraordinary intrinsic resistance to antimicrobial peptides and other antibiotics. We have previously discovered that unlike other bacteria, B. cenocepacia requires L-Ara4N for viability. Here, we describe the isolation of B. cenocepacia suppressor mutants that remain viable despite the deletion of genes required for L-Ara4N synthesis and transfer to the LPS. The absence of L-Ara4N is the only structural difference in the LPS of the mutants compared with that of the parental strain. The mutants also become highly sensitive to polymyxin B and melittin, two different classes of antimicrobial peptides. The suppressor phenotype resulted from a single amino acid replacement (aspartic acid to histidine) at position 31 of LptG, a protein component of the multi-protein pathway responsible for the export of the LPS molecule from the inner to the outer membrane. We propose that L-Ara4N modification of LPS provides a molecular signature required for LPS export and proper assembly at the outer membrane of B. cenocepacia, and is the most critical determinant for the intrinsic resistance of this bacterium to antimicrobial peptides.201222742453
70130.9995Antimicrobial Peptide Resistance Genes in the Plant Pathogen Dickeya dadantii. Modification of teichoic acid through the incorporation of d-alanine confers resistance in Gram-positive bacteria to antimicrobial peptides (AMPs). This process involves the products of the dltXABCD genes. These genes are widespread in Gram-positive bacteria, and they are also found in a few Gram-negative bacteria. Notably, these genes are present in all soft-rot enterobacteria (Pectobacterium and Dickeya) whose dltDXBAC operons have been sequenced. We studied the function and regulation of these genes in Dickeya dadantii dltB expression was induced in the presence of the AMP polymyxin. It was not regulated by PhoP, which controls the expression of some genes involved in AMP resistance, but was regulated by ArcA, which has been identified as an activator of genes involved in AMP resistance. However, arcA was not the regulator responsible for polymyxin induction of these genes in this bacterium, which underlines the complexity of the mechanisms controlling AMP resistance in D. dadantii Two other genes involved in resistance to AMPs have also been characterized, phoS and phoH dltB, phoS, phoH, and arcA but not dltD mutants were more sensitive to polymyxin than the wild-type strain. Decreased fitness of the dltB, phoS, and phoH mutants in chicory leaves indicates that their products are important for resistance to plant AMPs. IMPORTANCE: Gram-negative bacteria can modify their lipopolysaccharides (LPSs) to resist antimicrobial peptides (AMPs). Soft-rot enterobacteria (Dickeya and Pectobacterium spp.) possess homologues of the dlt genes in their genomes which, in Gram-positive bacteria, are involved in resistance to AMPs. In this study, we show that these genes confer resistance to AMPs, probably by modifying LPSs, and that they are required for the fitness of the bacteria during plant infection. Two other new genes involved in resistance were also analyzed. These results show that bacterial resistance to AMPs can occur in bacteria through many different mechanisms that need to be characterized.201627565623
443940.9994beta-lactam resistance in Streptococcus pneumoniae: penicillin-binding proteins and non-penicillin-binding proteins. The beta-lactams are by far the most widely used and efficacious of all antibiotics. Over the past few decades, however, widespread resistance has evolved among most common pathogens. Streptococcus pneumoniae has become a paradigm for understanding the evolution of resistance mechanisms, the simplest of which, by far, is the production of beta-lactamases. As these enzymes are frequently plasmid encoded, resistance can readily be transmitted between bacteria. Despite the fact that pneumococci are naturally transformable organisms, no beta-lactamase-producing strain has yet been described. A much more complex resistance mechanism has evolved in S. pneumoniae that is mediated by a sophisticated restructuring of the targets of the beta-lactams, the penicillin-binding proteins (PBPs); however, this may not be the whole story. Recently, a third level of resistance mechanisms has been identified in laboratory mutants, wherein non-PBP genes are mutated and resistance development is accompanied by deficiency in genetic transformation. Two such non-PBP genes have been described: a putative glycosyltransferase, CpoA, and a histidine protein kinase, CiaH. We propose that these non-PBP genes are involved in the biosynthesis of cell wall components at a step prior to the biosynthetic functions of PBPs, and that the mutations selected during beta-lactam treatment counteract the effects caused by the inhibition of penicillin-binding proteins.199910447877
70350.9994Bacterial modification of LPS and resistance to antimicrobial peptides. Antimicrobial peptides (APs) are ubiquitous in nature and are thought to kill micro-organisms by affecting membrane integrity. These positively charged peptides interact with negative charges in the LPS of Gram-negative bacteria. A common mechanism of resistance to AP killing is LPS modification. These modifications include fatty acid additions, phosphoethanolamine (PEtN) addition to the core and lipid A regions, 4-amino-4-deoxy-L-arabinose (Ara4N) addition to the core and lipid A regions, acetylation of the O-antigen, and possibly hydroxylation of fatty acids. In Salmonella typhimurium, LPS modifications are induced within host tissues by the two-component regulatory systems PhoPQ and PmrAB. PmrAB activation results in AP resistance by Ara4N addition to lipid A through the activation of at least 8 genes, 7 of which are transcribed as an operon. Loss of this operon and, therefore, Ara4N LPS modification, affects S. typhimurium virulence when administered orally. Transposon mutagenesis of Proteus mirabilis also suggests that LPS modifications affect AP resistance and virulence phenotypes. Therefore, LPS modification in Gram-negative bacteria plays a significant role during infection in resistance to host antimicrobial factors, avoidance of immune system recognition, and maintenance of virulence phenotypes.200111521084
70260.9994Cutting edge: the toll pathway is required for resistance to gram-positive bacterial infections in Drosophila. In Drosophila, the response against various microorganisms involves different recognition and signaling pathways, as well as distinct antimicrobial effectors. On the one hand, the immune deficiency pathway regulates the expression of antimicrobial peptides that are active against Gram-negative bacteria. On the other hand, the Toll pathway is involved in the defense against filamentous fungi and controls the expression of antifungal peptide genes. The gene coding for the only known peptide with high activity against Gram-positive bacteria, Defensin, is regulated by both pathways. So far, survival experiments to Gram-positive bacteria have been performed with Micrococcus luteus and have failed to reveal the involvement of one or the other pathway in host defense against such infections. In this study, we report that the Toll pathway, but not that of immune deficiency, is required for resistance to other Gram-positive bacteria and that this response does not involve Defensin.200211823479
22570.9994Mechanisms of bactericidal action and resistance of polymyxins for Gram-positive bacteria. Polymyxins are cationic antimicrobial peptides used as the last-line therapy to treat multidrug-resistant Gram-negative bacterial infections. The bactericidal activity of polymyxins against Gram-negative bacteria relies on the electrostatic interaction between the positively charged polymyxins and the negatively charged lipid A of lipopolysaccharide (LPS). Given that Gram-positive bacteria lack an LPS-containing outer membrane, it is generally acknowledged that polymyxins are less active against Gram-positive bacteria. However, Gram-positive bacteria produce negatively charged teichoic acids, which may act as the target of polymyxins. More and more studies suggest that polymyxins have potential as a treatment for Gram-positive bacterial infection. This mini-review discusses recent advances in the mechanism of the antibacterial activity and resistance of polymyxins in Gram-positive bacteria.Key Points• Teichoic acids play a key role in the action of polymyxins on Gram-positive bacteria.• Polymyxin kills Gram-positive bacteria by disrupting cell surface and oxidative damage.• Modification of teichoic acids and phospholipids contributes to polymyxin resistance in Gram-positive bacteria.• Polymyxins have potential as a treatment for Gram-positive bacterial infection.202032157424
821580.9994Insight into Two ABC Transporter Families Involved in Lantibiotic Resistance. Antimicrobial peptides, which contain (methyl)-lanthionine-rings are called lantibiotics. They are produced by several Gram-positive bacteria and are mainly active against these bacteria. Although these are highly potent antimicrobials, some human pathogenic bacteria express specific ABC transporters that confer resistance and counteract their antimicrobial activity. Two distinct ABC transporter families are known to be involved in this process. These are the Cpr- and Bce-type ABC transporter families, named after their involvement in cationic peptide resistance in Clostridium difficile, and bacitracin efflux in Bacillus subtilis, respectively. Both resistance systems differentiate to each other in terms of the proteins involved. Here, we summarize the current knowledge and describe the divergence as well as the common features present in both the systems to confer lantibiotic resistance.201729404338
443690.9994Bacterial resistance to vancomycin: five genes and one missing hydrogen bond tell the story. A plasmid-borne transposon encodes enzymes and regulator proteins that confer resistance of enterococcal bacteria to the antibiotic vancomycin. Purification and characterization of individual proteins encoded by this operon has helped to elucidate the molecular basis of vancomycin resistance. This new understanding provides opportunities for intervention to reverse resistance.19968807824
8212100.9994The biosynthesis and functionality of the cell-wall of lactic acid bacteria. The cell wall of lactic acid bacteria has the typical gram-positive structure made of a thick, multilayered peptidoglycan sacculus decorated with proteins, teichoic acids and polysaccharides, and surrounded in some species by an outer shell of proteins packed in a paracrystalline layer (S-layer). Specific biochemical or genetic data on the biosynthesis pathways of the cell wall constituents are scarce in lactic acid bacteria, but together with genomics information they indicate close similarities with those described in Escherichia coli and Bacillus subtilis, with one notable exception regarding the peptidoglycan precursor. In several species or strains of enterococci and lactobacilli, the terminal D-alanine residue of the muramyl pentapeptide is replaced by D-lactate or D-serine, which entails resistance to the glycopeptide antibiotic vancomycin. Diverse physiological functions may be assigned to the cell wall, which contribute to the technological and health-related attributes of lactic acid bacteria. For instance, phage receptor activity relates to the presence of specific substituents on teichoic acids and polysaccharides; resistance to stress (UV radiation, acidic pH) depends on genes involved in peptidoglycan and teichoic acid biosynthesis; autolysis is controlled by the degree of esterification of teichoic acids with D-alanine; mucosal immunostimulation may result from interactions between epithelial cells and peptidoglycan or teichoic acids.199910532377
292110.9994Mechanisms underlying expression of Tn10 encoded tetracycline resistance. Tetracycline-resistance determinants encoding active efflux of the drug are widely distributed in gram-negative bacteria and unique with respect to genetic organization and regulation of expression. Each determinant consists of two genes called tetA and tetR, which are oriented with divergent polarity, and between them is a central regulatory region with overlapping promoters and operators. The amino acid sequences of the encoded proteins are 43-78% identical. The resistance protein TetA is a tetracycline/metal-proton antiporter located in the cytoplasmic membrane, while the regulatory protein TetR is a tetracycline inducible repressor. TetR binds via a helix-turn-helix motif to the two tet operators, resulting in repression of both genes. A detailed model of the repressor-operator complex has been proposed on the basis of biochemical and genetic data. The tet genes are differentially regulated so that repressor synthesis can occur before the resistance protein is expressed. This has been demonstrated for the Tn10-encoded tet genes and may be a common property of all tet determinants, as suggested by the similar locations of operators with respect to promoters. Induction is mediated by a tetracycline-metal complex and requires only nanomolar concentrations of the drug. This is the most sensitive effector-inducible system of transcriptional regulation known to date. The crystal structure of the TetR-tetracycline/metal complex shows the Tet repressor in the induced, non-DNA binding conformation. The structural interpretation of many noninducible TetR mutants has offered insight into the conformational changes associated with the switch between inducing and repressing structures of TetR. Tc is buried in the core of TetR, where it is held in place by multiple contacts to the protein.19947826010
8229120.9994Molecular genetics, biochemistry and biological role of Yersinia lipopolysaccharide. Lipopolysaccharide (LPS) is the major component of the outer leaflet of the outer membrane of Gram-negative bacteria. The LPS molecule is composed of two biosynthetic entities: the lipid A--core and the O-polysaccharide (O-antigen). Most biological effects of LPS are due to the lipid A part, however, there is an increasing body of evidence also with Yersinia indicating that O-antigen plays an important role in effective colonization of host tissues, resistance to complement-mediated killing and in the resistance to cationic antimicrobial peptides that are key elements of the innate immune system. The biosynthesis of O-antigen requires numerous enzymatic activities and includes the biosynthesis of individual NDP-activated precursor sugars in the cytoplasm, linkage and sugar-specific transferases, O-unit flippase, O-antigen polymerase and O-chain length determinant. Based on this enzymatic mode of O-antigen biosynthesis LPS isolated from bacteria is a heterologous population of molecules; some do not carry any O-antigen while others that do have variation in the O-antigen chain lengths. The genes required for the O-antigen biosynthesis are located in O-antigen gene clusters that in genus Yersinia is located between the hemH and gsk genes. Temperature regulates the O-antigen expression in Y. enterocolitica and Y. pseudotuberculosis; bacteria grown at room temperature (RT, 22-25 degrees C) produce in abundance O-antigen while only trace amounts are present in bacteria grown at 37 degrees C. Even though the amount of O-antigen is known to fluctuate under different growth conditions in many bacteria very little detailed information is available on the control of the O-antigen biosynthetic machinery.200312756756
9779130.9994Mechanisms 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.201931364071
6316140.9994A novel type of colistin resistance genes selected from random sequence space. Antibiotic resistance is a rapidly increasing medical problem that severely limits the success of antibiotic treatments, and the identification of resistance determinants is key for surveillance and control of resistance dissemination. Horizontal transfer is the dominant mechanism for spread of resistance genes between bacteria but little is known about the original emergence of resistance genes. Here, we examined experimentally if random sequences can generate novel antibiotic resistance determinants de novo. By utilizing highly diverse expression libraries encoding random sequences to select for open reading frames that confer resistance to the last-resort antibiotic colistin in Escherichia coli, six de novo colistin resistance conferring peptides (Dcr) were identified. The peptides act via direct interactions with the sensor kinase PmrB (also termed BasS in E. coli), causing an activation of the PmrAB two-component system (TCS), modification of the lipid A domain of lipopolysaccharide and subsequent colistin resistance. This kinase-activation was extended to other TCS by generation of chimeric sensor kinases. Our results demonstrate that peptides with novel activities mediated via specific peptide-protein interactions in the transmembrane domain of a sensory transducer can be selected de novo, suggesting that the origination of such peptides from non-coding regions is conceivable. In addition, we identified a novel class of resistance determinants for a key antibiotic that is used as a last resort treatment for several significant pathogens. The high-level resistance provided at low expression levels, absence of significant growth defects and the functionality of Dcr peptides across different genera suggest that this class of peptides could potentially evolve as bona fide resistance determinants in natura.202133411736
706150.9994Effect of PhoP-PhoQ activation by broad repertoire of antimicrobial peptides on bacterial resistance. Pathogenic bacteria can resist their microenvironment by changing the expression of virulence genes. In Salmonella typhimurium, some of these genes are controlled by the two-component system PhoP-PhoQ. Studies have shown that activation of the system by cationic antimicrobial peptides (AMPs) results, among other changes, in outer membrane remodeling. However, it is not fully clear what characteristics of AMPs are required to activate the PhoP-PhoQ system and whether activation can induce resistance to the various AMPs. For that purpose, we investigated the ability of a broad repertoire of AMPs to traverse the inner membrane, to activate the PhoP-PhoQ system, and to induce bacterial resistance. The AMPs differ in length, composition, and net positive charge, and the tested bacteria include two wild-type (WT) Salmonella strains and their corresponding PhoP-PhoQ knock-out mutants. A lacZ-reporting system was adapted to follow PhoP-PhoQ activation. The data revealed that: (i) a good correlation exists among the extent of the positive charge, hydrophobicity, and amphipathicity of an AMP and its potency to activate PhoP-PhoQ; (ii) a +1 charged peptide containing histidines was highly potent, suggesting the existence of an additional mechanism independent of the peptide charge; (iii) the WT bacteria are more resistant to AMPs that are potent activators of PhoP-PhoQ; (iv) only a subset of AMPs, independent of their potency to activate the system, is more toxic to the mutated bacteria compared with the WT strains; and (v) short term exposure of WT bacteria to these AMPs does not enhance resistance. Overall, this study advances our understanding of the molecular mechanism by which AMPs activate PhoP-PhoQ and induce bacterial resistance. It also reveals that some AMPs can overcome such a resistance mechanism.201222158870
6342160.9994Determinants of Extreme β-Lactam Tolerance in the Burkholderia pseudomallei Complex. Slow-growing bacteria are insensitive to killing by antibiotics, a trait known as antibiotic tolerance. In this study, we characterized the genetic basis of an unusually robust β-lactam (meropenem) tolerance seen in Burkholderia species. We identified tolerance genes under three different slow-growth conditions by extensive transposon mutant sequencing (Tn-seq), followed by single mutant validation. There were three principal findings. First, mutations in a small number of genes reduced tolerance under multiple conditions. Most of the functions appeared to be specific to peptidoglycan synthesis and the response to its disruption by meropenem action rather than being associated with more general physiological processes. The top tolerance genes are involved in immunity toward a type VI toxin targeting peptidoglycan (BTH_I0069), peptidoglycan recycling (ldcA), periplasmic regulation by proteolysis (prc), and an envelope stress response (rpoE and degS). Second, most of the tolerance functions did not contribute to growth in the presence of meropenem (intrinsic resistance), indicating that the two traits are largely distinct. Third, orthologues of many of the top Burkholderia thailandensis tolerance genes were also important in Burkholderia pseudomallei Overall, these studies show that the determinants of meropenem tolerance differ considerably depending on cultivation conditions, but that there are a few shared functions with strong mutant phenotypes that are important in multiple Burkholderia species.201829439964
8924170.9994Genomic Signatures of Experimental Adaptation to Antimicrobial Peptides in Staphylococcus aureus. The evolution of resistance against antimicrobial peptides has long been considered unlikely due to their mechanism of action, yet experimental selection with antimicrobial peptides (AMPs) results in rapid evolution of resistance in several species of bacteria. Although numerous studies have utilized mutant screens to identify loci that determine AMP susceptibility, there is a dearth of data concerning the genomic changes that accompany experimental evolution of AMP resistance. Using genome resequencing, we analyzed the mutations that arose during experimental evolution of resistance to the cationic AMPs iseganan, melittin, and pexiganan, as well as to a combination of melittin and pexiganan, or to the aminoglycoside antibiotic streptomycin. Analysis of 17 independently replicated Staphylococcus aureus selection lines, including unselected controls, showed that each AMP selected for mutations at distinct loci. We identify mutations in genes involved in the synthesis and maintenance of the cell envelope. These include genes previously identified from mutant screens for AMP resistance, and genes involved in the response to AMPs and cell-wall-active antibiotics. Furthermore, transposon insertion mutants were used to verify that a number of the identified genes are directly involved in determining AMP susceptibility. Strains selected for AMP resistance under controlled experimental evolution displayed consistent AMP-specific mutations in genes that determine AMP susceptibility. This suggests that different routes to evolve resistance are favored within a controlled genetic background.201627172179
6217180.9994Identification of the sigmaB regulon of Bacillus cereus and conservation of sigmaB-regulated genes in low-GC-content gram-positive bacteria. The alternative sigma factor sigma(B) has an important role in the acquisition of stress resistance in many gram-positive bacteria, including the food-borne pathogen Bacillus cereus. Here, we describe the identification of the set of sigma(B)-regulated genes in B. cereus by DNA microarray analysis of the transcriptome upon a mild heat shock. Twenty-four genes could be identified as being sigma(B) dependent as witnessed by (i) significantly lower expression levels of these genes in mutants with a deletion of sigB and rsbY (which encode the alternative sigma factor sigma(B) and a crucial positive regulator of sigma(B) activity, respectively) than in the parental strain B. cereus ATCC 14579 and (ii) increased expression of these genes upon a heat shock. Newly identified sigma(B)-dependent genes in B. cereus include a histidine kinase and two genes that have predicted functions in spore germination. This study shows that the sigma(B) regulon of B. cereus is considerably smaller than that of other gram-positive bacteria. This appears to be in line with phylogenetic analyses where sigma(B) of the B. cereus group was placed close to the ancestral form of sigma(B) in gram-positive bacteria. The data described in this study and previous studies in which the complete sigma(B) regulon of the gram-positive bacteria Bacillus subtilis, Listeria monocytogenes, and Staphylococcus aureus were determined enabled a comparison of the sets of sigma(B)-regulated genes in the different gram-positive bacteria. This showed that only three genes (rsbV, rsbW, and sigB) are conserved in their sigma(B) dependency in all four bacteria, suggesting that the sigma(B) regulon of the different gram-positive bacteria has evolved to perform niche-specific functions.200717416654
6317190.9994O-specific polysaccharide confers lysozyme resistance to extraintestinal pathogenic Escherichia coli. Extraintestinal pathogenic Escherichia coli (ExPEC) is the leading cause of bloodstream and other extraintestinal infections in human and animals. The greatest challenge encountered by ExPEC during an infection is posed by the host defense mechanisms, including lysozyme. ExPEC have developed diverse strategies to overcome this challenge. The aim of this study was to characterize the molecular mechanism of ExPEC resistance to lysozyme. For this, 15,000 transposon mutants of a lysozyme-resistant ExPEC strain NMEC38 were screened; 20 genes were identified as involved in ExPEC resistance to lysozyme-of which five were located in the gene cluster between galF and gnd, and were further confirmed to be involved in O-specific polysaccharide biosynthesis. The O-specific polysaccharide was able to inhibit the hydrolytic activity of lysozyme; it was also required by the complete lipopolysaccharide (LPS)-mediated protection of ExPEC against the bactericidal activity of lysozyme. The O-specific polysaccharide was further shown to be able to directly interact with lysozyme. Furthermore, LPS from ExPEC strains of different O serotypes was also able to inhibit the hydrolytic activity of lysozyme. Because of their cell surface localization and wide distribution in Gram-negative bacteria, O-specific polysaccharides appear to play a long-overlooked role in protecting bacteria against exogenous lysozyme.201829405825