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The intestinal microbiome modulates host susceptibility to enteric pathogens, but the specific protective factors and mechanisms of individual bacterial species are not fully characterized. We show that secreted antigen A (SagA) from Enterococcus faecium is sufficient to protect Caenorhabditis elegans against Salmonella pathogenesis by promoting pathogen tolerance. The NlpC/p60 peptidoglycan hydrolase activity of SagA is required and generates muramylpeptide fragments that are sufficient to protect C. elegans against Salmonella pathogenesis in a tol-1-dependent manner. SagA can also be heterologously expressed and secreted to improve the protective activity of probiotics against Salmonella pathogenesis in C. elegans and mice. Our study highlights how protective intestinal bacteria can modify microbialassociated molecular patterns to enhance pathogen tolerance.

Multidrug-resistant bacterial pathogens like vancomycin-resistant Enterococcus faecium (VREfm) are a critical threat to human health 1 . Daptomycin is a last-resort antibiotic for VREfm infections with a novel mode of action 2 , but for which resistance has been widely reported but is unexplained. Here we show that rifaximin, an unrelated antibiotic used prophylactically to prevent hepatic encephalopathy in patients with liver disease 3 , causes cross-resistance to daptomycin in VREfm. Amino acid changes arising within the bacterial RNA polymerase in response to rifaximin exposure cause upregulation of a previously uncharacterized operon ( prdRAB ) that leads to cell membrane remodelling and cross-resistance to daptomycin through reduced binding of the antibiotic. VREfm with these mutations are spread globally, making this a major mechanism of resistance. Rifaximin has been considered ‘low risk’ for the development of antibiotic resistance. Our study shows that this assumption is flawed and that widespread rifaximin use, particularly in patients with liver cirrhosis, may be compromising the clinical use of daptomycin, a major last-resort intervention for multidrug-resistant pathogens. These findings demonstrate how unanticipated antibiotic cross-resistance can undermine global strategies designed to preserve the clinical use of critical antibiotics. Rifaximin use, particularly in patients with liver cirrhosis, may be compromising the clinical use of daptomycin.

The peptidoglycan (PG) layer stabilizes the bacterial cell envelope to maintain the integrity and shape of the cell. Penicillin-binding proteins (PBPs) synthesize essential 4–3 cross-links in PG and are inhibited by β-lactam antibiotics. Some clinical isolates and laboratory strains of Enterococcus faecium and Escherichia coli achieve high-level β-lactam resistance by utilizing β-lactam–insensitive LD-transpeptidases (LDTs) to produce exclusively 3–3 cross-links in PG, bypassing the PBPs. In E. coli, other LDTs covalently attach the lipoprotein Lpp to PG to stabilize the envelope and maintain the permeability barrier function of the outermembrane. Here we show that subminimal inhibitory concentration of copper chloride sensitizes E. coli cells to sodium dodecyl sulfate and impair survival upon LPS transport stress, indicating reduced cell envelope robustness. Cells grown in the presence of copper chloride lacked 3–3 cross-links in PG and displayed reduced covalent attachment of Braun’s lipoprotein and reduced incorporation of a fluorescent D-amino acid, suggesting inhibition of LDTs. Copper dramatically decreased the minimal inhibitory concentration of ampicillin in E. coli and E. faecium strains with a resistance mechanism relying on LDTs and inhibited purified LDTs at submillimolar concentrations. Hence, our work reveals how copper affects bacterial cell envelope stability and counteracts LDT-mediated β-lactam resistance.

We discovered that Enterococcus faecium (E. faecium), a ubiquitous commensal bacterium, and its secreted peptidoglycan hydrolase (SagA) were sufficient to enhance intestinal barrier function and pathogen tolerance, but the precise biochemical mechanism was unknown. Here we show E. faecium has unique peptidoglycan composition and remodeling activity through SagA, which generates smaller muropeptides that more effectively activates nucleotide-binding oligomerization domain-containing protein 2 (NOD2) in mammalian cells. Our structural and biochemical studies show that SagA is a NlpC/p60-endopeptidase that preferentially hydrolyzes crosslinked Lys-type peptidoglycan fragments. SagA secretion and NlpC/p60-endopeptidase activity was required for enhancing probiotic bacteria activity against Clostridium difficile pathogenesis in vivo. Our results demonstrate that the peptidoglycan composition and hydrolase activity of specific microbiota species can activate host immune pathways and enhance tolerance to pathogens.

The rapid utilization of fossil fuel-based energy sources increased demand for alternate sustainable energy sources. One of the best alternate energy sources can be lignocellulosic biomass. The major constituent of lignocellulosic biomass is cellulose that can be converted into simple sugar using cellulase enzymes followed by fermentation for ethanol production. Two potential mesophilic cellulolytic bacteria, BS5 and CS7, from brinjal and cotton soil samples were screened based on high zones of hydrolysis on CMC agar plates and identified as Enterococcus faecium and Stutzerimonas stutzeri , respectively. It is the first instance of a mesophilic cellulase being reported from an S. stutzeri . CMCase production was enhanced by methods like one factor at a time (OFAT) and response surface methodology (RSM). The optimal conditions for maximum CMCase production by isolate BS5 were pH 5.0, 41℃, 1.25% inocula volume, and 56 h of incubation, whereas isolate CS7 produced maximum CMCase at pH 7.0, 43℃, 2.0% inocula volume, and 42 h of incubation. Following optimization through RSM-CCD, CMCase productivity of isolate BS5 increased 2.43 times, reaching 20.4 U/mL compared to 8.22 U/mL under unoptimized conditions, while CMCase productivity of isolate CS7 increased 2.18 times, reaching 24.08 U/mL compared to initial unoptimized activity of 11.05 U/mL. The crude enzyme produced by both isolates demonstrated effective potential in biopolishing cotton fabrics. Cotton fabrics treated with crude enzymes from BS5 and CS7 isolates lost 2.20% and 2.06% of their weight, respectively, showing that the enzymes removed tiny fibers from the surface of the cotton, making it smoother. Crude enzyme of both isolates showed optimum activity at mesophilic temperature, which makes them suitable for industrial applications like bioethanol production using simultaneous saccharification and fermentation, biopolishing and biostoning in the textile industry, and deinking in the paper and pulp industry.

Enterococcus faecium is a common cause of nosocomial infections, of which infective endocarditis is associated with substantial mortality. In this study, we used a microarray-based transposon mapping (M-TraM) approach to evaluate a rat endocarditis model and identified a gene, originally annotated as \"fruA\" and renamed \"bepA\" putatively encoding a carbohydrate phosphotransferase system (PTS) permease (biofilm and endocarditis-associated permease A [BepA]), as important in infective endocarditis. This gene is highly enriched in E. faecium clinical isolates and absent in commensal isolates that are not associated with infection. Confirmation of the phenotype was established in a competition experiment of wild-type and a markerless bepA mutant in a rat endocarditis model. In addition, deletion of bepA impaired biofilm formation in vitro in the presence of 100% human serum and metabolism of β-methyl-D-glucoside. β-D-glucoside metabolism has been linked to the metabolism of glycosaminoglycans that are exposed on injured heart valves, where bacteria attach and form vegetations. Therefore, we propose that the PTS permease BepA is directly implicated in E. faecium pathogenesis.

Bile salt hydrolase (BSH), a probiotic-related enzyme with cholesterol-assimilating and anti-hypercholesterolemic abilities, has been isolated from intestinal bacteria; however, BSH activity of bacteria in bile-salt-free (non-intestinal) environments is largely unknown. Here, we aimed to identify BSH from non-intestinal Enterococcus faecium and characterize its enzymatic function. We successfully isolated a plasmid-encoded bsh (efpBSH) from E. faecium, and the recombinant EfpBSH showed BSH activity that preferentially hydrolyzed taurine-conjugated bile salts, unlike the activity of known BSHs. EfpBSH functioned optimally at pH 4.0 and 50 °C. EfpBSH exhibited very low amino acid sequence similarity (48.46%) to EfBSH from E. faecalis T2 isolated from human urine, although 241 sequences with 100% identity to EfpBSH were found in both plasmids and chromosomes of E. faecium strains inhabiting intestinal and non-intestinal environments. Phylogenetically, EfpBSH was not affiliated with any known BSH phylogroup and was clearly distinguished from previously identified BSHs from intestinal lactic acid bacteria. Our genome database analysis demonstrated that horizontal gene transfer causes global efpBSH distribution among E. faecium strains in various environments (soil, water, and intestinal samples) and geographical regions (Asia, Africa, Europe, North America, South America, and Australia/Oceania). Overall, our findings are the first to indicate that BSH is not an intestine-specific enzyme and that hitherto-overlooked probiotic candidates with BSH activity can exist in diverse environments.

Infections with antimicrobial resistant pathogens are a major threat to human health. Inhibitors of the replicative polymerase PolC are a promising novel class of antimicrobials against Gram-positive pathogens, but the structural basis for their activity remains unknown. The first-in-class PolC-targeting antimicrobial, ibezapolstat, is a guanine analogue in late-stage clinical development for the treatment of Clostridioides difficile infections, and related inhibitors are being developed for systemic treatment of infections with methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). Here, we present the cryo-electron microscopy structures of Enterococcus faecium PolC bound to DNA and in complex with ibezapolstat or the previously-undescribed inhibitor ACX-801. Both inhibitors form base-pairing interactions with the DNA in the active site, thereby competing with incoming dGTP nucleotides. We identify a crucial susceptibility determinant in PolC that is conserved in other organisms, such as C. difficile . This is explained by an unusual non-planar conformation of the inhibitors that induce a binding pocket in PolC. By combining structural, biochemical, bioinformatic and genetic analyses, this work lays the foundation for the rational development of an innovative class of antimicrobials against Gram-positive priority pathogens. In this work, Urem et al. characterize the mode of action as well as mechanism of reduced susceptibility related to a class of antimicrobials that is in development for the treatment of infections with Gram-positive pathogens.

This work provides the first crystallographically confirmed Mn² + -dependent arylsulfatase, unveiling a unique “windmill-like” homotetrameric architecture and demonstrating catalytic promiscuity toward sulfates, phosphates, and phosphonates. These findings address longstanding uncertainties about metal specificity in arylsulfatases, highlight the structural and functional diversity of the alkaline phosphatase superfamily, and suggest new strategies for modulating the sulfation of bioactive molecules.

Background Previous reports have demonstrated two thiazolidione derivatives (H2-60 and H2-81) can robustly inhibit the planktonic growth and biofilm formation of S. epidermidis and S. aureus by targeting the histidine kinase YycG . Whereas the antibacterial and anti-biofilm activity of these two thiazolidione derivatives (H2-60 and H2-81) against Enterococcus faecium remains elusive. Here, the pET28a-YycG recombinant plasmid were in vitro expressed in E. coli competent cell BL21 (DE3) and induced to express YycG’ protein (conding HisKA and HATPase_c domain) by 0.5 mM IPTG and was purified by Ni – NTA agarose and then for the autophosphorylation test. Antimicrobial testing and time-killing assay were also be determined. Anti-biofilm activity of two derivatives with sub-MIC concentration towards positive biofilm producers of clinical E. faecium were detected using polystyrene microtiter plate and CLSM. Results The MICs of H2-60 and H2-81 in the clinical isolates of E. faecium were in the range from 3.125 mg/L to 25 mg/L. Moreover, either H2-60 or H2-81 showed the excellent bactericidal activity against E. faecium with monotherapy or its combination with daptomycin by time-killing assay. E. faecium planktonic cells can be decreased by H2-60 or H2-81 for more than 3 × log10 CFU/mL after 24 h treatment when combined with daptomycin. Furthermore, over 90% of E. faecium biofilm formation could markedly be inhibited by H2-60 and H2-81 at 1/4 × MIC value. In addition, the frequency of the eradicated viable cells embedded in mature biofilm were evaluated by the confocal laser microscopy, suggesting that of H2-60 combined with ampicillin or daptomycin was significantly high when compared with single treatment (78.17 and 74.48% vs. 41.59%, respectively, P  < 0.01). Conclusion These two thiazolidione derivatives (H2-60 and H2-81) could directly impact the kinase phosphoration activity of YycG of E. faecium . H2-60 combined with daptomycin exhibit the excellent antibacterial and anti-biofilm activity against E. faecium by targeting YycG.