Molecular basis for dual functions in pilus assembly modulated by the lid of a pilus-specific sortase.

The biphasic assembly of Gram-positive pili begins with the covalent polymerization of distinct pilins catalyzed by a pilus-specific sortase, followed by the cell wall anchoring of the resulting polymers mediated by the housekeeping sortase. In Actinomyces oris, the pilus-specific sortase SrtC2 not only polymerizes FimA pilins to assemble type 2 fimbriae with CafA at the tip, but it can also act as the anchoring sortase, linking both FimA polymers and SrtC1-catalyzed FimP polymers (type 1 fimbriae) to peptidoglycan when the housekeeping sortase SrtA is inactive. To date, the structure-function determinants governing the unique substrate specificity and dual enzymatic activity of SrtC2 have not been illuminated. Here, we present the crystal structure of SrtC2 solved to 2.10-Å resolution. SrtC2 harbors a canonical sortase fold and a lid typical for class C sortases and additional features specific to SrtC2. Structural, biochemical, and mutational analyses of SrtC2 reveal that the extended lid of SrtC2 modulates its dual activity. Specifically, we demonstrate that the polymerizing activity of SrtC2 is still maintained by alanine-substitution, partial deletion, and replacement of the SrtC2 lid with the SrtC1 lid. Strikingly, pilus incorporation of CafA is significantly reduced by these mutations, leading to compromised polymicrobial interactions mediated by CafA. In a srtA mutant, the partial deletion of the SrtC2 lid reduces surface anchoring of FimP polymers, and the lid-swapping mutation enhances this process, while both mutations diminish surface anchoring of FimA pili. Evidently, the extended lid of SrtC2 enables the enzyme the cell wall-anchoring activity in a substrate-selective fashion.

The basal and major pilins in the Corynebacterium diphtheriae SpaA pilus adopt similar structures that competitively react with the pilin polymerase.

Many species of pathogenic gram-positive bacteria display covalently crosslinked protein polymers (called pili or fimbriae) that mediate microbial adhesion to host tissues. These structures are assembled by pilus-specific sortase enzymes that join the pilin components together via lysine-isopeptide bonds. The archetypal SpaA pilus from Corynebacterium diphtheriae is built by the Cd SrtA pilus-specific sortase, which crosslinks lysine residues within the SpaA and SpaB pilins to build the shaft and base of the pilus, respectively. Here, we show that Cd SrtA crosslinks SpaB to SpaA via a K139(SpaB)-T494(SpaA) lysine-isopeptide bond. Despite sharing only limited sequence homology, an NMR structure of SpaB reveals striking similarities with the N-terminal domain of SpaA (N SpaA) that is also crosslinked by Cd SrtA. In particular, both pilins contain similarly positioned reactive lysine residues and adjacent disordered AB loops that are predicted to be involved in the recently proposed "latch" mechanism of isopeptide bond formation. Competition experiments using an inactive SpaB variant and additional NMR studies suggest that SpaB terminates SpaA polymerization by outcompeting N SpaA for access to a shared thioester enzyme-substrate reaction intermediate.

Endoscopic variceal ligation versus propranolol for the primary prevention of oesophageal variceal bleeding in patients with hepatocellular carcinoma: an open-label, two-centre, randomised controlled trial.

OBJECTIVE: This randomised trial aimed to address whether endoscopic variceal ligation (EVL) or propranolol (PPL) is more effective at preventing initial oesophageal variceal bleeding (EVB) in patients with hepatocellular carcinoma (HCC). DESIGN: Patients with HCC and medium-to-large oesophageal varices (EVs) but without previous EVB were randomised to receive EVL (every 3-4 weeks until variceal eradication) or PPL (up to 320 mg daily) at a 1:1 ratio. Long-term follow-up data on EVB, other upper gastrointestinal bleeding (UGIB), non-bleeding liver decompensation, overall survival (OS) and adverse events (AEs) were analysed using competing risk regression. RESULTS: Between June 2011 and April 2021, 144 patients were randomised to receive EVL (n=72) or PPL (n=72). In the EVL group, 7 patients experienced EVB, and 30 died; in the PPL group, 19 patients had EVB, and 40 died. The EVL group had a lower cumulative incidence of EVB (Gray's test, p=0.009) than its counterpart, with no mortality difference (Gray's test, p=0.085). For patients with Barcelona Clinic Liver Cancer (BCLC) stage A/B, EVL was better than PPL in reducing EVB (p<0.001) and mortality (p=0.003). For patients beyond BCLC stage B, between-group outcomes were similar. Other UGIB, non-bleeding liver decompensation and AEs did not differ between groups. A competing risk regression model confirmed the prognostic value of EVL. CONCLUSION: EVL is superior to PPL in preventing initial EVB in patients with HCC. The benefits of EVL on EVB and OS may be limited to patients with BCLC stage A/B and not to those with BCLC stage C/D. TRIAL REGISTRATION NUMBER: NCT01970748.

Molecular basis for dual functions in pilus assembly modulated by the lid of a pilus-specific sortase.

In Gram-positive bacteria, the biphasic assembly of pili begins with the covalent polymerization of distinct pilins catalyzed by a pilus-specific sortase, followed by anchoring of the resulting polymers to the cell wall mediated by the housekeeping sortase. Uniquely, in Actinomyces oris , the SrtC2 sortase not only polymerizes FimA pilins to assemble type 2 fimbriae, but it can also act as the anchoring sortase, which joins both FimA polymers and SrtC1-catalyzed FimP polymers (type 1 fimbriae) to peptidoglycan when the housekeeping sortase SrtA is inactive. To date, the structure-function determinants governing the unique substrate specificity and dual enzymatic activity of SrtC2 have not been illuminated. Here, we present the crystal structure of SrtC2 solved to 2.10-Å resolution. SrtC2 harbors a canonical sortase fold and a lid typical for class C sortases and additional features specific to SrtC2. Structural comparisons of SrtC2 and SrtC1 reveal that the extended lid of SrtC2 modulates its dual activity. Specifically, we demonstrate that the polymerizing activity of SrtC2 is unaffected by alanine-substitution, partial deletion, and replacement of the SrtC2 lid with the SrtC1 lid. Strikingly, pilus incorporation of the tip adhesin CafA is significantly reduced by these mutations, leading to compromised polymicrobial interactions that require CafA. In a srtA mutant, the partial deletion of the SrtC2 lid reduces surface anchoring of FimP polymers, and the lid-swapping mutation enhances this process, while both mutations diminish surface anchoring of FimA pili. Evidently, the extended lid of SrtC2 enables the enzyme the cell wall-anchoring activity in a substrate-selective fashion.

The Basal and Major Pilins in the Corynebacterium diphtheriae SpaA Pilus Adopt Similar Structures that Competitively React with the Pilin Polymerase.

Many species of pathogenic gram-positive bacteria display covalently crosslinked protein polymers (called pili or fimbriae) that mediate microbial adhesion to host tissues. These structures are assembled by pilus-specific sortase enzymes that join the pilin components together via lysine-isopeptide bonds. The archetypal SpaA pilus from Corynebacterium diphtheriae is built by the Cd SrtA pilus-specific sortase, which crosslinks lysine residues within the SpaA and SpaB pilins to build the shaft and base of the pilus, respectively. Here, we show that Cd SrtA crosslinks SpaB to SpaA via a K139(SpaB)-T494(SpaA) lysine-isopeptide bond. Despite sharing only limited sequence homology, an NMR structure of SpaB reveals striking similarities with the N-terminal domain of SpaA ( N SpaA) that is also crosslinked by Cd SrtA. In particular, both pilins contain similarly positioned reactive lysine residues and adjacent disordered AB loops that are predicted to be involved in the recently proposed "latch" mechanism of isopeptide bond formation. Competition experiments using an inactive SpaB variant and additional NMR studies suggest that SpaB terminates SpaA polymerization by outcompeting N SpaA for access to a shared thioester enzyme-substrate reaction intermediate.

A cryptic oxidoreductase safeguards oxidative protein folding in Corynebacterium diphtheriae.

In many gram-positive Actinobacteria, including Actinomyces oris and Corynebacterium matruchotii, the conserved thiol-disulfide oxidoreductase MdbA that catalyzes oxidative folding of exported proteins is essential for bacterial viability by an unidentified mechanism. Intriguingly, in Corynebacterium diphtheriae, the deletion of mdbA blocks cell growth only at 37 °C but not at 30 °C, suggesting the presence of alternative oxidoreductase enzyme(s). By isolating spontaneous thermotolerant revertants of the mdbA mutant at 37 °C, we obtained genetic suppressors, all mapped to a single T-to-G mutation within the promoter region of tsdA, causing its elevated expression. Strikingly, increased expression of tsdA-via suppressor mutations or a constitutive promoter-rescues the pilus assembly and toxin production defects of this mutant, hence compensating for the loss of mdbA. Structural, genetic, and biochemical analyses demonstrated TsdA is a membrane-tethered thiol-disulfide oxidoreductase with a conserved CxxC motif that can substitute for MdbA in mediating oxidative folding of pilin and toxin substrates. Together with our observation that tsdA expression is upregulated at nonpermissive temperature (40 °C) in wild-type cells, we posit that TsdA has evolved as a compensatory thiol-disulfide oxidoreductase that safeguards oxidative protein folding in C. diphtheriae against thermal stress.

Genetic Determinants of Hydrogen Sulfide Biosynthesis in Fusobacterium nucleatum Are Required for Bacterial Fitness, Antibiotic Sensitivity, and Virulence.

The Gram-negative anaerobe Fusobacterium nucleatum is a major producer of hydrogen sulfide (H2S), a volatile sulfur compound that causes halitosis. Here, we dissected the genetic determinants of H2S production and its role in bacterial fitness and virulence in this important member of the oral microbiome. F. nucleatum possesses four enzymes, CysK1, CysK2, Hly, and MegL, that presumably metabolize l-cysteine to H2S, and CysK1 was previously shown to account for most H2S production in vitro, based on correlations of enzymatic activities with gene expression at mid-log phase. Our molecular studies showed that cysK1 and megL were highly expressed at the late exponential growth phase, concomitant with high-level H2S production, while the expression levels of the other genes remained substantially lower during all growth phases. Although the genetic deletion of cysK1 without supplementation with a CysK1-catalyzed product, lanthionine, caused cell death, the conditional ΔcysK1 mutant and a mutant lacking hly were highly proficient in H2S production. In contrast, a mutant devoid of megL showed drastically reduced H2S production, and a cysK2 mutant showed only minor deficiencies. Intriguingly, the exposure of these mutants to various antibiotics revealed that only the megL mutant displayed altered susceptibility compared to the parental strain: partial sensitivity to nalidixic acid and resistance to kanamycin. Most significantly, the megL mutant was attenuated in virulence in a mouse model of preterm birth, with considerable defects in the spread to amniotic fluid and the colonization of the placenta and fetus. Evidently, the l-methionine γ-lyase MegL is a major H2S-producing enzyme in fusobacterial cells that significantly contributes to fusobacterial virulence and antibiotic susceptibility. IMPORTANCE Fusobacterium nucleatum is a key commensal anaerobe of the human oral cavity that plays a significant role in oral biofilm development and contributes to additional pathologies at extraoral sites, such as promoting preterm birth and colorectal cancer. Although F. nucleatum is known as a major producer of hydrogen sulfide (H2S), its genetic determinants and physiological functions are not well understood. By a combination of bacterial genetics, biochemical methods, and in vivo models of infection, here, we demonstrate that the l-methionine γ-lyase MegL not only is a major H2S-producing enzyme of F. nucleatum but also significantly contributes to the antibiotic susceptibility and virulence of this organism.

The Resistance Mechanisms and Clinical Impact of Resistance to the Third Generation Cephalosporins in Species of Enterobacter cloacae Complex in Taiwan.

Enterobacter cloacae complex (ECC) is ubiquitous in the environment and is an important pathogen causing nosocomial infections. Because routine methods used in clinical laboratories cannot identify species within ECC, the clinical significance of each species within ECC is less known. We applied hsp60 gene sequencing to identify the species/clusters of ECC and detected ß-lactamase genes and class 1 integrons with PCR for 184 clinical ECC isolates in Taiwan from 2013 to 2014 to investigate the clinical impact of species within ECC. The four most common clusters were E. hormaechei subsp. steigerwaltii (cluster VIII) (29.9%), E. hormaechei subsp. oharae (cluster VI) (20.1%), E. cloacae subsp. cloacae (cluster XI) (12%), and E. kobei (cluster II) (10.3%). E. hormaechei, which consisted of four clusters (clusters III, VI, VII, and VIII), is the predominant species and accounted for 57.1% of the isolates. The ceftazidime resistance rate was 27.2%, and the ceftriaxone resistance rate was 29.3%. Resistance to third generation cephalosporin was associated with a higher 30-day mortality rate. In total, 5 (2.7%), 24 (13.0%), and 1 (0.5%) isolates carried ESBL, AmpC, and carbapenemase genes, respectively. Class 1 integrons were present in 24.5% of the isolates, and most of the cassettes pertain to antibiotic resistance. Resistance to third generation cephalosporins, multidrug resistance, and class 1 integrons were significantly more in E. hormaechei (clusters III, VI, VII, and VIII) than in the other species. The 30-day mortality rate and 100-day mortality did not differ significantly between patients with E. hormaechei and those with infections with the other species. In conclusion, the distribution of third generation cephalosporin resistance, multidrug resistance, and class 1 integrons were uneven among Enterobacter species. The resistance to third generation cephalosporins possessed significant impact on patient outcome.

A conserved signal-peptidase antagonist modulates membrane homeostasis of actinobacterial sortase critical for surface morphogenesis.

Most Actinobacteria encode a small transmembrane protein, whose gene lies immediately downstream of the housekeeping sortase coding for a transpeptidase that anchors many extracellular proteins to the Gram-positive bacterial cell wall. Here, we uncover the hitherto unknown function of this class of conserved proteins, which we name SafA, as a topological modulator of sortase in the oral Actinobacterium Actinomyces oris. Genetic deletion of safA induces cleavage and excretion of the otherwise predominantly membrane-bound SrtA in wild-type cells. Strikingly, the safA mutant, although viable, exhibits severe abnormalities in cell morphology, pilus assembly, surface protein localization, and polymicrobial interactions-the phenotypes that are mirrored by srtA depletion. The pleiotropic defect of the safA mutant is rescued by ectopic expression of safA from not only A. oris, but also Corynebacterium diphtheriae or Corynebacterium matruchotii. Importantly, the SrtA N terminus harbors a tripartite-domain feature typical of a bacterial signal peptide, including a cleavage motif AXA, mutations in which prevent SrtA cleavage mediated by the signal peptidase LepB2. Bacterial two-hybrid analysis demonstrates that SafA and SrtA directly interact. This interaction involves a conserved motif FPW within the exoplasmic face of SafA, since mutations of this motif abrogate SafA-SrtA interaction and induce SrtA cleavage and excretion as observed in the safA mutant. Evidently, SafA is a membrane-imbedded antagonist of signal peptidase that safeguards and maintains membrane homeostasis of the housekeeping sortase SrtA, a central player of cell surface assembly.

The risk of variceal bleeding during endoscopic retrograde cholangiopancreatography.

BACKGROUND: Endoscopic retrograde cholangiopancreatography (ERCP) is a widely performed procedure. However, the risk of variceal bleeding during ERCP has rarely been assessed. This study aims to evaluate the risk of variceal bleeding in patients with esophageal varices (EV) undergoing ERCP. METHODS: From October 2010 to November 2017, the study retrospectively enrolled 75 cirrhotic patients who received elective ERCP. The patient's risk of gastrointestinal (GI) and variceal bleeding and other procedure-related adverse events within 30 days of ERCP were evaluated. RESULTS: Among the 75 patients, 45 patients (60.0%) had EV. Most of the patients were males (65.3%), and there were high rates of viral hepatitis B-related cirrhosis (36.0%), Child-Pugh B (49.3%), and an indication of choledocholithiasis (40.0%). Thirty-three of 45 (73.3%) patients had high-risk EV, and nine (20.0%) patients had concomitant gastric varices. There was no esophageal variceal bleeding; however, one patient had gastric variceal bleeding after ERCP. Nonvariceal significant GI bleeding occurred in three patients with EV and one without EV ( p = 0.529). Post-ERCP pancreatitis occurred in three patients with EV and five without EV ( p = 0.169). No perforation or procedure-associated mortality was noted. CONCLUSION: The risk of esophageal variceal bleeding within 30 days of ERCP is neglectable, except for a patient who suffered from gastric variceal bleeding. Other complications, such as nonvariceal bleeding and pancreatitis, are also no higher in patients with EV. Therefore, ERCP is generally a safe procedure for a patient with high-risk esophageal varices.

Topical application of Porphyromonas gingivalis into the gingival pocket in mice leads to chronic­active infection, periodontitis and systemic inflammation.

Porphyromonas gingivalis (Pg), one of the 'red­complex' perio­pathogens known to play a critical role in the development of periodontitis, has been used in various animal models to mimic human bacteria­induced periodontitis. In order to achieve a more realistic animal model of human Pg infection, the present study investigated whether repeated small­volume topical applications of Pg directly into the gingival pocket can induce local infection, including periodontitis and systemic vascular inflammation in wild­type mice. Freshly cultured Pg was topically applied directly into the gingival pocket of the second molars for 5 weeks (3 times/week). After the final application, the mice were left in cages for 4 or 8 weeks and sacrificed. The status of Pg colony formation in the pocket, gingival inflammation, alveolar bone loss, the expression levels of pro­inflammatory cytokines in the serum and aorta, the presence of anti­Pg lipopolysaccharide (LPS) and gingipain (Kpg and RgpB) antibodies in the serum, as well as the accumulation of Pg LPS and gingipain aggregates in the gingiva and arterial wall were evaluated. The topical application of Pg into the gingival pocket induced the following local and systemic pathohistological changes in mice when examined at 4 or 8 weeks after the final topical Pg application: Pg colonization in the majority of gingival pockets; increased gingival pocket depths; gingival inflammation indicated by the increased expression of TNF­α, IL­6 and IL­1ß; significant loss of alveolar bone at the sites of topical Pg application; and increased levels of pro­inflammatory cytokines, such as TNF­α, IL­1ß, IL­17, IL­13, KC and IFN­Î³ in the serum in comparison to those from mice receiving PBS. In addition, the Pg application/colonization model induced anti­Pg LPS and gingipain antibodies in serum, as well as the accumulation of Pg LPS and gingipain aggregates in the gingivae and arterial walls. To the best of our knowledge, this mouse model represents the first example of creating a more sustained local infection in the gingival tissues of wild­type mice and may prove to be useful for the investigation of the more natural and complete pathogenesis of the bacteria in the development of local oral and systemic diseases, such as atherosclerosis. It may also be useful for the determination of a treatment/prevention/efficacy model associated with Pg­induced colonization periodontitis in mice.

Rapid Characterization of Bacterial Lipids with Ambient Ionization Mass Spectrometry for Species Differentiation.

Ambient ionization mass spectrometry (AIMS) is both labor and time saving and has been proven to be useful for the rapid delineation of trace organic and biological compounds with minimal sample pretreatment. Herein, an analytical platform of probe sampling combined with a thermal desorption-electrospray ionization/mass spectrometry (TD-ESI/MS) and multivariate statistical analysis was developed to rapidly differentiate bacterial species based on the differences in their lipid profiles. For comparison, protein fingerprinting was also performed with matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) to distinguish these bacterial species. Ten bacterial species, including five Gram-negative and five Gram-positive bacteria, were cultured, and the lipids in the colonies were characterized with TD-ESI/MS. As sample pretreatment was unnecessary, the analysis of the lipids in a bacterial colony growing on a Petri dish was completed within 1 min. The TD-ESI/MS results were further performed by principal component analysis (PCA) and hierarchical cluster analysis (HCA) to assist the classification of the bacteria, and a low relative standard deviation (5.2%) of the total ion current was obtained from repeated analyses of the lipids in a single bacterial colony. The PCA and HCA results indicated that different bacterial species were successfully distinguished by the differences in their lipid profiles as validated by the differences in their protein profiles recorded from the MALDI-TOF analysis. In addition, real-time monitoring of the changes in the specific lipids of a colony with growth time was also achieved with probe sampling and TD-ESI/MS. The developed analytical platform is promising as a useful diagnostic tool by which to rapidly distinguish bacterial species in clinical practice.

The Fused Methionine Sulfoxide Reductase MsrAB Promotes Oxidative Stress Defense and Bacterial Virulence in Fusobacterium nucleatum.

Fusobacterium nucleatum, an anaerobic Gram-negative bacterium frequently found in the human oral cavity and some extra-oral sites, is implicated in several important diseases: periodontitis, adverse pregnancy outcomes, and colorectal cancer. To date, how this obligate anaerobe copes with oxidative stress and host immunity within multiple human tissues remains unknown. Here, we uncovered a critical role in this process of a multigene locus encoding a single, fused methionine sulfoxide reductase (MsrAB), a two-component signal transduction system (ModRS), and thioredoxin (Trx)- and cytochrome c (CcdA)-like proteins, which are induced when fusobacterial cells are exposed to hydrogen peroxide. Comparative transcriptome analysis revealed that the response regulator ModR regulates a large regulon that includes trx, ccdA, and many metabolic genes. Significantly, specific mutants of the msrAB locus, including msrAB, are sensitive to reactive oxygen species and defective in adherence/invasion of colorectal epithelial cells. Strikingly, the msrAB mutant is also defective in survival in macrophages, and it is severely attenuated in virulence in a mouse model of preterm birth, consistent with its failure to spread to the amniotic fluid and colonize the placenta. Clearly, the MsrAB system regulated by the two-component system ModRS represents a major oxidative stress defense pathway that protects fusobacteria against oxidative damage in immune cells and confers virulence by enabling attachment and invasion of multiple target tissues. IMPORTANCE F. nucleatum colonizes various human tissues, including oral cavity, placenta, and colon. How this obligate anaerobe withstands oxidative stress in host immune cells has not been described. We report here that F. nucleatum possesses a five-gene locus encoding a fused methionine sulfoxide reductase (MsrAB), a two-component signal transduction system (ModRS), and thioredoxin- and cytochrome c-like proteins. Regulated by ModRS, MsrAB is essential for resistance to reactive oxygen species, adherence/invasion of colorectal epithelial cells, and survival in macrophage. Unable to colonize placenta and spread to amniotic fluid, the msrAB mutant failed to induce preterm birth in a murine model.

A cell wall-anchored glycoprotein confers resistance to cation stress in Actinomyces oris biofilms.

Actinomyces oris plays an important role in oral biofilm development. Like many gram-positive bacteria, A. oris produces a sizable number of surface proteins that are anchored to bacterial peptidoglycan by a conserved transpeptidase named the housekeeping sortase SrtA; however, the biological role of many A. oris surface proteins in biofilm formation is largely unknown. Here, we report that the glycoprotein GspA-a genetic suppressor of srtA deletion lethality-not only promotes biofilm formation but also maintains cell membrane integrity under cation stress. In comparison to wild-type cells, under elevated concentrations of mono- and divalent cations the formation of mono- and multi-species biofilms by mutant cells devoid of gspA was significantly diminished, although planktonic growth of both cell types in the presence of cations was indistinguishable. Because gspA overexpression is lethal to cells lacking gspA and srtA, we performed a genetic screen to identify GspA determinants involving cell viability. DNA sequencing and biochemical characterizations of viable clones revealed that mutations of two critical cysteine residues and a serine residue severely affected GspA glycosylation and biofilm formation. Furthermore, mutant cells lacking gspA were markedly sensitive to sodium dodecyl sulfate, a detergent that solubilizes the cytoplasmic membranes, suggesting the cell envelope of the gspA mutant was altered. Consistent with this observation, the gspA mutant exhibited increased membrane permeability, independent of GspA glycosylation, compared to the wild-type strain. Altogether, the results support the notion that the cell wall-anchored glycoprotein GspA provides a defense mechanism against cation stress in biofilm development promoted by A. oris.

Molecular Epidemiology, Risk Factors and Clinical Outcomes of Carbapenem-Nonsusceptible Enterobacter cloacae Complex Infections in a Taiwan University Hospital.

The genus Enterobacter is a member of the ESKAPE group, which contains the major resistant bacterial pathogens. Enterobacter cloacae complex (ECC) has emerged as a clinically significant cause of a wide variety of nosocomial infections. Carbapenem-nonsusceptible Enterobacter cloacae complex (CnsECC) has become an emerging threat to public health but there is still a lack of comprehensive molecular and clinical epidemiological analysis. A total of 157 CnsECC isolates were recovered during October 2011 to August 2017. hsp60 gene sequencing and pulsed-field gel electrophoresis (PFGE) were applied to discriminate the species, genetic clusters and clonal relatedness. All the isolates were subjected to polymerase chain reaction (PCR) analysis for carbapenemase, AmpC-type ß-lactamase, and extended spectrum ß-lactamase (ESBL) genes. Clinical data were collected on all patients for comparing clinical risks and outcomes between patients with carbapenemase-producing (CP)-CnsECC compared with non-CP-CnsECC infection. The most commonly identified species was E. hormaechei subsp. hoffmannii (47.1%), followed by E. hormaechei subsp. steigerwaltii (24.8%). Different species of CnsECC isolates showed heterogeneity in resistance patterns to piperacillin/tazobactam, cefepime and levofloxacin. In the present study, we observed that E. hormaechei subsp. hoffmannii was characterized with higher cefepime and levofloxacin resistance rate but lower piperacillin/tazobactam resistance rate relative to other species of CnsECC. CP-CnsECC comprised 41.1% (65 isolates) and all of these isolates carried IMP-8. In this study, 98% of patients had antimicrobial therapy prior to culture, with a total of 57/150 (38%) patients being exposed to carbapenems. Chronic pulmonary disease (OR: 2.51, 95% CI: 1.25-5.06), received ventilator support (OR: 5.54, 95% CI: 2.25-12.03), steroid exposure (OR: 3.88, 95% CI: 1.91-7.88) and carbapenems exposure (OR: 2.17, 95% CI: 1.10-4.25) were considered risk factors associated with CP-CnsECC infection. The results suggest that CP-CnsECC are associated with poorer outcomes including in-hospital mortality, 30-day mortality and 100-day mortality. Our study provides insights into the epidemic potential of IMP-8-producing E. cloacae for healthcare-associated infections and underscores the importance of understanding underlying resistance mechanisms of CnsECC to direct antibiotic treatment decisions.

SARS-CoV-2 vaccination in patients with inflammatory bowel disease: A systemic review and meta-analysis.

BACKGROUND: In the coronavirus disease 2019 (COVID-19) pandemic, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) vaccination has been effective in preventing COVID-19 infections and related mortality. The SARS-CoV-2 vaccination was also recommended by the international society for patients with inflammatory bowel disease (IBD). However, IBD patients were not recruited in prospective randomized clinical vaccine studies. To evaluate the efficacy and safety of SARS-CoV-2 vaccination in IBD patients, we conducted this systemic review and meta-analysis. METHODS: We systematically searched PubMed, Medline, and the Cochrane Library for studies published between January 1, 2019, and September 9, 2021. Studies written in English reported the efficacy, seroconversion (anti-SARS-CoV-2 anti-spike (S) antibody titer beyond the threshold) rate, and adverse events after the SARS-CoV-2 vaccination in IBD patients. We extracted the author, date, study design, country, types of SARS-CoV-2 vaccination, number of IBD patients receiving SARS-CoV-2 vaccinations, and study outcomes. Published data from the enrolled studies were pooled to determine effect estimates. The study protocol was registered in PROSPERO (CRD42021264993). RESULTS: We analyzed findings from 27 454 IBD patients who received SARS-CoV-2 vaccinations in 11 studies that met the inclusion criteria. The post-SARS-CoV-2 vaccination COVID-19 infection rate was comparable between the IBD patients and non-IBD patients (odds ratio [OR], 1.28 [95% CI, 0.96-1.71]) and higher in nonvaccinated IBD patients compared with vaccinated IBD patients (OR, 8.63 [95% CI, 5.44-13.37]). The adverse event rate, severe adverse events, and mortality after the SARS-CoV-2 vaccination were 69%, 3%, and 0%, respectively. CONCLUSION: The SARS-CoV-2 vaccine is effective and tolerated in preventing COVID-19 infections in IBD patients. Over 98% of patients had seroconversion after receiving all doses of the SARS-CoV-2 vaccination, and the influence of biologics on vaccination was limited. The SARS-CoV-2 vaccination is recommended for IBD patients.

Genetic and molecular determinants of polymicrobial interactions in Fusobacterium nucleatum.

A gram-negative colonizer of the oral cavity, Fusobacterium nucleatum not only interacts with many pathogens in the oral microbiome but also has the ability to spread to extraoral sites including placenta and amniotic fluid, promoting preterm birth. To date, however, the molecular mechanism of interspecies interactions-termed coaggregation-by F. nucleatum and how coaggregation affects bacterial virulence remain poorly defined. Here, we employed genome-wide transposon mutagenesis to uncover fusobacterial coaggregation factors, revealing the intertwined function of a two-component signal transduction system (TCS), named CarRS, and a lysine metabolic pathway in regulating the critical coaggregation factor RadD. Transcriptome analysis shows that CarR modulates a large regulon including radD and lysine metabolic genes, such as kamA and kamD, the expression of which are highly up-regulated in the ΔcarR mutant. Significantly, the native culture medium of ΔkamA or ΔkamD mutants builds up abundant amounts of free lysine, which blocks fusobacterial coaggregation with streptococci. Our demonstration that lysine-conjugated beads trap RadD from the membrane lysates suggests that lysine utilizes RadD as its receptor to act as a metabolic inhibitor of coaggregation. Lastly, using a mouse model of preterm birth, we show that fusobacterial virulence is significantly attenuated with the ΔkamA and ΔcarR mutants, in contrast to the enhanced virulence phenotype observed upon diminishing RadD (ΔradD or ΔcarS mutant). Evidently, F. nucleatum employs the TCS CarRS and environmental lysine to modulate RadD-mediated interspecies interaction, virulence, and nutrient acquisition to thrive in the adverse environment of oral biofilms and extraoral sites.

Sortase-assembled pili in Corynebacterium diphtheriae are built using a latch mechanism.

Gram-positive bacteria assemble pili (fimbriae) on their surfaces to adhere to host tissues and to promote polymicrobial interactions. These hair-like structures, although very thin (1 to 5 nm), exhibit impressive tensile strengths because their protein components (pilins) are covalently crosslinked together via lysine-isopeptide bonds by pilus-specific sortase enzymes. While atomic structures of isolated pilins have been determined, how they are joined together by sortases and how these interpilin crosslinks stabilize pilus structure are poorly understood. Using a reconstituted pilus assembly system and hybrid structural biology methods, we elucidated the solution structure and dynamics of the crosslinked interface that is repeated to build the prototypical SpaA pilus from Corynebacterium diphtheriae We show that sortase-catalyzed introduction of a K190-T494 isopeptide bond between adjacent SpaA pilins causes them to form a rigid interface in which the LPLTG sorting signal is inserted into a large binding groove. Cellular and quantitative kinetic measurements of the crosslinking reaction shed light onto the mechanism of pilus biogenesis. We propose that the pilus-specific sortase in C. diphtheriae uses a latch mechanism to select K190 on SpaA for crosslinking in which the sorting signal is partially transferred from the enzyme to a binding groove in SpaA in order to facilitate catalysis. This process is facilitated by a conserved loop in SpaA, which after crosslinking forms a stabilizing latch that covers the K190-T494 isopeptide bond. General features of the structure and sortase-catalyzed assembly mechanism of the SpaA pilus are likely conserved in Gram-positive bacteria.

Ribonuclease J-Mediated mRNA Turnover Modulates Cell Shape, Metabolism and Virulence in Corynebacterium diphtheriae.

Controlled RNA degradation is a crucial process in bacterial cell biology for maintaining proper transcriptome homeostasis and adaptation to changing environments. mRNA turnover in many Gram-positive bacteria involves a specialized ribonuclease called RNase J (RnJ). To date, however, nothing is known about this process in the diphtheria-causative pathogen Corynebacterium diphtheriae, nor is known the identity of this ribonuclease in this organism. Here, we report that C. diphtheriae DIP1463 encodes a predicted RnJ homolog, comprised of a conserved N-terminal ß-lactamase domain, followed by ß-CASP and C-terminal domains. A recombinant protein encompassing the ß-lactamase domain alone displays 5'-exoribonuclease activity, which is abolished by alanine-substitution of the conserved catalytic residues His186 and His188. Intriguingly, deletion of DIP1463/rnj in C. diphtheriae reduces bacterial growth and generates cell shape abnormality with markedly augmented cell width. Comparative RNA-seq analysis revealed that RnJ controls a large regulon encoding many factors predicted to be involved in biosynthesis, regulation, transport, and iron acquisition. One upregulated gene in the ∆rnj mutant is ftsH, coding for a membrane protease (FtsH) involved in cell division, whose overexpression in the wild-type strain also caused cell-width augmentation. Critically, the ∆rnj mutant is severely attenuated in virulence in a Caenorhabditis elegans model of infection, while the FtsH-overexpressing and toxin-less strains exhibit full virulence as the wild-type strain. Evidently, RNase J is a key ribonuclease in C. diphtheriae that post-transcriptionally influences the expression of numerous factors vital to corynebacterial cell physiology and virulence. Our findings have significant implications for basic biological processes and mechanisms of corynebacterial pathogenesis.

Prophylactic clipping after endoscopic mucosal resection of large nonpedunculated colorectal lesions: A meta-analysis.

BACKGROUND AND AIM: It is not clear whether prophylactic clipping after endoscopic mucosal resection (EMR) of large nonpedunculated colorectal lesions (LNPCLs) prevents delayed bleeding (DB). We aimed to conduct a meta-analysis to clarify the efficacy of prophylactic clipping in prevention of DB following EMR of LNPCLs. METHODS: We searched PubMed, EMBASE, Web of Science, ScienceDirect, Cochrane Library databases, and ClinicalTrials.gov for studies that compared clipping versus (vs) nonclipping in prevention of DB following EMR of LNPCLs. Pooled odds ratio (OR) was determined using a random effects model. The pooled ORs of DB, perforation, and post-polypectomy syndrome in the clipping group compared with the nonclipping group comprised the outcomes. Subgroup analyses based on study design, polyp location, and completeness of wound closure were performed. RESULTS: Five studies with a total of 3112 LNPCLs were extracted. Prophylactic clipping reduced the risk of DB compared with nonclipping (3.3% vs 6.2%, OR: 0.494, P = 0.002) following EMR of LNPCLs. In subgroup analysis, prophylactic clipping reduced DB of LNPCLs at proximal location (3.8% vs 9.8%, P = 0.029), but not of them at distal location (P = 0.830). Complete wound closure showed superior efficacy to prevent DB compared with partial closure (2.0% vs 5.4%, P = 0.004). No benefit of clipping for preventing perforation or post-polypectomy syndrome was observed (P = 0.301 and 0.988, respectively). CONCLUSIONS: Prophylactic clipping can reduce DB following EMR of LNPCLs at proximal location. Besides, complete wound closure showed superior efficacy to prevent DB compared with partial closure. Further cost analyses should be conducted to implement the most cost-effective strategies.