Phage transcriptional regulator X (PtrX)-mediated augmentation of toxin production and virulence in Clostridioides difficile strain R20291

Clostridioides difficile is a Gram-positive, anaerobic, and spore-forming bacterial member of the human gut microbiome. The primary virulence factors of C. difficile are toxin A and toxin B. These toxins damage the cell cytoskeleton and cause various diseases, from diarrhea to severe pseudomembranous colitis. Evidence suggests that bacteriophages can regulate the expression of the pathogenicity locus (PaLoc) genes of C. difficile. We previously demonstrated that the genome of the C. difficile RT027 strain NCKUH-21 contains a prophage-like DNA sequence, which was found to be markedly similar to that of the φCD38-2 phage. In the present study, we investigated the mechanisms underlying the φNCKUH-21-mediated regulation of the pathogenicity and the PaLoc genes expression in the lysogenized C. difficile strain R20291. The carriage of φNCKUH-21 in R20291 cells substantially enhanced toxin production, bacterial motility, biofilm formation, and spore germination in vitro. Subsequent mouse studies revealed that the lysogenized R20291 strain caused a more severe infection than the wild-type strain. We screened three φNCKUH-21 genes encoding DNA-binding proteins to check their effects on PaLoc genes expression. The overexpression of NCKUH-21_03890, annotated as a transcriptional regulator (phage transcriptional regulator X, PtrX), considerably enhanced toxin production, biofilm formation, and bacterial motility of R20291. Transcriptome analysis further confirmed that the overexpression of ptrX led to the upregulation of the expression of toxin genes, flagellar genes, and csrA. In the ptrX-overexpressing R20291 strain, PtrX influenced the expression of flagellar genes and the sigma factor gene sigD, possibly through an increased flagellar phase ON configuration ratio.

Hypervirulent Clostridioides difficile RT078 lineage isolates from the river: A potential reservoir for environmental transmission

This is the first report to discover Clostridiodes difficile (C. difficile) ribotype RT126 and RT598 (both ribotypes belong to RT078-lineage) in a river water system in southern Taiwan. Fluoroquinolone resistance was also found. The connection between clinical isolates and those from the environment needs further investigation.

Uremic Toxin-Producing Bacteroides Species Prevail in the Gut Microbiota of Taiwanese CKD Patients: An Analysis Using the New Taiwan Microbiome Baseline

Rationale and Objective

Gut microbiota have been targeted by alternative therapies for non-communicable diseases. We examined the gut microbiota of a healthy Taiwanese population, identified various bacterial drivers in different demographics, and compared them with dialysis patients to associate kidney disease progression with changes in gut microbiota.

Study Design

This was a cross-sectional cohort study.

Settings and Participants

Fecal samples were obtained from 119 healthy Taiwanese volunteers, and 16S rRNA sequencing was done on the V3-V4 regions to identify the bacterial enterotypes. Twenty-six samples from the above cohort were compared with fecal samples from 22 peritoneal dialysis and 16 hemodialysis patients to identify species-level bacterial biomarkers in the dysbiotic gut of chronic kidney disease (CKD) patients.

Results

Specific bacterial species were identified pertaining to different demographics such as gender, age, BMI, physical activity, and sleeping habits. Dialysis patients had a significant difference in gut microbiome composition compared to healthy controls. The most abundant genus identified in CKD patients was Bacteroides, and at the species level hemodialysis patients showed significant abundance in B. ovatus, B. caccae, B. uniformis, and peritoneal dialysis patients showed higher abundance in Blautia producta (p ≤ 0.05) than the control group. Pathways pertaining to the production of uremic toxins were enriched in CKD patients. The abundance of the bacterial species depended on the type of dialysis treatment.

Conclusion

This study characterizes the healthy gut microbiome of a Taiwanese population in terms of various demographics. In a case-control examination, the results showed the alteration in gut microbiota in CKD patients corresponding to different dialysis treatments. Also, this study identified the bacterial species abundant in CKD patients and their possible role in complicating the patients’ condition.

Clostridium butyricum therapy for mild-moderate Clostridioides difficile infection and the impact of diabetes mellitus

The therapeutic effect of Clostridium butyricum for adults with Clostridioides difficile infection (CDI) was investigated. A retrospective study was conducted in medical wards of Tainan Hospital, Ministry of Health and Welfare, between January 2013 and April 2020. The disease severity of CDI was scored based on the Clinical Practice Guidelines of the IDSA/SHEA. Treatment success was defined as the resolution of diarrhea within six days of a therapeutic intervention without the need to modify the therapeutic regimen. In total, 241 patients developed CDI during hospitalization in the study period. The treatment success rates for the 99 patients with mild-moderate CDI among them were as follows: metronidazole, 69.4%; C. butyricum, 68.2%; metronidazole plus C. butyricum, 66.7%; and oral vancomycin, 66.7% (p=1.00). Patients with treatment success were less likely to have diabetes mellitus than those with treatment failure (38.2% vs. 61.3%, p=0.05). Patients treated with C. butyricum alone or in combination with metronidazole had shorter durations of diarrhea than those treated with metronidazole alone (3.1 ± 2.0 days or 3.5 ± 2.4 days vs. 4.2 ± 3.5 days; p=0.43 or 0.71), although the differences were not statistically significant. In conclusion, the treatment success rate of C. butyricum alone or in combination with metronidazole for patients with CDI was non inferior to that of metronidazole alone. The presence of diabetes mellitus in affected individuals is a risk factor for treatment failure.

Clostridioides difficile spores stimulate inflammatory cytokine responses and induce cytotoxicity in macrophages

Clostridioides difficile is a gram-positive, spore-forming anaerobic bacterium, and the leading cause of antibiotic-associated diarrhea worldwide. During C. difficile infection, spores germinate in the presence of bile acids into vegetative cells that subsequently colonize the large intestine and produce toxins. In this study, we demonstrated that C. difficile spores can universally adhere to, and be phagocytosed by, murine macrophages. Only spores from toxigenic strains were able to significantly stimulate the production of inflammatory cytokines by macrophages and subsequently induce significant cytotoxicity. Spores from the isogenic TcdA and TcdB double mutant induced significantly lower inflammatory cytokines and cytotoxicity in macrophages, and these activities were restored by pre-exposure of the spores to either toxins. These findings suggest that during sporulation, spores might be coated with C. difficile toxins from the environment, which could affect C. difficile pathogenesis in vivo.

Swimming Pool-Associated Vittaforma-Like Microsporidia Linked to Microsporidial Keratoconjunctivitis Outbreak, Taiwan

We analyzed 2 batches of environmental samples after a microsporidial keratoconjunctivitis outbreak in Taiwan. Results indicated a transmission route from a parking lot to a foot washing pool to a swimming pool and suggested that accumulation of mud in the foot washing pool during the rainy season might be a risk factor.

Functional analysis of Clostridium difficile sortase B reveals key residues for catalytic activity and substrate specificity

Most of Gram-positive bacteria anchor surface proteins to the peptidoglycan cell wall by sortase, a cysteine transpeptidase that targets proteins displaying a cell wall sorting signal. Unlike other bacteria, Clostridium difficile, the major human pathogen responsible for antibiotic-associated diarrhea, has only a single functional sortase (SrtB). Sortase's vital importance in bacterial virulence has been long recognized, and C. difficile sortase B (Cd-SrtB) has become an attractive therapeutic target for managing C. difficile infection. A better understanding of the molecular activity of Cd-SrtB may help spur the development of effective agents against C. difficile infection. In this study, using site-directed mutagenesis, biochemical and biophysical tools, LC-MS/MS, and crystallographic analyses, we identified key residues essential for Cd-SrtB catalysis and substrate recognition. To the best of our knowledge, we report the first evidence that a conserved serine residue near the active site participates in the catalytic activity of Cd-SrtB and also SrtB from Staphylococcus aureus The serine residue indispensable for SrtB activity may be involved in stabilizing a thioacyl-enzyme intermediate because it is neither a nucleophilic residue nor a substrate-interacting residue, based on the LC-MS/MS data and available structural models of SrtB-substrate complexes. Furthermore, we also demonstrated that residues 163-168 located on the β6/β7 loop of Cd-SrtB dominate specific recognition of the peptide substrate PPKTG. The results of this work reveal key residues with roles in catalysis and substrate specificity of Cd-SrtB.

The Transcriptional Regulator Lrp Contributes to Toxin Expression, Sporulation, and Swimming Motility in Clostridium difficile

Clostridium difficile is a Gram-positive, spore-forming bacterium, and major cause of nosocomial diarrhea. Related studies have identified numerous factors that influence virulence traits such as the production of the two primary toxins, toxin A (TcdA) and toxin B (TcdB), as well as sporulation, motility, and biofilm formation. However, multiple putative transcriptional regulators are reportedly encoded in the genome, and additional factors are likely involved in virulence regulation. Although the leucine-responsive regulatory protein (Lrp) has been studied extensively in Gram-negative bacteria, little is known about its function in Gram-positive bacteria, although homologs have been identified in the genome. This study revealed that disruption of the lone lrp homolog in C. difficile decelerated growth under nutrient-limiting conditions, increased TcdA and TcdB production. Lrp was also found to negatively regulate sporulation while positively regulate swimming motility in strain R20291, but not in strain 630. The C. difficile Lrp appeared to function through transcriptional repression or activation. In addition, the lrp mutant was relatively virulent in a mouse model of infection. The results of this study collectively demonstrated that Lrp has broad regulatory function in C. difficile toxin expression, sporulation, motility, and pathogenesis.

Micro-colonization of arsenic-resistant Staphylococcus sp. As-3 on arsenopyrite (FeAsS) drives arsenic mobilization under anoxic sub-surface mimicking conditions

We investigated the subsurface biomatrix of the most abundant As-mineral, arsenopyrite (FeAsS), and meticulously studied a potential biogenic arsenic mobilization phenomenon. An arsenic-resistant [up to 7.5 mM As(III) and 200 mM As(V)] and arsenate-reducing bacterial strain (Staphylococcus sp. As-3) was isolated from a sediment core sample taken from the Budai borehole, on the southwestern coast of Taiwan. Isolate As-3 could reduce 5 mM As(V) to 3.04 mM in 96 h, generating 1.6 mM As(III) under anoxic conditions. Isolate As-3, which adsorbed As(V) up to 19.02 mg g^-1 (cdw) and As(III) up to 0.46 mg g^-1 (cdw), demonstrated effective As-bioaccumulating ability, as corroborated by a TEM-EDS analysis. Under anaerobic batch conditions, isolate As-3 micro-colonies could grow on as well as interact with arsenopyrite (FeAsS), mobilizing arsenic into soluble phase as As(III) and As(V). Using synchrotron radiation-based FTIR micro-spectroscopy, various functional group signatures and critical chemical bonds enabling a direct interaction with arsenopyrite were underpinned, such as a potential P-OFe bond involved in facilitating bacteria-mineral interaction. Using atomic force microscopy, we analyzed the scattered bacterial cell arrangement and structure and measured various biomechanical properties of micro-colonized Staphylococcus sp. As-3 cells on arsenopyrite. We suggest that the release of organic acids from As-3 drives soluble arsenic release in the aqueous phase under anoxic conditions through oxidative dissolution. Furthermore, arsC-encoding putative cytoplasmic arsenic reductase sequencing and transcript characterization indicated that arsC plays a possible role in the reduction of moderately soluble As(V) to highly soluble toxic As(III) under anoxic conditions. Thus, we suggest that firmicutes such as Staphylococcus sp. As-3 may play an important role in microbially-mediated arsenic mobilization, leading to arsenic release in the sub-surface niche.

In vitro reconstitution of sortase-catalyzed pilus polymerization reveals structural elements involved in pilin cross-linking

Covalently cross-linked pilus polymers displayed on the cell surface of Gram-positive bacteria are assembled by class C sortase enzymes. These pilus-specific transpeptidases located on the bacterial membrane catalyze a two-step protein ligation reaction, first cleaving the LPXTG motif of one pilin protomer to form an acyl-enzyme intermediate and then joining the terminal Thr to the nucleophilic Lys residue residing within the pilin motif of another pilin protomer. To date, the determinants of class C enzymes that uniquely enable them to construct pili remain unknown. Here, informed by high-resolution crystal structures of corynebacterial pilus-specific sortase (SrtA) and utilizing a structural variant of the enzyme (SrtA2M), whose catalytic pocket has been unmasked by activating mutations, we successfully reconstituted in vitro polymerization of the cognate major pilin (SpaA). Mass spectrometry, electron microscopy, and biochemical experiments authenticated that SrtA2M synthesizes pilus fibers with correct Lys-Thr isopeptide bonds linking individual pilins via a thioacyl intermediate. Structural modeling of the SpaA-SrtA-SpaA polymerization intermediate depicts SrtA2M sandwiched between the N- and C-terminal domains of SpaA harboring the reactive pilin and LPXTG motifs, respectively. Remarkably, the model uncovered a conserved TP(Y/L)XIN(S/T)H signature sequence following the catalytic Cys, in which the alanine substitutions abrogated cross-linking activity but not cleavage of LPXTG. These insights and our evidence that SrtA2M can terminate pilus polymerization by joining the terminal pilin SpaB to SpaA and catalyze ligation of isolated SpaA domains in vitro provide a facile and versatile platform for protein engineering and bio-conjugation that has major implications for biotechnology.

Lauric Acid Is an Inhibitor of Clostridium difficile Growth in Vitro and Reduces Inflammation in a Mouse Infection Model

Clostridium difficile is a Gram-positive, spore-forming anaerobic human gastrointestinal pathogen. C. difficile infection (CDI) is a major health concern worldwide, with symptoms ranging from diarrhea to pseudomembranous colitis, toxic megacolon, sepsis, and death. CDI onset and progression are mostly caused by intestinal dysbiosis and exposure to C. difficile spores. Current treatment strategies include antibiotics; however, antibiotic use is often associated with high recurrence rates and an increased risk of antibiotic resistance. Medium-chain fatty acids (MCFAs) have been revealed to inhibit the growth of multiple human bacterial pathogens. Components of coconut oil, which include lauric acid, have been revealed to inhibit C. difficile growth in vitro. In this study, we demonstrated that lauric acid exhibits potent antimicrobial activities against multiple toxigenic C. difficile isolates in vitro. The inhibitory effect of lauric acid is partly due to reactive oxygen species (ROS) generation and cell membrane damage. The administration of lauric acid considerably reduced biofilm formation and preformed biofilms in a dose-dependent manner. Importantly, in a mouse infection model, lauric acid pretreatment reduced CDI symptoms and proinflammatory cytokine production. Our combined results suggest that the naturally occurring MCFA lauric acid is a novel C. difficile inhibitor and is useful in the development of an alternative or adjunctive treatment for CDI.

Comparative genomic analysis of Clostridium difficile ribotype 027 strains including the newly sequenced strain NCKUH-21 isolated from a patient in Taiwan

Background

Clostridium difficile is a Gram-positive anaerobe and the leading cause of antibiotic-associated diarrhea worldwide. The emergence of ribotype 027 (RT027) strains is associated with increased incidence of infection and mortality. To further understand the relationship between C. difficile NCKUH-21, a RT027 strain isolated from a patient in Taiwan, and other RT027 strains, we performed whole-genome shotgun sequencing on NCKUH-21 and comparative genomic analyses.

Results

The genome size, G+C content, and gene number for the NCKUH-21 strain were determined to be similar to those for other C. difficile strains. The core genome phylogeny indicated that the five RT027 strains R20291, CD196, NCKUH-21, BI1, and 2007855 formed a clade. A pathogenicity locus, tcdR-tcdB-tcdE-orf-tcdA-tcdC, was conserved in the genome. A genomic region highly similar to the Clostridium phage \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upvarphi$$\end{document}φCD38-2 was present in the NCKUH-21 strain but absent in the other RT027 strains and designated as the prophage \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upvarphi$$\end{document}φNCKUH-21. The prophage \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upvarphi$$\end{document}φNCKUH-21 genes were significantly higher in G+C content than the other genes in the NCKUH-21 genome, indicating that the prophage does not match the base composition of the host genome.

Conclusions

This is the first whole-genome analysis of a RT027 C. difficile strain isolated from Taiwan. Due to the high identity with \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upvarphi$$\end{document}φCD38-2, the prophage identified in the NCKUH-21 genome has the potential to regulate toxin production. These results provide important information for understanding the pathogenicity of RT027 C. difficile in Taiwan.

Electronic supplementary material

The online version of this article (10.1186/s13099-017-0219-4) contains supplementary material, which is available to authorized users.

Immunization with Recombinant TcdB-Encapsulated Nanocomplex Induces Protection against Clostridium difficile Challenge in a Mouse Model

Clostridium difficile is considered to be one of the major cause of infectious diarrhea in healthcare systems worldwide. Symptoms of C. difficile infection are caused largely by the production of two cytotoxins: toxin A (TcdA) and toxin B (TcdB). Vaccine development is considered desirable as it would decrease the mounting medical costs and mortality associated with C. difficile infections. Biodegradable nanoparticles composed of poly-γ-glutamic acid (γ-PGA) and chitosan have proven to be a safe and effective antigen delivery system for many viral vaccines. However, few studies have used this efficient antigen carrier for bacterial vaccine development. In this study, we eliminated the toxin activity domain of toxin B by constructing a recombinant protein rTcdB consists of residues 1852-2363 of TcdB receptor binding domain. The rTcdB was encapsulated in nanoparticles composed of γ-PGA and chitosan. Three rounds of intraperitoneal vaccination led to high anti-TcdB antibody responses and afforded mice full protection mice from lethal dose of C. difficile spore challenge. Protection was associated with high levels of toxin-neutralizing antibodies, and the rTcdB-encapsulated NPs elicited a longer-lasting antibody titers than antigen with the conventional adjuvant, aluminum hydroxide. Significant reductions in the level of proinflammatory cytokines and chemokines were observed in vaccinated mouse. These results suggested that polymeric nanocomplex-based vaccine design can be useful in developing vaccine against C. difficile infections.

Structural Insights into Substrate Recognition by Clostridium difficile Sortase

Sortases function as cysteine transpeptidases that catalyze the covalent attachment of virulence-associated surface proteins into the cell wall peptidoglycan in Gram-positive bacteria. The substrate proteins targeted by sortase enzymes have a cell wall sorting signal (CWSS) located at the C-terminus. Up to date, it is still not well understood how sortases with structural resemblance among different classes and diverse species of bacteria achieve substrate specificity. In this study, we focus on elucidating the molecular basis for specific recognition of peptide substrate PPKTG by Clostridium difficile sortase B (Cd-SrtB). Combining structural studies, biochemical assays and molecular dynamics simulations, we have constructed a computational model of Cd-SrtB_ΔN26-PPKTG complex and have validated the model by site-directed mutagensis studies and fluorescence resonance energy transfer (FRET)-based assay. Furthermore, we have revealed that the fourth amino acid in the N-terminal direction from cleavage site of PPKTG forms specific interaction with Cd-SrtB and plays an essential role in configuring the peptide to allow more efficient substrate-specific cleavage by Cd-SrtB.

Predominance of Clostridium difficile Ribotypes 017 and 078 among Toxigenic Clinical Isolates in Southern Taiwan

Ribotypes and toxin genotypes of clinical C. difficile isolates in Taiwan are rarely reported. A prospective surveillance study from January 2011 to January 2013 was conducted at the medical wards of a district hospital in southern Taiwan. Of the first toxigenic isolates from 120 patients, 68 (56.7%) of 120 isolates possessed both tcdA and tcdB. Of 52 (43.3%) with tcdB and truncated tcdA (tcdA-/tcdB+), all were ribotype 017 and none had binary toxin or tcdC deletion. Eighteen (15%) toxigenic isolates harbored binary toxins (cdtA and cdtB) and all had tcdC deletion, including Δ39 (C184T) deletion (14 isolates), Δ18 in-frame deletion (3 isolates), and Δ18 (Δ117A) deletion (1 isolate). Eleven of 14 isolates with Δ39 (C184T) deletion belonged to the ribotype 078 family, including ribotype 127 (6 isolates), ribotype 126 (4 isolates), and ribotype 078 (1 isolate). Among 8 patients with consecutive C. difficile isolates, these isolates from 6 (75%) patients were identical, irrespective of the presence or absence of diarrhea, suggestive of persistent fecal carriage or colonization. In conclusion in southern Taiwan, ribotype 017 isolates with a tcdA-/tcdB+ genotype were not uncommon and of C. difficile isolates with binary toxin, the ribotype 078 family was predominant.

Prevalence and characterization of enterotoxigenic Bacteroides fragilis and toxigenic Clostridium difficile in a Taipei emergency department

BACKGROUND/PURPOSE

Enterotoxigenic Bacteroides fragilis (ETBF) and toxin-encoding Clostridium difficile (TXCD) are associated with gastroenteritis. Routine anaerobic blood culture for recovery of these anaerobic pathogens is not used for the detection of their toxins, especially for toxin-variant TXCD. The aim of this study was to investigate the prevalence and risk factors of the genotypes of these anaerobes in patients with acute diarrheal illnesses.

METHODS

The data and samples of 513 patients with gastroenteritis were collected in a Taipei emergency department from March 1, 2006 to December 31, 2009. Nonenterotoxigenic B. fragilis (NTBF) and ETBF and the toxin genotypes of TXCD were detected by molecular methods.

RESULTS

The prevalence rates of NTBF, ETBF, and TXCD infections were 33.14%, 1.56%, and 2.34%, respectively. ETBF infections often occurred in the elderly (average age = 67.13 years) and during the cold, dry winters. TXCD infections were widely distributed in age and often occurred in the warm, wet springs and summers. The symptoms of ETBF-infected patients were significantly more severe than those of NTBF-infected patients.

CONCLUSION

This study identified and analyzed the prevalence, risk factors, and clinical presentations of these anaerobic infections. Future epidemiologic and clinical studies are needed to understand the role of ETBF and TXCD in human gastroenteritis.

Lethality of sortase depletion in Actinomyces oris caused by excessive membrane accumulation of a surface glycoprotein

Sortase, a cysteine-transpeptidase conserved in Gram-positive bacteria, anchors on the cell wall many surface proteins that facilitate bacterial pathogenesis and fitness. Genetic disruption of the housekeeping sortase in several Gram-positive pathogens reported thus far attenuates virulence, but not bacterial growth. Paradoxically, we discovered that depletion of the housekeeping sortase SrtA was lethal for Actinomyces oris; yet, all of its predicted cell wall-anchored protein substrates (AcaA-N) were individually dispensable for cell viability. Using Tn5-transposon mutagenesis to identify factors that upend lethality of srtA deletion, we uncovered a set of genetic suppressors harbouring transposon insertions within genes of a locus encoding AcaC and a LytR-CpsA-Psr (LCP)-like protein. AcaC was shown to be highly glycosylated and dependent on LCP for its glycosylation. Upon SrtA depletion, the glycosylated form of AcaC, hereby renamed GspA, was accumulated in the membrane. Overexpression of GspA in a mutant lacking gspA and srtA was lethal; conversely, cells overexpressing a GspA mutant missing a membrane-localization domain were viable. The results reveal a unique glycosylation pathway in A. oris that is coupled to cell wall anchoring catalysed by sortase SrtA. Significantly, this novel phenomenon of glyco-stress provides convenient cell-based assays for developing a new class of inhibitors against Gram-positive pathogens.

The crystal structure analysis of group B Streptococcus sortase C1: a model for the "lid" movement upon substrate binding

A unique feature of the class-C-type sortases, enzymes essential for Gram-positive pilus biogenesis, is the presence of a flexible "lid" anchored in the active site. However, the mechanistic details of the "lid" displacement, suggested to be a critical prelude for enzyme catalysis, are not yet known. This is partly due to the absence of enzyme-substrate and enzyme-inhibitor complex crystal structures. We have recently described the crystal structures of the Streptococcus agalactiae SAG2603 V/R sortase SrtC1 in two space groups (type II and type III) and that of its "lid" mutant and proposed a role of the "lid" as a protector of the active-site hydrophobic environment. Here, we report the crystal structures of SAG2603 V/R sortase C1 in a different space group (type I) and that of its complex with a small-molecule cysteine protease inhibitor. We observe that the catalytic Cys residue is covalently linked to the small-molecule inhibitor without lid displacement. However, the type I structure provides a view of the sortase SrtC1 lid displacement while having structural elements similar to a substrate sorting motif suitably positioned in the active site. We propose that these major conformational changes seen in the presence of a substrate mimic in the active site may represent universal features of class C sortase substrate recognition and enzyme activation.

Differential response of Streptococcus mutans towards friend and foe in mixed-species cultures

In the oral biofilm, the 'mitis' streptococci are among the first group of organisms to colonize the tooth surface. Their proliferation is thought to be an important factor required for antagonizing the growth of cariogenic species such as Streptococcus mutans. In this study, we used a three-species mixed culture to demonstrate that another ubiquitous early colonizing species, Veillonella parvula, can greatly affect the outcome of the competition between a pair of antagonists such as S. mutans and Streptococcus gordonii. Transcriptome analysis further revealed that S. mutans responds differentially to its friend (V. parvula) and foe (S. gordonii). In the mixed culture with S. gordonii, all but one of the S. mutans sugar uptake and metabolic genes were downregulated, while genes for alternative energy source utilization and H₂O₂ tolerance were upregulated, resulting in a slower but persistent growth. In contrast, when cultured with V. parvula, S. mutans grew equally well or better than in monoculture and exhibited relatively few changes within its transcriptome. When V. parvula was introduced into the mixed culture of S. mutans and S. gordonii, it rescued the growth inhibition of S. mutans. In this three-species environment, S. mutans increased the expression of genes required for the uptake and metabolism of minor sugars, while genes required for oxidative stress tolerance were downregulated. We conclude that the major factors that affect the competition between S. mutans and S. gordonii are carbohydrate utilization and H₂O₂ resistance. The presence of V. parvula in the tri-species culture mitigates these two major factors and allows S. mutans to proliferate, despite the presence of S. gordonii.

Genes involved in the repression of mutacin I production in Streptococcus mutans

Streptococcus mutans is considered a primary pathogen for human dental caries. Its ability to produce a variety of peptide antibiotics called mutacins may play an important role in its invasion and establishment in the dental biofilm. S. mutans strain UA140 produces two types of mutacins, the lantibiotic mutacin I and the non-lantibiotic mutacin IV. In a previous study, we constructed a random insertional-mutation library to screen for genes involved in regulating mutacin I production, and found 25 genes/operons that have a positive effect on mutacin I production. In this study, we continued our previous work to identify genes that are negatively involved in mutacin I production. By using a high-phosphate brain heart infusion agar medium that inhibited mutacin I production of the wild-type, we isolated 77 clones that consistently produced mutacin I under repressive conditions. From the 34 clones for which we were able to obtain a sequence, 17 unique genes were identified. These genes encompass a variety of functional groups, including central metabolism, surface binding and sugar transport, and unknown functions. Some of the 17 mutations were further characterized and shown to increase mutacin gene expression during growth when the gene is usually not expressed in the wild-type. These results further demonstrate an intimate and intricate connection between mutacin production and the overall cellular homeostasis.

Complementation of a Clostridium perfringens spo0A mutant with wild-type spo0A from other Clostridium species

To evaluate whether C. perfringens can be used as a model organism for studying the sporulation process in other clostridia, C. perfringens spo0A mutant IH101 was complemented with wild-type spo0A from four different Clostridium species. Wild-type spo0A from C. acetobutylicum or C. tetani, but not from C. botulinum or C. difficile, restored sporulation and enterotoxin production in IH101. The ability of spo0A from C. botulinum or C. difficile to complement the lack of spore formation in IH101 might be due, at least in part, to the low levels of spo0A transcription and Spo0A production.

Inorganic phosphate induces spore morphogenesis and enterotoxin production in the intestinal pathogen Clostridium perfringens

Clostridium perfringens enterotoxin (CPE) is an important virulence factor for food poisoning and non-food borne gastrointestinal (GI) diseases. Although CPE production is strongly regulated by sporulation, the nature of the signal(s) triggering sporulation remains unknown. Here, we demonstrated that inorganic phosphate (Pi), and not pH, constitutes an environmental signal inducing sporulation and CPE synthesis. In the absence of Pi-supplementation, C. perfringens displayed a spo0A phenotype, i.e., absence of polar septation and DNA partitioning in cells that reached the stationary phase of growth. These results received support from our Northern blot analyses which demonstrated that Pi was able to counteract the inhibitory effect of glucose at the onset of sporulation and induced spo0A expression, indicating that Pi acts as a key signal triggering spore morphogenesis. In addition to being the first study reporting the nature of a physiological signal triggering sporulation in clostridia, these findings have relevance for the development of antisporulation drugs to prevent or treat CPE-mediated GI diseases in humans.

Disruption of the gene (spo0A) encoding sporulation transcription factor blocks endospore formation and enterotoxin production in enterotoxigenic Clostridium perfringens type A

This study identified a functional spo0A ORF in enterotoxigenic Clostridium perfringens type A. To evaluate the function of spo0A, an isogenic spo0A knock-out mutant was constructed. The spo0A mutant was unable to form endospores and produce enterotoxin, however, these defects could be restored by complementing the mutant with a recombinant plasmid carrying the wild-type spo0A gene. These results provide evidence that spo0A expression is essential for sporulation and enterotoxin production in C. perfringens.

A simple chemiluminescence assay for detecting oxidative stress in ischemic limb injury

This study was designed to evaluate a simple, sensitive, nonstimulated chemiluminescence assay to measure the oxidative stress production in the whole blood of rabbits after an ischemic insult. By using an ultra-sensitive chemiluminescence (CL) analyzer and lucigenin amplification, the assay system can be performed without leukocyte isolation and stimulant administration. The blood CL levels of healthy rabbits were 122 +/- 18 counts/10 s. After 8 h of ischemia, the CL levels of whole blood immediately after reperfusion, 1 h, 2 h, 24 h, 48 h, 7 days, and 14 days of reperfusion were 409 +/- 78 counts/10 s, 283 +/- 55 counts/10 s, 256 +/- 43 counts/10 s, 228 +/- 33 counts/10 s, 185 +/- 32 counts/10 s, 160 +/- 16 counts/10 s, and 119 +/- 15 counts/10 s. The differences were statistically significant between the control and samples obtained up to 24 h after reperfusion. The corresponding creatine phosphate kinase (CPK) levels of the rabbits in this study were 938 +/- 43 U/l for the control blood sample and 5921 +/- 498 U/l, 6948 +/- 427 U/l, 6860 +/- 1115 U/l, 5763 +/- 516 U/l, 1545 +/- 291 U/l, 478 +/- 60 U/l, and 458 +/- 48 U/l for the experimental blood samples. The CPK levels of the blood samples before 24 h and after 7 days of reperfusion were significantly different to that of the control blood sample. The changes in the CL and CPK levels were quite similar before 48 h reperfusion. This assay has proved to be valuable in the quantitative measurement of ischemic insults of skeletal muscles.

Mutagenicity of dipyridyls and their methylated derivatives in Salmonella typhimurium/rat liver microsome system

The Salmonella/microsome assay with strains TA97, TA98, TA100, TA1535, TA1537 and TA1538 was used to examine the potential mutagenicity of 5 dipyridyls, 1 tripyridyl, 3 dipyridinium diiodides and 2 pyridinium monoiodides. The widely used herbicide paraquat (1,1-dimethyl-4,4'-dipyridinium diiodide) and its precursor 4,4'-dipyridyl gave weak and marginal mutagenic activity to Salmonella typhimurium TA1535 and TA1538 in the presence of S9-mix. Significantly high mutagenicity was obtained with 2,2'-, 3,3'-, 2,3'-, and 2,4'-dipyridyls, 2,2',2"-tripyridyl, and 5 pyridinium salts under the same conditions. The positive mutagenic response of 2,2',2"-tripyridyl suggests that higher polymers of pyridine contaminating paraquat preparations might be mutagenic. The dose-response curves of 1,1-dimethyl-3,3'-dipyridinium diiodide and 1,1'-dimethyl-2,2'-dipyridinium diiodide revealed an exponential relationship between the number of induced revertants and the compound concentrations. The results suggested that the mechanism of mutation induced by these two compounds might be attributed to the chain reactions of their free-radicals with molecular oxygen.

Clostridium perfringens: Sporulation, Spore Resistance and Germination

Clostridium perfringens are Gram-positive, endospore-forming, anaerobic bacteria with the ability to cause enteric diseases both in human and domesticated animals. As one of the leading cause of food-borne illness in the United States, certain C. perfringens type A isolates exert their action through the production of C. perfringens enterotoxin (CPE), which is expressed only during spore formation. In addition, C. perfringens spores are highly resistant to heat and other environmental factors. Since genome sequences of three C. perfringens strains have been annotated and made public, efforts have been made towards understanding the initiation of sporulation and identifying the key differences between Clostridium and Bacillus sporulation phosphorelay. Small, acid soluble spore proteins (SASPs) have been shown to be required for resistance of C. perfringens spores to heat. Work is also underway to identify nutrient signals required for C. perfringens spore germination. Keywords: Clostridium perfringens, Endospore, Small, acid soluble spore protein (SASP), Heat resistance, GerminationDOI: http://dx.doi.org/10.3329/bjm.v24i1.1229 Bangladesh J Microbiol, Volume 24, Number 1, June 2007, pp 1-8