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Clostridium septicum is a Gram-positive anaerobic bacillus that causes serious, life-threatening infections, including aggressive septicemia and myonecrosis. Clostridial myonecrosis can be broadly classified into two defined clinical presentations: traumatic and spontaneous. Clostridium perfringens is the most common cause of traumatic myonecrosis, while C. septicum is the most common etiological agent of spontaneous myonecrosis. Although rarely clinically encountered, C. septicum infections are often fatal. Disease is thought to be initiated by the transfer of C. septicum from the gut to the bloodstream through gastric epithelial lesions. C. septicum infections are strongly associated with colonic and hematological malignancy, which can cause or facilitate the formation of lesions. Subsequent bacteremia allows the establishment of C. septicum at distal anatomical sites, which can manifest as spontaneous myonecrosis, or necrotizing enterocolitis in neutropenic patients. Here, we present a summary of the current knowledge related to the pathogen, highlighting clinical manifestations, molecular pathogenesis, and the diagnostic significance of C. septicum in the clinical setting.

Morbidity and mortality attributed to Clostridium difficile infection (CDI) have increased over the past 20 years. Currently, antibiotics are the only US FDA-approved treatment for primary C. difficile infection, and these are, ironically, associated with disease relapse and the threat of burgeoning drug resistance. We previously showed that non-toxin virulence factors play key roles in CDI, and that colonization factors are critical for disease. Specifically, a C. difficile adhesin, Surface Layer Protein A (SlpA) is a major contributor to host cell attachment. In this work, we engineered Syn-LAB 2.0 and Syn-LAB 2.1, two synthetic biologic agents derived from lactic acid bacteria, to stably and constitutively express a host-cell binding fragment of the C. difficile adhesin SlpA on their cell-surface. Both agents harbor conditional suicide plasmids expressing a codon-optimized chimera of the lactic acid bacterium's cell-wall anchoring surface-protein domain, fused to the conserved, highly-adherent, host-cell-binding domain of C. difficile SlpA. Both agents also incorporate engineered biocontrol, obviating the need for any antibiotic selection. Syn-LAB 2.0 and Syn-LAB 2.1 possess positive biophysical and in vivo properties compared with their parental antecedents in that they robustly and constitutively display the SlpA chimera on their cell surface, potentiate human intestinal epithelial barrier function in vitro, are safe, tolerable and palatable to Golden Syrian hamsters and neonatal piglets at high daily doses, and are detectable in animal feces within 24 hours of dosing, confirming robust colonization. In combination, the engineered strains also delay (in fixed doses) or prevent (when continuously administered) death of infected hamsters upon challenge with high doses of virulent C. difficile. Finally, fixed-dose Syn-LAB ameliorates diarrhea in a non-lethal model of neonatal piglet enteritis. Taken together, our findings suggest that the two synthetic biologics may be effectively employed as non-antibiotic interventions for CDI.

Clostridium difficile is responsible for severe diarrhea in humans that may cause death. Spores are the infectious form of C. difficile, which germinate into toxin-producing vegetative cells in response to bile acids. Recently, we discovered that C. difficile cells possess three complex polysaccharides (PSs), named PSI, PSII, and PSIII, in which PSI was only associated with a hypervirulent ribotype 027 strain, PSII was hypothesized to be a common antigen, and PSIII was a water-insoluble polymer. Here, we show that (i) C. difficile spores contain, at least in part, a d -glucan, (ii) PSI is not a ribotype 027-unique antigen, (iii) common antigen PSII may in part be present as a low molecular weight lipoteichoic acid, (iv) selective hydrolysis of PSII yields single PSII repeat units, (v) the glycosyl diester–phosphate linkage affords high flexibility to PSII, and (vi) that PSII is immunogenic in sows. Also, with the intent of creating a dual anti-diarrheal vaccine against C. difficile and enterotoxin Escherichia coli (ETEC) infections in humans, we describe the conjugation of PSII to the ETEC-associated LTB enterotoxin.

Toxigenic Clostridium difficile strains produce two toxins (TcdA and TcdB) during the stationary phase of growth and are the leading cause of antibiotic-associated diarrhea. C. difficile isolates of the molecular type NAP1/027/BI have been associated with severe disease and hospital outbreaks worldwide. It has been suggested that these “hypervirulent” strains produce larger amounts of toxin and that a mutation in a putative negative regulator (TcdC) allows toxin production at all growth phases. To rigorously explore this possibility, we conducted a quantitative examination of the toxin production of multiple hypervirulent and nonhypervirulent C. difficile strains. Toxin gene ( tcdA and tcdB ) and toxin gene regulator ( tcdR and tcdC ) expression was also monitored. To obtain additional correlates for the hypervirulence phenotype, sporulation kinetics and efficiency were measured. In the exponential phase, low basal levels of tcdA , tcdB , and tcdR expression were evident in both hypervirulent and nonhypervirulent strains, but contrary to previous assumptions, toxin levels were below the detectable thresholds. While hypervirulent strains displayed robust toxin production during the stationary phase of growth, the amounts were not significantly different from those of the nonhypervirulent strains tested; further, total toxin amounts were directly proportional to tcdA , tcdB , and tcdR gene expression. Interestingly, tcdC expression did not diminish in stationary phase, suggesting that TcdC may have a modulatory rather than a strictly repressive role. Comparative genomic analyses of the closely related nonhypervirulent strains VPI 10463 (the highest toxin producer) and 630 (the lowest toxin producer) revealed polymorphisms in the tcdR ribosome binding site and the tcdR-tcdB intergenic region, suggesting that a mechanistic basis for increased toxin production in VPI 10463 could be increased TcdR translation and read-through transcription of the tcdA and tcdB genes. Hypervirulent isolates produced significantly more spores, and did so earlier, than all other isolates. Increased sporulation, potentially in synergy with robust toxin production, may therefore contribute to the widespread disease now associated with hypervirulent C. difficile strains.

Intestinal bacteria drive the formation of lymphoid tissues, and in rabbit, bacteria also promote development of the preimmune Ab repertoire and positive selection of B cells in GALT. Previous studies indicated that Bacillus subtilis promotes B cell follicle formation in GALT, and we investigated the mechanism by which B. subtilis stimulates B cells. We found that spores of B. subtilis and other Bacillus species, including Bacillus anthracis, bound rabbit IgM through an unconventional, superantigen-like binding site, and in vivo, surface molecules of B. anthracis spores promoted GALT development. Our study provides direct evidence that B cell development in GALT may be driven by superantigen-like molecules, and furthermore, that bacterial spores modulate host immunity.

Clostridium difficile is a leading cause of antibiotic-associated diarrhea, and a significant etiologic agent of healthcare-associated infections. The mechanisms of attachment and host colonization of C. difficile are not well defined. We hypothesize that non-toxin bacterial factors, especially those facilitating the interaction of C. difficile with the host gut, contribute to the initiation of C. difficile infection. In this work, we optimized a completely anaerobic, quantitative, epithelial-cell adherence assay for vegetative C. difficile cells, determined adherence proficiency under multiple conditions, and investigated C. difficile surface protein variation via immunological and DNA sequencing approaches focused on Surface-Layer Protein A (SlpA). In total, thirty-six epidemic-associated and non-epidemic associated C. difficile clinical isolates were tested in this study, and displayed intra- and inter-clade differences in attachment that were unrelated to toxin production. SlpA was a major contributor to bacterial adherence, and individual subunits of the protein (varying in sequence between strains) mediated host-cell attachment to different extents. Pre-treatment of host cells with crude or purified SlpA subunits, or incubation of vegetative bacteria with anti-SlpA antisera significantly reduced C. difficile attachment. SlpA-mediated adherence-interference correlated with the attachment efficiency of the strain from which the protein was derived, with maximal blockage observed when SlpA was derived from highly adherent strains. In addition, SlpA-containing preparations from a non-toxigenic strain effectively blocked adherence of a phylogenetically distant, epidemic-associated strain, and vice-versa. Taken together, these results suggest that SlpA plays a major role in C. difficile infection, and that it may represent an attractive target for interventions aimed at abrogating gut colonization by this pathogen.

Clostridium difficile infection is the leading cause of antibiotic- and healthcare-associated diarrhea, and its containment and treatment imposes a significant financial burden, estimated to be over $3 billion in the USA alone. Since the year 2000, CDI epidemics/outbreaks have occurred in North America, Europe and Asia. These outbreaks have been variously associated with, or attributed to, the emergence of Clostridium difficile strains with increased virulence, an increase in resistance to commonly used antimicrobials such as the fluoroquinolones, or host susceptibilities, including the use of gastric acid suppressants, to name a few. Efforts to elucidate C. difficile pathogenic mechanisms have been hampered by a lack of molecular tools, manipulatable animal models, and genetic intractability of clinical C. difficile isolates. However, in the past 5 y, painstaking efforts have resulted in the unraveling of multiple C. difficile virulence-associated pathways and mechanisms. We have recently reviewed the disease, its associated risk factors, transmission and interventions (Viswanathan, Gut Microbes 2010). This article summarizes genetics, non-toxin virulence factors, and host-cell biology associated with C. difficile pathogenesis as of 2011, and highlights those findings/factors that may be of interest as future intervention targets.

Poultry necrotic enteritis (NE) is caused by specific strains of Clostridium perfringens, most of which are type A. The role of alpha toxin (CPA) in NE has been called into question by the finding that an engineered cpa mutant retains full virulence in vivo[9]. This is in contrast to the finding that immunization with CPA toxoids protects against NE. We confirmed the earlier findings, in that 14-day-old Cornish × Rock broiler chicks challenged with a cpa mutant developed lesions compatible with NE in >90% of birds inoculated with the mutant. However, CPA was detected in amounts ranging from 10 to >100 ng per g of gut contents and mucosa in birds inoculated with the cpa mutant, the wildtype strain from which the mutant was constructed, and our positive control strain. There was a direct relationship between lesion severity and amount of CPA detected (R = 0.89-0.99). These findings suggest that the role of CPA in pathogenesis of NE requires further investigation.