Characterization of quorum sensing system in Clostridium chauvoei.

Clostridium chauvoei causes fatal black quarter infection in cattle and buffaloes. The quorum sensing (QS) system, a bacterial cell to cell communication process, of the pathogen was characterized in the current study. The results indicated that C. chauvoei lacked luxS (autoinducer-2) based quorum sensing as detected by the sensor strain Vibrio harveyi BB170. This was supported by absence of luxS gene in C. chauvoei genome. However, the genomic analysis indicated the presence of agrBD system in all three genomes of C. chauvoei available at the NCBI database. The AgrD, which synthesizes QS messenger auto-inducing peptide, was a 44 amino acid protein which shared 59% identity and 75% similarity with AgrD of C. perfringens strain 13 and 56% identity (20% coverage) with Staphylococcus aureus N315. The functional cysteine amino acid was conserved in all the strains. The genomic organisation further suggests the presence of diguanylate cyclase, a gene responsible for synthesis of secondary messenger cyclic di-GMP, at 3' immediate downstream of agrD gene. The real time expression analysis for agrD gene indicated that expression was better at 37 °C (1.9-3.7 fold increase) compared to a higher temperature of 40 °C. However, stable expression was observed at different growth stages (log and early stationary phase) with 0.8-1.4 fold changes in expression pattern. The results indicate the presence of a constitutively expressed agrBD quorum sensing system in C. chauvoei.

Extracellular proteins of Clostridium chauvoei are protective in a mouse model.

The anaerobic bacillus Clostridium chauvoei is the causative agent of blackleg, a lethal disease that has an important impact on the sheep and cattle industry worldwide. Immunity to C. chauvoei is considered to be mainly anticellular, and for this reason there is scarce information about the immunogenicity of extracellular proteins. In this work variations in protein profiles, immune response by ELISA and protective capacity of culture supernatants of three C. chauvoei strains, collected at different growth phases, are reported. Sera raised against extracellular antigens also recognised cellular antigens of the same molecular masses. Partially purified cell-free supernatants and those concentrated 10 times by ultrafiltration (C-CFS), obtained at the early stationary phase of growth, induced a strong immunoprotective response, even at low doses, that was more marked for C. chauvoei strain ATCC 10092 (p < or = 0.05). With C-CFS formulations, a clear relationship was observed between IgG titres, protective capacity and concentration of the antigen doses, indicating a specific immune response.