Z-012. Highly Clonal Relationships among Isolates of Clostridium septicum Associated with Gangrenous Infections of Poultry
Clostridium septicum is a highly virulent but poorly understood anaerobic bacterium capable of establishing necrotizing tissue infections and forming heat resistant endospores. Disease is primarily facilitated by the organism’s ability to secrete numerous toxic products including a lethal pore-forming cytolysin. Spontaneously occurring clostridial myonecrosis involving C. septicum has recently reemerged as a concern for many poultry producers. However, despite its increasing prevalence, the epidemiology of infection and population structure of C. septicum remains largely unknown. In this study a multilocus sequence typing (MLST) scheme was developed and utilized to examine evolutionary relationships among a diverse collection of C. septicum isolates recovered from poultry flocks experiencing gangrenous C. septicum infections. The 108 isolates examined represented 42 turkey flocks and 24 different flocks of broiler chickens. Isolates were recovered predominantly from gangrenous lesions although isolates from livers, gastrointestinal tracts, spleens and blood were also tested. The loci chosen for the analysis were gyrA, groEL, dnaK, recA, tpi, ddl and glpK. Most of these loci were included because of their involvement in similar typing schemes published for C. perfringens and C. difficile. Results indicated a high level of conservation present within housekeeping genes of C. septicum when compared to that previously reported for the aforementioned species. Of the 4224bp of sequence data examined for each isolate, 99.7% (4212/4224) was absolutely conserved among the 108 isolates. Only one of the eight unique sequence types, or allelic profiles, identified among the isolates was recovered from both turkeys and broiler chickens indicating some host preference. Significant linkage disequilibrium was detected among the 108 avian isolates by calculating the index of association (Ia = 3.0662). This work suggests a predominantly clonal population structure for C. septicum, and a lack of genetic diversity that may be a reflection of a highly specialized pathogenic lifestyle.