Clostridium perfringens type A causes poultry necrotic enteritis (NE), an enteric disease of considerable economic importance. A novel toxin, NetB, is critical to NE pathogenesis and closely associated with virulent strains. We recently demonstrated that netB resides on a large, conjugative plasmid within a 42 kb pathogenicity locus (NELoc-1) that, in conjunction with two other loci (NELoc-2 and 3), is highly conserved in virulent strains. Though plasmid-encoded genes are clearly important to NE pathogenesis, it is not known whether a specific chromosomal background is associated with virulent strains.
To study further the genomic signature of NE-associated strains, we used a C. perfringens microarray based on two NE-producing strains to analyse the gene content of a set of 54 C. perfringens isolates, 25 from birds with NE and 29 from asymptomatic birds. Pulsed field gel electrophoresis (PFGE) demonstrated that the isolates are genetically distinct. A total of 128 genes significantly associated with netB were identified, including genes related to iron-acquisition and carbohydrate utilization.
Phylogenetic analysis of CGH data placed 90% of the poultry isolates into three major clusters (I-III). Group I (n=17) consisted entirely of netB-negative isolates while Groups II (n=18) and III (n=15) were comprised of 61% and 67% netB-positive isolates, respectively. Several chromosomal loci were identified that differentiate Groups II and III, including genes for dTDP-L-rhamnose biosynthesis, D-glucuronate catabolism and capsular polysaccharide.
These findings suggest that a specific chromosomal background is predominantly associated with netB-positive strains, consisting of supplementary fitness-related genes that likely enhance virulence. Furthermore, this chromosomal background can be further divided into two main lineages that are predicted to differ in terms of carbon utilization and serotype.