Necrotic enteritis (NE) is an important enteric disease in poultry, and Clostridium perfringens (CP) type A strains are the primary etiology. NE is responsible for annual losses of US $6 billion to the poultry industry in the United States. An increase in the incidence of NE has been also associated with withdrawal of antibiotic growth promoters from poultry feed. In this study, CP strains isolated from healthy and NE-afflicted birds were characterized microbiologically and molecularly, and their virulence was experimentally tested in chickens. All strains were hemolytic, lecithinase positive, and identified as CP by biochemical tests. Three distinct colony morphologies were seen in brain-heart infusion media with 0.3% agarose, FeSO4, and ZnCl2. The CP strains responded differently to iron chelation with 2,2'-bidypinol. PCR toxinotyping showed that all tested strains were alpha toxin-positive, seven (N11, N10, CP1, CP5, CP13, JGS, and Del1) were beta2-toxin-positive, and only one (Del1) was necrotic enteritis toxin B-like-positive. In vivo studies indicated that most isolates, including strain N11 isolated from the normal chicken gut, were sufficiently virulent to produce NE disease in the Eimeria/CP dual infection model. The Del1 and N11 strains merit further investigation to identify their virulence factors and immune-protective antigens.
Keywords: Clostridium perfringens; Eimeria; cpa; cpb2; iron; necrotic enteritis; netB; virulence.