Intra-species growth-inhibition by Clostridium perfringens is a possible virulence trait in necrotic enteritis in broilers

Abstract

Necrotic enteritis in broiler chickens is associated with Clostridium perfringens type A, carrying the NetB toxin. C. perfringens type A is also a member of the normal intestinal microbiota of broilers. Clinically healthy chickens carry several different C. perfringens clones in their intestine. In flocks suffering from necrotic enteritis, however, mostly only one single clone is isolated from the gut of all the diseased animals. Selective proliferation of these clinical outbreak strains in the gut and spread within the flock seems likely, but an explanation has not yet been given. The hypothesis that necrotic enteritis associated C. perfringens strains might suppress the growth of normal microbiota C. perfringens strains, was therefore tested. Twenty-six C. perfringens strains isolated from healthy broilers and 24 clinical outbreak isolates were evaluated for their ability to induce intra-species growth-inhibition in an in vitro setup. A significantly higher proportion of the C. perfringens clinical outbreak strains inhibited the growth of other C. perfringens strains compared to C. perfringens strains isolated from the gut of healthy chickens. It is proposed that, in addition to toxin production, intra-species growth-inhibition may be a virulence trait that contributes to the ability of certain C. perfringens strains to cause necrotic enteritis in broilers.

Introduction

Since the ban on growth-promoting antibiotics in animal feed in the European Union, Clostridium (C.) perfringens associated necrotic enteritis is re-emerging in broilers (Grave et al., 2004, Van Immerseel et al., 2004, Williams, 2005). Necrotic enteritis in poultry is associated with C. perfringens type A, carrying the NetB toxin (Keyburn et al., 2008, Van Immerseel et al., 2008). C. perfringens type A is also a member of the normal intestinal microbiota of broilers. Strains isolated from healthy broilers, however, do not induce necrotic enteritis in an experimental model using predisposing factors, in contrast to strains isolated from outbreaks of necrotic enteritis (Timbermont et al., 2008).

In C. perfringens isolates from healthy birds, a high degree of genetic diversity is found, even between isolates from the same animal. In contrast, different isolates from a flock suffering from a clinical outbreak are generally of the same Pulsed Field Gel Electrophoresis (PFGE) type, regardless of the animal or the part of the intestine from which the strain was isolated (Nauerby et al., 2003, Gholamiandehkordi et al., 2006). The reason for the presence of a single clone in necrotic enteritis outbreaks is not known. It is speculated that during an outbreak, certain C. perfringens strains have a competitive advantage over other C. perfringens strains in the broiler gut.

In the present study, strains isolated from healthy broilers and strains isolated from broilers suffering from necrotic enteritis were compared with respect to their capacity of intra-species growth-inhibition in an in vitro inhibition assay.