Necrotic enteritis-producing strains of Clostridium perfringens displace non-necrotic enteritis strains from the gut of chicks

Genetic diversity and prevalence of netB in Clostridium perfringens isolated from a broiler flock affected by mild necrotic enteritis

This study was undertaken to examine the genetic diversity of Clostridium perfringens isolated from a single broiler flock reared without in-feed antimicrobials (antibacterial growth promoters and anticoccidials) and affected by mild necrotic enteritis (NE). We used pulsed-field gel electrophoresis (PFGE) to investigate the genetic diversity of C. perfringens isolates from broilers of varying disease status, and from litter. The prevalence of the toxin gene netB was also investigated. Altogether 32 PFGE genotypes were found among 88 isolates. Several genotypes were detected in C. perfringens-associated organ lesions from chickens that were sampled at random and alive without clinical symptoms, suggesting that these genotypes proliferated concurrently in such lesions. More than 90% of all isolates from NE-specific organ lesions carried netB which codes for a recently described pore-forming toxin. NetB positive isolates were less predominant in non-lesion samples from broilers affected by NE, and found infrequently or not at all in healthy birds and isolates from litter. These findings show that the presence of netB in C. perfringens strains is associated with NE and suggest that mild NE differs from severe NE with regard to C. perfringens genotype diversity.

Sequence variation in the alpha-toxin encoding plc gene of Clostridium perfringens strains isolated from diseased and healthy chickens

The aim of the present study was to analyse the genetic diversity of the alpha-toxin encoding plc gene and the variation in alpha-toxin production of Clostridium perfringens type A strains isolated from presumably healthy chickens and chickens suffering from either necrotic enteritis (NE) or cholangio-hepatitis. The alpha-toxin encoding plc genes from 60 different pulsed-field gel electrophoresis (PFGE) types (strains) of C. perfringens were sequenced and translated in silico to amino acid sequences and the alpha-toxin production was investigated in batch cultures of 45 of the strains using an enzyme-linked immunosorbent assay (ELISA) approach. Overall, the truncated amino acid sequences showed close similarity (>98% at the amino acid level) to previously reported sequences from chicken-derived C. perfringens isolates. Variations were however observed in 23 out of 379 aa positions leading to the definition of 26 different alpha-toxin sequence types among the 60 strains. Moreover, a type II intron of 834 non-coding nucleotides was identified in the plc gene of three of the investigated strains. The in vitro alpha-toxin production investigated in 45 of the strains, including the three harbouring the intron, revealed no correlation between PFGE type, alpha-toxin sequence type, health status of the host chickens and level of alpha-toxin production. It is therefore concluded that neither plc gene type nor alpha-toxin production level seems to correlate to origin (healthy or diseased chicken) of the C. perfringens strains.

Recombinant attenuated Salmonella enterica serovar typhimurium expressing the carboxy-terminal domain of alpha toxin from Clostridium perfringens induces protective responses against necrotic enteritis in chickens

Clostridium perfringens-induced necrotic enteritis (NE) is a widespread disease in chickens that causes high mortality and reduced growth performance. Traditionally, NE was controlled by the routine application of antimicrobials in the feed, a practice that currently is unpopular. Consequently, there has been an increase in the occurrence of NE, and it has become a threat to the current objective of antimicrobial-free farming. The pathogenesis of NE is associated with the proliferation of C. perfringens in the small intestine and the secretion of large amounts of alpha toxin, the major virulence factor. Since there is no vaccine for NE, we have developed a candidate live oral recombinant attenuated Salmonella enterica serovar Typhimurium vaccine (RASV) that delivers a nontoxic fragment of alpha toxin. The 3' end of the plc gene, encoding the C-terminal domain of alpha toxin (PlcC), was cloned into plasmids that enable the expression and secretion of PlcC fused to a signal peptide. Plasmids were inserted into Salmonella enterica serovar Typhimurium host strain chi8914, which has attenuating pabA and pabB deletion mutations. Three-day-old broiler chicks were orally immunized with 10(9) CFU of the vaccine strain and developed alpha toxin-neutralizing serum antibodies. When serum from these chickens was added into C. perfringens broth cultures, bacterial growth was suppressed. In addition, immunofluorescent microscopy showed that serum antibodies bind to the bacterial surface. The immunoglobulin G (IgG) and IgA titers in RASV-immunized chickens were low; however, when the chickens were given a parenteral boost injection with a purified recombinant PlcC protein (rPlcC), the RASV-immunized chickens mounted rapid high serum IgG and bile IgA titers exceeding those primed by rPlcC injection. RASV-immunized chickens had reduced intestinal mucosal pathology after challenge with virulent C. perfringens. These results indicate that oral RASV expressing an alpha toxin C-terminal peptide induces protective immunity against NE.