A previously unknown pore forming toxin, called NetB toxin, which is produced by some Australian strains of Clostridium perfringens has recently been reported. This toxin was reported to be critical to the development of the disease necrotic enteritis, in chickens. To investigate the occurrence of the toxin gene (netB) in non-Australian C. perfringens strains, one hundred and six American isolates of C. perfringens were examined. Ninety-two isolates were from chickens, and 14 were from cattle. The netB gene was found in 14 isolates from chickens (7 from chickens with necrotic enteritis, and 7 from unrelated chickens with no evidence of necrotic enteritis). The netB gene was also detected in an isolate recovered from a 3-year-old cow with liver abscesses. The products of all positive netB PCR reactions were sequenced, and these showed 100% nucleotide identity to the netB sequence published in GenBank. Five isolates which had been recovered from five chickens with necrotic enteritis (from four flocks) were netB negative. An additional 24 isolates recovered from one of these lesioned chickens were also netB negative. The present study represents the first study of C. perfringens isolates outside Australia for netB, and the first identification of netB in an isolate from a species other than chickens. The results indicate that the role of NetB in the induction of necrotic enteritis needs to be further investigated, by determining the disease producing capability of both netB positive strains recovered from normal chickens, and netB negative strains recovered from chickens with necrotic enteritis.
"ositive strains isolated from animals affected by NE and healthy chickens has been found . However , the per - centage of positive strains in NE isolates was only 53 . 3% and , in addition , even if in low percentage ( 17 . 4% ) , CP that carry NetB gene were isolated also in healthy animals . Our results are in agreement with the data obtained by Martin et al . ( 2009 ) and , though they confirm the involvement of NetB toxin in the pathogenesis of NE , prompt to consid - er that also other pathogenic mechanisms could play an important role on NE appear - ance ."
"Existing studies ascertaining the prevalence of netB and tpeL have been limited to certain geographic populations of CP, mainly in Australia, Belgium, Denmark, Sweden, and Canada  . In the United States, studies on the prevalence of these genes have analyzed CP populations from New England, New York, and Pennsylvania . The relatively small number of sampled CP populations underlines a need for more analysis to determine the importance of these genes on a worldwide scale. "
[Show abstract][Hide abstract] ABSTRACT: Some studies have shown that the NetB toxin may be an important virulence factor of Clostridium perfringens associated necrotic enteritis in poultry. Additionally, research has shown that strains of C. perfringens positive for both the netB gene and a second toxin-encoding gene, tpeL, appear to be more virulent than strains with only netB. In the past, detection of these genes has been performed relatively inefficiently using two single locus PCRs. This report describes a novel multiplex PCR developed to detect netB and tpeL simultaneously in C. perfringens strains isolated from cases of necrotic enteritis in broilers, providing a more efficient diagnostic tool in the screening of strains for these genes.
"Recently, a secreted β-pore forming toxin, NetB, has been isolated from a virulent chicken isolate of C. perfringens and shown to be essential for disease induction . NetB toxin has been found in most C. perfringens isolates from necrotic enteritis-diseased birds, but is uncommon in isolates recovered from healthy birds [15-17]. As an important virulence factor, NetB represents an attractive vaccine candidate, as shown in a recent study where vaccination with NetB induced some protection of broiler birds against experimental necrotic enteritis . "
[Show abstract][Hide abstract] ABSTRACT: NetB toxin from Clostridium perfringens is a major virulence factor in necrotic enteritis in poultry. In this study the efficacy of NetB as a vaccine antigen to protect chickens from necrotic enteritis was examined. Broiler chickens were immunized subcutaneously with purified recombinant NetB (rNetB), formalin treated bacterin and cell free toxoid with or without rNetB supplementation. Intestinal lesion scores and NetB antibody levels were measured to determine protection after mild oral gavage, moderate in-feed and heavy in-feed challenges with virulent C. perfringens isolates. Birds immunized with rNetB were significantly protected against necrotic enteritis when challenged with a mild oral dose of virulent bacteria, but were not protected when a more robust challenge was used. Bacterin and cell free toxoid without rNetB supplementation did not protect birds from moderate and severe in-feed challenge. Only birds immunized with bacterin and cell free toxoid supplemented with rNetB showed significant protection against moderate and severe in-feed challenge, with the later giving the greatest protection. Higher NetB antibody titres were observed in birds immunized with rNetB compared to those vaccinated with bacterin or toxoid, suggesting that the in vitro levels of NetB produced by virulent C. perfringens isolates are too low to induce the development of a strong immune response. These results suggest that vaccination with NetB alone may not be sufficient to protect birds from necrotic enteritis in the field, but that in combination with other cellular or cell-free antigens it can significantly protect chickens from disease.
Veterinary Research 07/2013; 44(1):54. DOI:10.1186/1297-9716-44-54 · 2.82 Impact Factor
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