Background Clostridium perfringens (C. perfringens), a major enteric pathogen, can lead to both clinical and subclinical disease in broiler chickens. 1 This bacterium was divided to five types (A, B, C, D and E) based on the presence of major toxins (α, β, ε and ι). It produced some important minor toxins such as enterotoxin, beta 2 , necrotic enteritis toxin B (NetB), TpeL and perfringolysin O (PFO). 2 C. perfringens is responsible for causing necrotic enteritis (NE) of poultry, especially by type A and rarely type C. 3 C. perfringens type A is the most frequently isolated clostridial type from NE cases. 4,5 NE is an economically important disease with severe gastro-intestinal signs in commercial broiler farms and was reported for the first time by Parish. 6 Two forms of NE were described: clinical and subclinical. 7 Clinical NE, primarily in young chickens (between two to six weeks), is characterized by severe necrosis in the mucosa of proximal jejunum and associated with high mortality rates. 8 Subclinical NE is led to a decreased performance (reduced growth, reduced feed efficiency) without mortality, due to the extensive mucosal damage. 9 Keyburn et al discovered a pore forming toxin of C. per-fringens which they named NetB and the encoding gene, netB and recognized this gene in C. perfringens isolates recovered from chickens. They showed the relationship between presence of netB gene and NE outbreaks and reported that NetB is critical to the development of NE, in chickens. 10 To our knowledge, there were not published data about NE outbreaks and responsible toxins for causing this disease in organic broiler farms. Objectives This study was firstly aimed to genotype the pathogenic C. perfringens isolates in organic broiler farms and secondly to assess the presence of netB gene among them and its occurrence with respect to the disease NE. Materials and Methods Sampling A total of 103 intestinal samples of broiler chickens, clinically suspected to NE, were obtained from eight organic farms. Samples were collected aseptically in plastic bags in the post-mortem examination of chickens and quickly transported to the laboratory in ice-cooled containers.
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