Detection of NHE Complex Genes in Bacillus cereus Isolated from Rice Samples from Zanjan, Iran by Multiplex PCR

Bacillus cereus (B. cereus) is a gram-positive, spore-forming bacteria widely distributed in the environment. This bacteria is an opportunistic human pathogen that can cause diarrheal and emetic types of food poisoning. The diarrhea type of food poisoning can be caused by hemolysin BL (HBL), non-hemolytic (NHE), and cytotoxin K enterotoxins. Rice is commonly contaminated with B. cereus. The objective of this study is to detect enterotoxigenic genes of the NHE complex and assess their incidence in B. cereus isolates in rice samples from Zanjan, Iran. We randomly purchased 10 different rice samples from food stores and cultured them in PEMPA. Following biochemical testing, the bacterial colonies were identified by PCR. B. cereus isolates were checked for the NHE complex genes by specific primers using multiplex PCR. Results showed that rice samples were contaminated with B. cereus. The NHE complex genes were found in 8 bacterial samples. B. cereus is able to tolerate high temperatures; in cooked rice the spores can undergo germination by reheating. The results of this study have shown that NHE multiplex PCR is a prompt, reliable method for the differentiation between non-enterotoxigenic and enterotoxigenic isolates of B. cereus. Despite its common dietary role, rice in Iran has rarely been investigated from a microbiological point of view. Enhancing awareness about virulence and prevalence of genes involved in food poisoning would be effective in the prevention of food poisoning.