Toxin gene pattern in Bacillus cereus group strains isolated from sheep ricotta cheese

Milk and milk whey products processed at high temperatures and then stored by chilling are particularly sensitive to the health risks associated with microorganisms of the Bacillus cereus group (Heyndrickx and Scheldeman 2002). Sheep ricotta cheese is often contaminated by these spore forming microorganisms and it provides a substrate in which they can develop (Corona et al. 2002). B. cereus may cause diarrhoeic or emetic food poisoning outbreaks. Diarrhoeic syndrome is mainly due to HBL and NHE enterotoxins produced when the micro-organisms multiply in the small intestine (Granum and Lund 1997; Hansen and Hendriksen 2001). Emetic syndrome is caused by emetic toxins or cereulide, a dodecapeptide produced when the microorganisms multiply in the food (Kramer and Gilbert 1989; Agata et al. 1996). Their pathogenic profile is also characterized by the ability to produce enterotoxin T, which shows toxic activity only in vitro (Agata et al. 1995), and cytotoxin K, which is necrotizing and hemolytic. Sporadic cases of death from food poisoning have been attributed to cytotoxin K producing strains (Lund et al. 2000). These microorganisms also produce hemolysins (cereolysins, hemolysin II, sphingomyelinases) and different phospholipases C (PIH, PCH and SM) (Granum 1994; Beecher and Wong 2000). The present work reports the molecular profile of the pathogenicity factors of “B. cereus” group strains isolated from fresh and ripened sheep ricotta-cheese. The ability of these strains to produce the hemolytic fraction L2 of HBL and the fraction A of NHE was also tested.