Toxigenic Potential of Bacillus cereus Strains Isolated from Retail Dairy Products in Egypt

Abstract

Little is known about the virulence in Bacillus cereus strains isolated from retail dairy products in the Middle East and particularly from Egypt. In this study, the occurrence of B. cereus in 290 samples of dairy products (raw milk, Ras cheese, pasteurized extended shelf life [ESL] milk) collected from retail shops was investigated. The potential of 126 selected isolates of B. cereus to possess genes encoding nonhemolytic enterotoxin, hemolysin BL, and cytotoxin K (cytK), and to grow at 7°C was verified. The highest occurrence of B. cereus was found in raw milk (85%, 85/100) followed by Ras cheese (10%, 10/100) and ESL milk samples (8.8%, 8/90). A large proportion of the B. cereus isolates from raw milk (48.9%, 48/99) and Ras cheese (71.4%, 10/14) had at least one complete set of toxin genes (nhe or hbl). Enterotoxin genes, nheA, nheB, nheC, hblA, hblD, and hblC, were detected in 38.4% (5/13), 53.8% (7/13), 61.5% (8/13), 46.1% (6/13), 46.1% (6/13), and 23.1% (3/13) of ESL milk isolates, respectively. cytK was identified in 42.4% (42/99), 50% (7/14), and 46.2% (6/13) of raw milk, Ras cheese, and ESL milk isolates, respectively. The psychrotrophic ability was observed in 22.2% and 15.3% of isolates recovered from raw milk and ESL milk, respectively. The toxigenic potential of B. cereus strains described in this study may pose a health risk to the consumer and, therefore, the presence of these bacteria in retail dairy products should be monitored to ensure consumers' safety.