Toxin genes and cytotoxicity levels detected in Bacillus cereus isolates collected from cooked food products delivered by Swiss Army catering facilities

Heated food is known to be often contaminated with B. cereus, leading to cases of diarrhoeal or emetic diseases. Battalion kitchens or army catering facilities present a food safety risk, as temperature abuse and long storage time can result in serious public health problems affecting a high number of served people. In contrast to civil catering facilities, no microbiological monitoring systems are currently implemented in Swiss military kitchens. In this study toxin gene profiles and cytotoxicity levels of 21 isolates of B. cereus originating from six different food categories were determined. Nearly all isolates (95%) harbored the nhe gene, whereas no hbl could be detected. Seven isolates displayed the cytK2 gene and one cereulide-producer was isolated out of vegetables. While most isolates displayed low cytotoxicity, highly cytotoxic strains were detected, with three isolates even exceeding the cytotoxicity level of the reference strain for high-level toxin production, underpinning that cytotoxicity cannot be deduced only from presence or absence of toxin genes. These findings further underline the importance of rapid cooling of foods or maintenance over 65°C before serving. This is especially important in mass catering facilities, such as military kitchens, in which food is often prepared a long time in advance.