What problems does the food industry have with the spore-forming pathogens Bacillus cereus and Clostridium perfringens?

Abstract

Spore-forming bacteria are special problems for the food industry. It is not always possible to apply enough heat during food processing to kill spores, thus we have to take advantage of knowledge of the spore-formers to control them. For the meat industry Clostridium perfringens might become a special problem, although this bacterium mainly causes food poisoning through food served in restaurants, hospitals or homes for elderly people (Cliver, 1987; Reynolds, 1987; Gondrosen et al., 1990). The reason for the food poisoning is always the same: meat-containing dishes stored after cooking with insufficient cooling and reheating (Granum, 1990). Even though it should be relatively easy to control this kind of food poisoning, C. perfringens is still one of the most common sources of foodborne diseases. Proper disinfection is necessary to control this type of food poisoning, as it is now clear that only kitchen strains of C. perfringens are able to produce the large amounts of enterotoxin necessary to cause food poisoning (Granum, 1990; Cornillot et al., 1995). Bacillus cereus is more difficult to control, specifically in the dairy industry, where it is now causing the main problems. Insufficient heating of rice-containing dishes has been known to cause B. cereus food poisoning of the emetic kind for a long time (Kramer and Gilbert, 1989), but will not be dealt with in this paper. There are several reasons for the problems in the dairy industry. First of all it seems to be impossible to completely avoid the presence of B. cereus in all milk samples. Secondly the spores are very hydrophobic (Husmark, 1993), and will attach to the surfaces of the pipelines of the dairy industry, where they might multiply and resporulate. A third problem is that pasteurisation heating is insufficient to kill the spores, while competition from other vegetative bacteria is eliminated. It seems that several B. cereus strains have become psychrotrophic over the years, making possible growth at temperatures as low as 4-6 degrees C (Granum et al., 1993a). None of the methods used to control hygiene in the dairy industry so far are able to control B. cereus. This is a continuously increasing problem for the industry but, with emerging knowledge, we should be able to control it. In this paper we will discuss the problems the food industry is facing with C. perfringens and B. cereus, and how these problems might be solved. We will also give our view on how research might ease these problems in the future.