Food Protection Trends - February 2009 - 86

species are of both public health and economic concern in the food processing industry. B. cereus is well-established as a significant cause of foodborne illness in humans. The possible contribution of other Bacillus species than B. cereus in food poisoning has, however, not been fully established. The Bacillus cereus group consists of five different closely related species (excluding B. anthracis), and at least two of those species can cause food poisoning. B. cereus is widespread in nature, and frequently isolated from soil and growing plants. From its natural environment it is easily spread to foods, where it may cause an emetic or a diarrhoeal type of food-associated illness that is becoming increasingly important in the industrialized world. The emetic disease is a food intoxication caused by cereulide, a small ring-formed dodecadepsipeptide. The diarrhoeal syndrome of B. cereus is an infection caused by vegetative cells, ingested as viable cells or spores, thought to produce protein enterotoxins in the small intestine. Three pore-forming cytotoxins have been associated with diarrhoeal disease: Hemolysin Bl (Hbl), Nonhaemolytic enterotoxin (Nhe) and Cytotoxin k. Three other species: Bacillus subtilis, B. licheniformis and B. pumilus have also been involved in food poisoning. Duration and range of symptoms are similar to that caused by B. cereus, however the incubation period and symptoms vary between and within species suggesting that other toxins than the well known B. cereus enterotoxins are involved. Similar small ring formed peptides with fatty acid tails have been shown to be produced by about 5% of strains of these species. These peptides are also toxic to several different cell types and are most probably the reason for the food poisoning symptoms caused by these strains. Clostridium mIkE PECk, Institute of Food Research, Norwich research Park, Colney, Norwich, Nr4 7UA, Uk The two most significant foodborne pathogenic clostridia are Clostridium perfringens and Clostridium botulinum. Both are Gram-positive endospore-forming anaerobes. Clostridium perfringens is a frequent cause of foodborne disease in many countries. For example, it is the second most common cause of both illness and associated death in England and Wales (84,081 cases of diarrhoea and 89 deaths estimated in 2000), while in the USA it is estimated to be the fourth most frequently identified cause of bacterial-associated foodborne illness (248,500 cases of diarrhoea per year). C. perfringens is associated with food poisoning when cooked foods are not cooled correctly, permitting spore germination and subsequent rapid multiplication of emerged vegetative cells between 40°C and 50°C to an infectious dose. The presence of large numbers of vegetative cells in the gut and associated production of enterotoxin can lead to illness. Clostridium botulinum is responsible for foodborne botulism, an intoxication in which the bacterium grows and forms a highly potent neurotoxin in food. Botulinum neurotoxin is the most potent substance known (as little as 30–100 ng can be fatal), and consumption of pre-formed botulinum can lead to botulism, a severe (but rare) disease with a high fatality rate. The ability to form botulinum neurotoxin is restricted to C. botulinum and some strains of C. baratii and C. butyricum. C. botulinum is not a homogeneous species, but a collection of four physiologically and genetically distinct bacteria, with the name “C. botulinum” retained to emphasise the importance of neurotoxin formation. There are seven major botulinum neurotoxins (types A to G). Staphylococcus CyRIL SMyTH, Dept. of Microbiology, Moyne Institute of Preventive Medicine, Trinity College Dublin, University of Dublin, Dublin 2, Ireland Staphylococcal food poisoning (SFP) is a foodborne toxinosis caused by heat-stable, protease-resistant enterotoxins released during growth of S. aureus on food. Affected persons experience severe nausea, projectile vomiting, convulsive retching, abdominal cramps and sometimes diarrhoea, usually within 2–8 hours of ingesting the contaminated food. Food with high protein content that requires considerable handling during preparation or merely adequate heating afterwards is commonly incriminated. Some staphylococcal food poisoning outbreaks have involved very large numbers of people – 14,870 cases (low fat milk, osaka, Japan, 2000), ~4,000 cases (chicken–roast beef–rice, minas Gerais, Brazil, 1998), 1,364 cases (deboned chicken salad, Texas, USA, 1992), 862 cases (grilled salmon, Shiga Prefecture, Japan, 2005), and 485 cases (éclairs, Thailand, 1990). To date, 20 staphylococcal enterotoxins (SEs) and enterotoxin-like proteins (SEls) have been described. In addition, three SEs and four SEls have variant isoforms. Estimates of the dose of enterotoxin required to induce emesis vary from 20–100 ng to micrograms. Progress in understanding the mechanism of action of enterotoxins has been made in recent years. SEA has been demonstrated to induce 5-hydroxytryptamine (5-HT) release in the intestine, rather than in brain, and the 5-HT3 receptors on vagal afferent neurons are essential for SEA-stimulated emesis. The role of strains possessing newer SE or SEl genotypes in SFP needs evaluation, given their frequent isolation from nasal carriers. The acceptance of animal models other than monkeys would aid such evaluation. The use of reverse transcriptase PCR to assay expression of SE and SEl genes could provide an effective means of assessing levels of enterotoxin production. 86 FOOD PROTECTION TRENDS | FEBRUARY 2009

Food Protection Trends - February 2009

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