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University of Baghdad College of Veterinary Medicine Dept. of Vet. Public Health/ Food Hygiene Foodborne Intoxications Foodborne intoxication or food poisoning of microbial origin occurs by inge...

University of Baghdad College of Veterinary Medicine Dept. of Vet. Public Health/ Food Hygiene Foodborne Intoxications Foodborne intoxication or food poisoning of microbial origin occurs by ingesting a food containing a preformed toxin. Two of bacterial origin, staphylococcal intoxication and botulism, and mycotoxicosis of mold origin are briefly discussed in this lecture. The discussions include relative importance of a disease, characteristics of the microorganisms involved, predominant types of food, nature of the toxins, disease and the symptoms, preventative measures, and, for some, analysis of actual outbreak. Some general characteristics of food poisoning are: 1. The toxin is produced by a pathogen while growing in a food. 2. A toxin can be heat labile or heat stable. 3. Ingestion of a food containing active toxin, not viable microbial cells, is necessary for poisoning (except for infant botulism, in which viable spores need to be ingested). 4. Symptoms generally occur quickly, as early as 30 min after ingestion. 5. Symptoms differ with type of toxin; enterotoxins produce gastric symptoms and neurotoxins produce neurological symptoms. 6. Febrile symptom is not present. 1 II. STAPHYLOCOCCAL INTOXICATION A. Importance Staphylococcal food poisoning (staphylococcal gastroenteritis; staphylococcal food poisoning; staph food poisoning), caused by toxins of Staphylococcus aureus, is considered one of the most frequently occurring foodborne diseases worldwide. In the U.S., at least before the 1980s, it was implicated in many outbreaks. However, in recent years, the number of staphylococcal food poisoning outbreaks has declined. CDC reports indicate that during 1972 to 1976, it was associated with 21.4% of the foodborne disease outbreaks ,in contrast, between 1983 and 1987, there were 5.2% staphylococcal foodborne outbreaks ,with no deaths. This decline is probably a reflection of the better use of refrigerated temperatures to store food and improved sanitary practices that can control contamination and growth of Sta. aureus. Even then, the number of outbreaks and number of cases of staphylococcal gastroenteritis is much higher than several other microbial foodborne disease outbreaks. B. Characteristics of Staphylococcus aureus 1. Organisms Sta. aureus are Gram-positive cocci, , and are nonmotile, noncapsular, and nonsporulating. 2. Growth Most strains ferment mannitol and produce coagulase, thermonuclease, and hemolysin, The cells are killed at 66oC in 12 min, and at 72oC in 15 s. Sta. aureus are facultative anaerobes, but grow rapidly under aerobic conditions. They can ferment carbohydrates and also cause proteolysis by extracellular proteolytic enzymes. They are mesophiles with a growth temperature range of 7 to 48oC, with fairly rapid growth between 20 and 37oC. They can grow at relatively low Aw (0.86), low pH (4.8), and high salt and sugar concentrations of 15% and in the presence of NO2. However, their growth can be reduced by combining two or more parameters. 2 Because of their ability to grow under several adverse conditions, Sta. aureus can grow in many foods. Normally, they are poor competitors to many other microorganisms found in foods. But their ability to grow under adverse environments gives them an edge in growth in many foods in which others do not grow favorably. 3. Habitat Enterotoxin-producing Sta. aureus strains have generally been associated with staphylococcal food intoxication. Although strains of several other Staphylococcus species are known to be enterotoxin producers, their involvement in food poisoning is not fully known. Sta. aureus, along with many other staphylococci, are naturally present in the nose, throat, skin, and hair (feathers) of healthy humans, animals, and birds. Sta. aureus can be present in infections, such as cuts in skin and abscesses in humans, animals, and birds, and cuts in hands and facial-erupted acne in humans. Food contamination generally occurs from these sources. C. Toxins and Toxin Production Enterotoxigenic strains of Sta. aureus produce seven different enterotoxins: A, B, C1, C2, C3, D, and E (also designated as SEA, SEB, etc.) They are serologically distinct heat-stable proteins and differ in toxicity. The toxins vary in heat stability, SEB being more stable than SEA. Normal temperature and time used to process or cook foods do not destroy the potency of the toxins. Outbreaks from SEA are more frequent, probably because of its high potency. Rate of toxin production by a strain is directly related to its rate of growth and cell concentrations. Optimum growth occurs at 37 to 40oC. Under optimum conditions of growth, toxins can be detected when a population has reached over a few million per gram or milliliter of food and generally in 4 h. Some of the lowest environmental parameters of toxin production are 10oC, pH 5.0, or Aw 0.86. However, by combining two or more parameters, the lowest ranges can be adversely affected. 3 D. Disease and Symptoms Staphylococcal toxins are enteric toxins and cause gastroenteritis. A healthy adult has to consume 30 g or ml of a food containing 100 to 200 ng toxins produced by 106–10 7 cells/g or /ml; infants and old and sick individuals need lesser amounts. The symptoms occur within 2 to 4 h, with a range of 30 min to 8 h, and are directly related to the potency and amounts of toxin ingested and an individual’s resistance. The disease lasts for 1 to 2 d and is rarely fatal. The primary symptoms, from stimulation of the autonomic nervous system by the toxins, are salivation, nausea and vomiting, abdominal cramps, and diarrhea. Some secondary symptoms are sweating, chills, headache, and dehydration. However, the symptoms and their severity vary among individuals in an outbreak. E. Food Association Many foods have been implicated in staphylococcal foodborne outbreaks. In general, the bacterium grows in the food and produces toxins without adversely affecting the acceptance quality. Many protein-rich foods, foods that are handled extensively, foods in which associated bacteria grow poorly, and foods that have been temperature abused are associated with staphylococcal gastroenteritis. Some of the foods that have been more frequently implicated are corned beef, salami, barbecued meat, salads, baking products containing cream, sauces, and cheeses. baking products, beef, turkey, chicken, and eggs are associated with the high percentages of outbreaks. Different types of food, because of extensive handling and high chance of temperature abuse, have been implicated in relatively high numbers in staphylococcal food poisoning. Three major contributing factors in these outbreaks were improper holding temperature (51.6%), poor personal hygiene (23.4%), and contaminated equipment (17.2%). Major sources of outbreaks (where foods were prepared or served) were food services (24.7%), homes (14.9%), and picnics (8.5%). A high percentage of outbreaks occurred between May and October (63.8%). In the case of imported foods, a raw or processed food exported from a country can have Sta. aureus toxins, but can cause food poisoning in a different country. This is exemplified by at least six outbreaks 4 of staphylococcal gastroenteritis in 1989 in the U.S. from the consumption of dishes prepared by using enterotoxin-containing canned mushrooms processed in a plant in the People's Republic of China. Sta. aureus probably grew before canning and the enterotoxin, being heat-stable, remained potent after canning. F. Prevention (Reduction) of the Disease The normal occurrence of Sta. aureus in raw food materials, among food handlers, and many food environments makes it impossible to produce foods that are free of this bacterium. Thus, a zero tolerance is not economically possible to achieve. Many foods can contain Sta. aureus, and consumption of a food containing 100 or 500 cells/g (or /ml) will, in all probability, not make a person sick (unless the food has large amounts of preformed toxin). To reduce the incidence of staphylococcal food poisoning, the aim is to reduce initial load of Sta. aureus in a food by proper selection of the quality of the raw materials and ingredients, sanitation of the food environments, and proper personal hygiene among food handlers. People with respiratory diseases, acute types of facial acne, skin rash, and cuts in hands should not handle the food. Where possible, products should be heat-treated to ensure killing of live cells. Following heating, recontamination of the products should be avoided. The most important aim is to chill the processed products and ready-to-eat foods to 4oC quickly. Suitable preservatives can also be used to kill or arrest growth. The inside of the food, and not only the surface, should reach the chilled temperature, preferably within 1 h. Finally, the food should not be subjected to temperature abuse and stored for a long period of time at growth temperature before eating. Once heat stable toxins are formed, heating before eating does not ensure safety. H. Analysis of an Outbreak A foodborne disease outbreak affecting 52 of 101 people who attended a dinner (foods prepared at home) was reported on December 6, 1986, in Riverton, WY.9 Of these, 49 needed immediate medical attention. The symptoms developed in less than 1 to 7 h after the meal and included nausea (100%), vomiting (98%), diarrhea (90%), abdominal cramps (83%), prostration (62%), chills (52%), sweating (35%). An 5 investigation revealed that a person who deboned and handled the cooked turkey had an erupting facial rash (acnei form). The turkeys (three total) were improperly cooled following cooking and held on an improperly heated steam table for 4 h before serving. This is a classical case of staphylococcal food poisoning outbreak, in which more than half the people who ate foods involving several preparations developed many of the classical symptoms, some within 30 min. Although the food samples served in the dinner or vomit samples from the attending physicians or medical facilities were not available, analysis of a vomit sample saved by a patient revealed the presence of very high numbers of coagulase-positive Sta. aureus and meat available from a leftover turkey carcass also had fairly large numbers of Sta. aureus. Therefore, from the symptoms and indirect evidence, the outbreak was concluded to be an incidence of staphylococcal food poisoning. The sequences of events were most likely as follows. The erupting facial rash of the food handler was most probably the source of the pathogen. The pathogen was transmitted by the individual through the hands while deboning the cooked turkey. Sta. aureus can grow in meat under a suitable environment. The turkey, following cooking and before serving, was temperature abused for a long period of time, thus enabling the contaminants to grow and reach very high populations. However, the acceptance quality of the meat was not adversely affected. The stage was set and many consumed enough toxin with turkey to develop the symptoms. III. BOTULISM A. Importance Botulism results following consumption of food containing the potent toxin botulin of Clostridium botulinum. It is a neurotoxin and produces neurological symptoms along with some gastric symptoms. Unless prompt treatment is administered, it is quite fatal. Infant botulism occurs when an infant ingests Clo. botulinum spores, which germinate, grow, and produce toxins in the GI tract and cause specific symptoms. 6 B. Characteristics 1. Organisms Cells of Clo. botulinum strains are Gram-positive rods, occur as single cells or in small chains; many are motile, obligate anaerobes, and form single terminal spores. Cells are sensitive to low pH (