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The clostridia are ancient organisms that live in virtually all of the anaerobic habitats of nature where organic compounds are present, including soils, aquatic sediments and the intestinal tracts of animals.

Clostridia are able to ferment a wide variety of organic compounds. They produce end products such as butyric acid, acetic acid, butanol and acetone, and large amounts of gas (CO₂ and H₂) during fermentation of sugars. A variety of foul smelling compounds are formed during the fermentation of amino acids and fatty acids. The clostridia also produce a wide variety of extracellular enzymes to degrade large biological molecules (e.g. proteins, lipids, collagen, cellulose, etc.) in the environment into fermentable components. Hence, the clostridia play an important role in nature in biodegradation and the carbon cycle. In anaerobic clostridial infections, these enzymes play a role in invasion and pathology.

Most of the clostridia are saprophytes, but a few are pathogenic for humans, primarily Clostridium perfringens, C. difficile, C. tetani and C. botulinum. Those that are pathogens have primarily a saprophytic existence in nature and, in a sense, are opportunistic pathogens. Clostridium tetani and Clostridium botulinum produce the most potent biological toxins known to affect humans. As pathogens of tetanus and food-borne botulism, they owe their virulence almost entirely to their toxigenicity. Other clostridia, however, are highly invasive under certain circumstances.

Clostridium perfringens is classified into 5 types (A�E) on the basis of its ability to produce one or more of the major lethal toxins, alpha, beta, epsilon and iota (α, β, ε, and ι). Enterotoxin (CPE)-producing (cpe+) C. perfringens type A is reported continuously as one of the most common food poisoning agents worldwide. An increasing number of reports also implicate the organism in 5%�15% of antibiotic�associated diarrhea (AAD) and sporadic diarrhea (SD) cases in humans, as well as diarrhea cases in animals.

Most food poisoning strains studied carry cpe in their chromosomes; isolates from AAD and SD cases bear cpe in a plasmid. Why C. perfringens strains with cpe located on chromosomes or plasmids cause different diseases has not been satisfactorily explained. However, the relatively greater heat resistance of the strains with chromosomally located cpe is a plausible explanation for these strains' survival in cooked food, thus causing instances of food poisonings. The presence of C. perfringens strains with chromosomally located cpe in 1.4% of American retail food indicates that these strains have an access to the food chain, although sources and routes of contamination are unclear.

An explanation for the strong association between C. perfringens strains with plasmid-located cpe and cases of AAD and SD disease may be in vivo transfer of the cpe plasmid to C. perfringens strains of the normal intestinal microbiota. Thus, a small amount of ingested cpe+ C. perfringens would act as an infectious agent and transfer the cpe plasmid to cpe� C. perfringens strains of the normal microbiota. Conjugative transfer of the cpe plasmid has been demonstrated in vitro, but no data exist on horizontal gene transfer of cpe in vivo, and whether cpe+ strains that cause AAD and SD are resident in the gastrointestinal tract or acquired before onset of the disease is unknown.

Case Study

Report of C. perfringens Food Poisoning

Clostridium perfringens is a common cause of outbreaks of foodborne illness in the United States, especially outbreaks in which cooked beef is the implicated source. This is a condensed version of an MMWR report that describes an outbreak of C. perfringens gastroenteritis following St. Patrick's Day meals of corned beef. The report typifies outbreaks of C. perfringens food poisoning.

Report
On March 18, 1993, the Cleveland City Health Department received telephone calls from 15 persons who became ill after eating  corned beef purchased from one delicatessen. After a local newspaper article publicized this problem, 156 persons contacted the health department to report onset of diarrheal illness within 48 hours of eating food from the delicatessen on March 16 or March 17. Symptoms included abdominal cramps (88%) and vomiting (13%); no persons were hospitalized. The median incubation period was 12 hours (range: 2-48 hours). Of the 156 persons reporting illness, 144 (92%) reported having eaten corned beef; 20 (13%), pickles; 12 (8%), potato salad; and 11 (7%), roast beef.

In anticipation of a large demand for corned beef on St. Patrick's Day (March 17), the delicatessen had purchased 1400 pounds of raw, salt-cured product. Beginning March 12, portions of the corned beef were boiled for 3 hours at the delicatessen, allowed to cool at room temperature, and refrigerated. On March 16 and 17, the portions were removed from the refrigerator, held in a warmer at 120^oF (48.8^oC), and sliced and served. Corned beef sandwiches also were made for catering to several groups on March 17; these sandwiches were held at room temperature from 11 a.m. until they were eaten throughout the afternoon.

Cultures of two of three samples of leftover corned beef obtained from the delicatessen yielded greater than or equal to 10⁵ colonies of C. perfringens per gram.

Following the outbreak, public health officials recommended to the delicatessen that meat not served immediately after cooking be divided into small pieces, placed in shallow pans and chilled rapidly on ice before refrigerating, and that cooked meat be reheated immediately before serving to an internal temperature of greater than or equal to 165^oF (74 C).

Analysis
C. perfringens is a ubiquitous, anaerobic, Gram-positive, spore-forming bacillus and a frequent contaminant of meat and poultry. C. perfringens food poisoning is characterized by onset of abdominal cramps and diarrhea 8-16 hours after eating contaminated meat or poultry. By sporulating, this organism can survive high temperatures during initial cooking; the spores germinate during cooling of the food, and vegetative forms of the organism multiply if the food is subsequently held at temperatures of 60-125^oF (16-52^oC). If served without adequate reheating, live vegetative forms of C. perfringens may be ingested. The bacteria then elaborate the enterotoxin that causes the characteristic symptoms of diarrhea and abdominal cramping.

Laboratory confirmation of C. perfringens foodborne outbreaks requires quantitative cultures of implicated food or stool from ill persons. This outbreak was confirmed by the recovery of greater than or equal to 10⁵  organisms per gram of epidemiologically implicated food. An alternate criterion is that cultures of stool samples from persons affected yield greater than or equal to 10⁶ colonies per gram. Stool cultures were not done in this outbreak.  Serotyping is not useful for confirming C. perfringens outbreaks and, in general, is not available.

Clostridium perfringens produces many different toxins, four of which (alpha, beta, epsilon, iota) can cause potentially deadly syndromes. The toxins cause damage to tissues, blood cells, and blood vessels.

Gas gangrene is marked by a high fever, brownish pus, gas bubbles under the skin, skin discoloration, and a foul odor. It is the rarest form of gangrene, and only 1,000 to 3,000 cases occur in the United States each year. It can be fatal if not treated immediately.