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Bacteriology at UW-Madison |
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 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. 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, which produces a huge array of invasins and exotoxins, causes wound and surgical infections that lead to gas gangrene, in addition to severe uterine infections. Clostridial hemolysins and extracellular enzymes such as proteases, lipases, collagenase and hyaluronidase, contribute to the invasive process. Clostridium perfringens also produces an enterotoxin and is an important cause of food poisoning. Usually the organism is encountered in improperly sterilized (canned) foods in which endospores have germinated.
OFF THE WALL
Case 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 F (48.8 C), 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 F (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 F-125 F (16 C-52 C). 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 epidemiological 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. Stereotyping is not useful for confirming C. perfringens outbreaks and, in general, is not available.
Corned beef is a popular ethnic dish that is commonly served to celebrate St. Patrick's Day. The errors in preparation of the corned beef in this outbreak were typical of those associated with previously reported foodborne outbreaks of C. perfringens. Improper holding temperatures were a contributing factor in most (97%) C. perfringens outbreaks reported to CDC from 1973 through 1987. To avoid illness caused by this organism, food should be eaten while still hot or reheated to an internal temperature of greater than or equal to 165 F (74 C) before serving.
Clostridium perfringens,
Gram Stain. Most clostridia are renowned for staining "Gram variable".
C. difficile
Clostridium difficile causes antibiotic associated diarrhea (AD) and more serious intestinal conditions such as colitis and pseudo membranous colitis in humans. These conditions generally result from overgrowth of Clostridium difficile in the colon, usually after the normal flora has been disturbed by anti microbial chemotherapy.
People in good health usually do not get C. difficile disease. Individuals who have other conditions that require prolonged use of antibiotics and the elderly are at greater risk of the disease. Also, individuals who have recently undergone gastrointestinal surgery, or have a serious underlying illness, or who are immunocompromised, are at risk.
C. difficile produces two toxins: Toxin A is referred to as an enterotoxin because it causes fluid accumulation in the bowel. Toxin B is an extremely lethal (cytopathic) toxin.
Stool cultures for diagnosis of the bacterium may be complicated by the occurrence and finding of non toxigenic strains of the bacterium, so the most reliable tests involve testing for the presence of the Toxin A and/or Toxin B in the stool. The toxins are very unstable. They degrade at room temperature and may be undetectable within two hours after collection of a stool specimen leading to false negative results of the diagnosis.
In the hospital and nursing home setting, C. difficile infections can be minimized by judicious use of antibiotics, use of contact precautions with patients with known or suspected cases of disease, and by implementation of an effective environmental and disinfection strategy.
Clostridium difficile infections can usually be treated successfully with a 10 day course of antibiotics including metronidiazole or vancomycin (administered orally).
C. difficile colonies
on blood agar
