The newest pathogenic strain of Escherichia coli has been variously associated with fast-food restaurants and supermarket hamburger, but, un- like most new pathogens, it has no catchy nickname. It is known instead by its antigen profile 0 (somatic) type 157 and H (flagellar) type 7.
This bacterium is the agent of a spectrum of conditions, ranging from mild gastroenteritis with fever to bloody diarrhea. About 10% of patients develop hemolytic uremic syndrome (HUS), a severe hemolytic anemia that can cause kidney damage and failure.
The highest risk is to young children and the elderly and to immunocompromised people. Antibiotic treatments do not seem to help, and there is really no prevention other than avoiding ingestion of the pathogen. The first human cases of disease were reported in 1982 and since then have continued to increase, probably due to improved diagnosis. Approximately 4,000 cases a year are reported in the United States, although the actual number is possibly as high as 75,000 cases.
This new strain has acquired a virulence plasmid for production of Shiga (Shigella) toxin that accounts for the more severe disease symptoms. The pathogen originates from the intestine of dairy cattle, and it is transmitted mainly in contaminated beef, water, and fresh vegetables. Hamburger is a common vehicle because meat processing plants tend to grind meats from several sources together, thereby contaminating large amounts of hamburger with meat from one animal carrier. Millions of pounds of hamburger have been recalled from supermarkets because of common source outbreaks.
The largest epidemic in the United States occurred late in 1999, when over 600 people became infected from drinking well water at a fair in New York state. This emerging infection has been an impetus for several changes from the slaughterhouse to the lab to the kitchen. Critics have proposed that the older visual inspection of meat alone is inadequate to detect bac- teria and must be supplemented. The primary way to identify 0157:H7 is through culture on selective media and other special laboratory tests. The extra expense and time involved in such tests would greatly complicate the inspection process and require prolonged storage times. A panel of federal officials has recommended that a rapid chemical test that can detect the microbial load be used on all meat and poultry. A group of Montana researchers has developed a 4-hour test that verifies E. coli in samples by means of fluorescent antibodies.
It is very sensitive and could be supplied in test kits for slaughterhouses, supermarkets, produce suppliers, or even water companies. Another result of this newly recognized food-borne pathogen are those small warning labels that now appear on all fresh meat and poultry Microbits 20.4). One guideline is to bring the meat up to a temperature of at least 155°F (68°C) for a few minutes. That would kill most food-borne pathogens. Certainly, ground beef must be cooked completely through and not consumed when it is still rare or pink. Because of its threat, 0157:H7 was listed as an emerging infectious agent and added to the list of reportable diseases.
Escherichia coli cells glow in a sample of raw ground beef mixed with fluorescent antibodies specific for the pathogen.
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