DRUG-RESISTANT SALMONELLA SPREADING, RESEARCHERS WARN

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A bacterium that causes food poisoning has joined the growing list of microbes that are resistant to several different antibiotics, according to a new study.

The existence of multi-drug resistant bacteria poses a danger to public health and-because the microbe in question, salmonella, typically infects animals, not people-steps such as using few er antibiotics on farm animals are necessary, the researchers said.

This form of salmonella, which is resistant to five antibiotics, is related to a strain of the bacterium called typhimurium, which causes about 25 percent of food poisoning attributed to salmonella.

The multi-drug resistant type accounted for just 0.6 percent of the salmonella typhimurium cases in 1979 and 1980, but grew to 34 percent of cases in 1996, according to a team of researchers from the Centers of Disease Control and Prevention (CDC) in Atla nta.

"We estimate that between 68,000 and 340,000 cases of infection with typhimurium with the five drug pattern of resistance...occur naturally in the United States," they reported in this week's issue of The New England Journal of Medicine.

While many cases of food poisoning due to salmonella are short-lived and don't require antibiotic treatment, the increasing spread of this multi-drug resistant type is cause for concern because resistant strains are very difficult to treat, said lead inve stigator M. Kathleen Glynn, a veterinarian with the CDC's Foodborne and Diarrheal Diseases Branch.

Furthermore, finding multi-drug resistant salmonella shows that bacteria in animals can develop drug resistance, and that drug resistance in animal-based bacteria can affect people's health, said Dr. Stuart B. Levy, director of the Center for Adaptive Genetics and Drug Resistance at Tufts University School of Medicine in Boston.

Unlike other drug-resistant infections, such as tuberculosis, salmonella primarily affects livestock such as cattle and chickens. People can become infected if they eat raw eggs, meat that has not been cooked thoroughly or if they use the same surface to cut meat and vegetables, Levy said.

The drug-resistant strains probably have developed because animals are treated with low doses of antibiotics to enhance their growth, as well as to treat more severe infections, he said. While persistent low-dose antibiotics probably are not strong enough to kill all the bacteria present, they can cause some of the "heartier" strains to develop resistance.

The study findings are "a reflection that everywhere antibiotics are being used, they're being misused...and misuse results in infections that are very difficult to treat," Levy pointed out.

In an editorial accompanying the report, Levy called for limiting the use of antibiotics in livestock solely to treating disease, just as health organizations have called on doctors to stop prescribing antibiotics unnecessarily.

The less these antibiotics are used, the less chance there is of a strain developing a resistance to these drugs, he said.

The New England Journal Medicine

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