Researchers find new, drug-resistant strain of salmonella

Doctors at the Centers for Disease Control and Prevention are worried about a strain of salmonella that resists all but one antibiotic

In this story:

• DT104 emerged in past 10 years
• Antibiotics in animal feed blamed
• Strain resistant to 7 European antibiotics

May 6, 1998
Web posted at: 6:30 p.m. EDT (2230 GMT)

ATLANTA (CNN) -- Researchers report that a dangerous new strain of salmonella has emerged in the past decade that infects thousands of people each year and does not respond to most antibiotics.

According to their study, reported in Thursday's New England Journal of Medicine, laboratories across the United States found that the new strain of salmonella is resistant to five common antibiotics, and responds to only one.

"What we found ... is that a particular organism, which has a kind of unwieldy name -- salmonella typhimurium, or DT104 -- is resistant to five common antimicrobial agents and has emerged right in front of our eyes in about the past 10 years," said Dr. Kathleen Glynn of the Centers for Disease Control and Prevention in Atlanta.

Using data from three sources, Glynn and her colleagues estimated the resistant bacteria were infecting between 68,000 and 340,000 people of the estimated 4 million people infected with salmonella each year.

Salmonella infections kill about 500 people annually.

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Most people recover from the illness on their own, researchers say, but they found that if the illness became severe and medication were needed, most of the antibiotics would be ineffective against DT 104.

DT 104 does respond to one type of antibiotic called fluroquinolines, but researchers worry that it, too, might develop a resistance to fluroquinolines.

"We want to make sure that the agents that are useful in treating this illness today are also useful in treating this illness a year from now," Glynn said.

The low levels of antibiotics in animal feed give bacteria in some animals a chance to develop resistance

Antibiotics in animal feed blamed

Salmonella is caused by eating contaminated food and is characterized by sharp stomach pains, fever and diarrhea that usually lasts from two to five days.

Ordinarily, salmonella infections are not considered serious, but if one becomes severe, antibiotics can save a person's life.

Researchers have warned for more than a decade that the practice of speeding animal growth by adding common antibiotics to livestock food was fostering the evolution of drug-resistant bacteria, but it is still common today.

More than 16 million of the 50 million pounds of antibiotics produced in the United States each year are combined with animal food so the animals will grow faster.

In the United Kingdom "DT104 now appears to be widely distributed in food animals, particularly cattle, and investigations have associated infections in humans with eating pork sausages, chicken and meat paste, and with contact with sick animals," the researchers said.

Antibiotics can save a patient's life

Strain resists 7 European antibiotics

The low levels of antibiotics in animal feed give bacteria in the animals a chance to develop resistance. And once bacteria develop a resistance to one antibiotic, they rapidly learn to resist others as well, said Dr. Stuart B. Levy of Tufts University School of Medicine in an editorial accompanying the report.

"The DT104 strain, whose frequency is rising in the United States, has been plaguing animals and people in Europe for the past decade," Levy said. "There, the organism has acquired resistance to seven drugs that are used to combat it."

Last year, an expert panel of the World Health Organization repeated the call for a ban on the use of human antibiotics to promote the growth of livestock. The group also called for careful use of antibiotics to stop diseases in food animals.

"We need to minimize the environmental impact of antibiotics," Levy said.

He said doctors should stop giving them to humans who have viral infections, for which the drugs are ineffective anyway, and their use in animals should be limited.

The researchers also called for "prudent use of microbial agents in farm animals."

Correspondent Elizabeth Cohen and Reuters contributed to this report.

Related stories:

• Washing produce helps prevent food poisoning - April 30, 1998
• Company recalling beef after E. coli discovery - April 29, 1998
• New California law cooks up raw controversy - March 28, 1998

Related sites:

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• Centers for Disease Control and Prevention Home Page
• New England Journal of Medicine On-line -- Home Page
• Tufts University School of Medicine

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