020217 Drug-Resistant Bacteria in Pigs Spread to People

New York - Researchers in Taiwan are reporting that people are being infected with a strain of Salmonella enterica that is resistant to a family of potent antibiotics known as fluoroquinolones.

"Our data strongly suggest that the inappropriate use of fluoroquinolones in animal feeds is the cause of the emergence in Taiwan of the resistance in Salmonella (enterica) serotype choleraesuis," said Dr. Cheng-Hsun Chiu of Chang Gung Children's Hospital in Taoyuan.

"The use of fluoroquinolones in food animals, therefore, should be prohibited immediately," he said.

Many experts worldwide believe widespread antibiotic use by livestock farmers is one reason why germs are becoming increasingly resistant to the drugs. Since the mid-1990s, when farmers started using fluoroquinolones to fight infections in farm animals used for food including poultry and pigs, researchers have seen the drugs become less powerful against bacteria that cause food-borne illness in humans.

Trouble starts when bacteria become resistant to an antibiotic due to repeated exposure. Humans then pick up the resistant bacteria when they eat or handle contaminated meat.

"We found, for the first time in the world, S. enterica serotype choleraesuis were resistant to a group of antibiotics, (called) fluoroquinolones," Chiu said.

"S. enterica serotype choleraesuis is, among more than 2,000 salmonella serotypes, most virulent to humans," he said. "It usually causes sepsis and other systemic infections in humans.

"Ciprofloxacin (a fluoroquinolone) is one of the drugs usually used for the treatment of such infections--it is very worrisome when the bacteria (develop) resistance to these agents," he added.

Chiu and colleagues analyzed 501 S. enterica serotype choleraesuis samples collected from infected patients between 1987 and 2000.

Prior to 1991, the researchers report, resistance to any antibiotic was generally low--less than 40%. But since then, resistance to many commonly used antibiotics has substantially increased, they write in the February 7th issue of The New England Journal of Medicine.

While there were no reports of resistance to ciprofloxacin through 1999, the authors note that "since March 2000, a dramatic and rapid increase in the incidence of ciprofloxacin resistance in S. enterica serotype choleraesuis has been observed."

While all of the samples of the bug collected from humans in 1997 were susceptible to ciprofloxacin, nearly half of the isolates collected in 2000 and 2001 were resistant to the drug, the team reports.

The investigators also conducted an extensive DNA analysis of S. enterica serotype choleraesuis samples taken from both humans and pigs. They determined that pigs were the "primary source" of the resistant germ.

"This investigation in Taiwan indicates that fluoroquinolone-resistant S. enterica serotype choleraesuis can spread from swine to humans," Chiu and colleagues write.

"The use of fluoroquinolones in food animals should be prohibited," they conclude.

While antimicrobial resistance of S. enterica serotype choleraesuis has been increasing, Chiu pointed out that his team's report is the first to describe resistance in this important human pathogen to an antibiotic that is critical to human medicine.

"The emergence of fluoroquinolone resistance has changed our treatment policy to choleraesuis infections," Chiu said. "Because the majority of choleraesuis isolates are also resistant to conventional antibiotics--such as ampicillin, chloramphenicol and trimethoprim-sulfamethoxazole--the third generation cephalosporins now become the only antibiotics with reliable activity for the treatment of choleraesuis infections in Taiwan."

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