Antibiotics: Salmonella’s BFF?

Upfront is a quick look at the latest developments from Stanford Medicine.

About 80 percent of all antibiotics used in the United States are given to livestock because doing so increases the animals’ growth rates. Experts worry that this practice contributes to the rise of drug-resistant pathogens. But a new study, published in the Proceedings of the National Academy of Sciences, highlights a different concern.

When Denise Monack, PhD, associate professor of microbiology and immunology, and her colleagues gave antibiotics to mice infected with the food-poisoning bacterium Salmonella typhimurium, a small minority — so-called “superspreaders” — that had been shedding high numbers of salmonella in their feces for weeks remained blithely asymptomatic. The rest of the mice got sicker instead of better and, oddly, started shedding like the superspreaders. The findings pose ominous questions about the widespread, routine use of sub-therapeutic doses of antibiotics in livestock.

“If this holds true for livestock as well — and I think it will — it would have obvious public health implications,” says Monack. “We need to think about the possibility that we’re not only selecting for antibiotic-resistant microbes, but also impairing the health of our livestock and increasing the spread of contagious pathogens among them and us.”

The concern here is that antibiotic use in livestock will encourage, rather than impede, salmonella’s spread in the animals (and through them, us) while sparing the superspreaders among them (and us) who are responsible for most of its transmission. 

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