Antibiotics can increase spread, severity of Salmonella infections

(NaturalNews) In some cases, treating people or animals with antibiotics may cause them to spread Salmonella infections more rapidly, and even in some cases to develop more severe infections. This may be more likely to occur in those who are not showing any current symptoms of salmonellosis but are receiving antibiotics for some other reason.

The findings came from a study conducted by researchers from Stanford University and published online in the Proceedings of the National Academy of Sciences on October 20.

The research focused on Salmonella typhimurium, which is responsible for approximately 1 million cases of food poisoning in the United States each year, leading to 19,000 hospitalizations and almost 400 deaths. Researchers have known for some time that 70 to 90 percent of people infected with this Salmonella species are not particularly contagious, shedding only small amounts of the bacteria in their feces. The other 10-30 percent, in contrast, are known as "superspreaders" and shed copious amounts of live bacteria.

Notably, superspreaders almost never develop any symptoms of the disease but are responsible for nearly all of its spread.

Antibiotics make mice sicker

The study was conducted on mice, which contract and spread Salmonella easily.

"Mice in a barn can be infected with salmonella for a long time and not get sick," senior author Denise Monack said. "They run around perfectly healthy. They're happy little incubators for salmonella."

Prior research by Monack and colleagues had established that about 20 percent of the mice used in their lab are superspreaders.

"The mice we use are inbred," she said. "So this difference in response to salmonella infection can't be just a simple matter of genetic mutations."

In a prior study, the researchers found that, when mice were given antibiotics, a die-off of their beneficial gut microbes led to a dramatic increase in Salmonella shedding. In the new study, the researchers again treated Salmonella-infected mice with antibiotics. They found that the non-superspreaders abruptly began shedding high levels of the bacteria and showed a huge surge of levels in their guts. Within days, all these mice became sick.

"They lost weight, had ruffled fur and hunched up the in corners of their cages," Monack said. "They also began to shed much larger quantities of bacteria."

The superspreaders, in contrast, appeared unaffected by the antibiotics entirely. They neither became sick nor increased or decreased their rate of Salmonella shedding. Indeed, gut concentrations of Salmonella in the non-superspreaders soon surpassed the concentration in the superspreaders following antibiotic treatment.

The study was conducted with two separate antibiotics -- streptomycin and neomycin -- with the same results seen in both cases.

Are livestock antibiotics causing food poisoning?

In addition to its implications for health screening and treatment, the study may be yet another warning about the risks of widespread prophylactic and growth-promoting use of antibiotics in livestock.

"We humans shouldn't take antibiotics lightly," Monack said. "We need to consider whether they're always beneficial when they're given to animals across the board, or when we take them ourselves."

Approximately 80 percent of U.S. antibiotic use is for growth promotion in healthy livestock.

"We've shown that the immune state of an infected mouse given antibiotics can dictate how sick that mouse gets and also carries implications for disease transmission," Monack said. "If this holds true for livestock as well -- and I think it will -- it would have obvious public health implications. 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."

Sources:

https://med.stanford.edu

http://www.pnas.org

http://medicalxpress.com