Antibiotics given to the animals that provide the key ingredient for certain kinds of pepperoni or salami may have an unforeseen consequence: weakening helpful bacteria and allowing dangerous ones to thrive.

Fermented sausages are made by inoculating meat with bacteria that produce lactic acid, which kills pathogenic bacteria in the meat. But in a new study, scientists from the University of Copenhagen and University College Cork found that antibiotics commonly given to livestock inhibited the fermentation activity in five of six commercial starter cultures of the helpful bacteria used in sausage making.

The scientists also made experimental sausages inoculated with E. coli or Salmonella bacteria. They found that sausages with antibiotic residue had disruptions in their fermentation process and high levels of the pathogenic bugs, the researchers wrote in a paper appearing in the journal mBio on Tuesday.

"At low concentrations and at regulatory levels set by authorities, we could see that the lactic acid bacteria are more susceptible to the antibiotics than the pathogens are," senior author and University of Copenhagen researcher Hanne Ingmer said in a statement Tuesday. "So basically, we can have a situation where residual antibiotics in the meat can prevent or reduce fermentation by the lactic acid bacteria, but these concentrations do not effect survival or even multiplication of pathogens."

About 80 percent of all antibiotics used in the U.S. are given to farm animals. The federal government has recently moved to restrict this practice, which leads to the development of antibiotic-resistant strains of bacteria that are threats to humans. In April, the U.S. Food and Drug Administration issued a new rule requiring farmers and ranchers to get a prescription for their antibiotics from a veterinarian.

But now add another worry about antibiotics to the list: a higher risk for foodborne illnesses.

"Our work reveals an overlooked risk associated with the presence of veterinary drugs in meat," the authors wrote.

SOURCE: Kjeldgaard et al. "Residual Antibiotics Disrupt Meat Fermentation and Increase Risk of Infection." mBio 3: e00190-12, 28 August 2012.