A new study finds that tiny pests are carrying plenty of bacteria.

New Yorkers don’t only share the city with 8.5 million other human residents. There’s also a seemingly infinite number of pests, like the house mouse, that can appear on both Park Avenue or Coney Island.

Now new research finds these furry animals carry bacteria that can cause abdominal pain or gastrointestinal distress in humans.

A new study from the Center for Infection and Immunity at Columbia University Mailman School of Public Health published today in the journal mBio has found that New York City mice carry the bacteria responsible for many of the causes of gastroenteritis in humans.

What’s worse is that some of these bacteria appear resistant to common antibiotics.

In previous studies, researchers found that the common house mouse (with the scientific name of Mus musculus) inhabits all areas of the globe except Antarctica. House mice have been known to carry bacteria as they burrow their way into homes.

But this is the first survey to look at house mice, the bacterial strains they carry, and their antibiotic resistance in a large urban center.

The lead author, Simon H. Williams, BSc, and his team found several gastrointestinal disease-causing agents, including Clostridium difficile (C. diff), Shigella, diarrhea-causing Escherichia coli (E. coli), and Salmonella in the 416 mice they captured in New York City.

“From tiny studios to penthouse suites, New York City apartments are continually invaded by house mice,” said Williams in a released statement. “Our study raises the possibility that serious infections — including those resistant to antibiotics — may be passed from these mice to humans, although further research is needed to understand how often this happens, if at all.”

A total of 416 mice were captured across seven sites throughout New York City, including the boroughs of the Bronx, Manhattan, Brooklyn, and Queens. The majority of the mice were captured around building trash compactor rooms at five locations, with the remaining in the kitchen and food storage area of a commercial building and a private single home residence.

The mice were then weighed, checked to see if they were male or female, and measured for length — an indirect measure of age. Samples from the mice were then taken and analyzed for further evaluation.

Salmonella enterica was one of the bacteria found in the mice. It’s the leading cause of food poisoning outbreaks in the United States. Although this bacterium can cause a multitude of syndromes, it’s most commonly associated with typhoid or enterocolitis and diarrhea.

The Centers for Disease Control and Prevention estimate there are approximately 1.2 million cases of salmonella each year in the United States, causing about 23,000 hospitalizations and 450 deaths. Salmonella is traditionally transmitted via the fecal-oral route — mostly with food contaminated with animal feces.

However, this study didn’t find a definitive link between mice carrying bacteria and humans contracting disease.

Some of the bacteria found also demonstrated antimicrobial resistance to two classes of antibiotic medications, meaning they could be harder to treat if they lead to infection.

The samples showed resistance to fluoroquinolones, a family of medication that includes Cipro and Levaquin, as well as beta-lactam drugs. These include medications such as penicillin and Keflex.

Dr. William Schaffner, professor of preventive medicine and infectious diseases at Vanderbilt University Medical Center, said that this study shows “that we share our microbiome, the microbial population that is in us and around us, with our fellow creatures.”

Schaffner said it was worrying that these kinds of antibiotic-resistant bacteria have appeared in animals that aren’t treated with drugs.

“It’s not entirely surprising that if we sample mice, that they would be carrying some of the same germs that we are. And what has raised everyone’s eyebrows is that we don’t go around treating these wild mice with antibiotics,” he said. “They are not fed antibiotics, but they are carrying bacteria that are sometimes resistant to them.”

The study authors believe that additional research needs to be completed to discover the true role of house mice as a potential source of human illness.

“It is quite clear that we humans have created the antibiotics that we are using among ourselves and in and around our food animals. Those antibiotic-resistant bacteria are now capable of spreading to any number of unintended targets,” said Schaffner.

Schaffner said that this study shows how important it is for humans to cut down on unnecessary antibiotic use so that antibiotic-resistant bacteria don’t develop and spread.

“This gives us a sense of how pervasive antibiotic resistance is,” said Schaffner. “When you see the doctor and you have a viral infection, don’t go in expecting an antibiotic prescription, because antibiotics won’t work. Ask what else they can offer to help get over that infection.”

Rajiv Bahl, MD, MBA, MS, is an emergency medicine physician and freelance health writer. You can find him at www.RajivBahlMD.com.