Just one course of antibiotics is strong enough to disrupt the normal makeup of bacteria in your gut for up to a year — potentially leading to antibiotic resistance and causing other potential health problems.

That’s the upshot of new research published in the journal mBio spotlighting yet another way antibiotic-resistant bacteria arise to pose a threat to public health, Medical News Today reports.

The study — led by Egija Zaura, an associate professor in oral microbial ecology at the Academic Centre for Dentistry in Amsterdam, the Netherlands — examined 66 healthy adults from the U.K. and Sweden who were prescribed different antibiotics.

Participants treated with a single course of one of four antibiotics — ciprofloxacin, clindamycin, amoxicillin or minocycline — were compared to those given an inactive placebo.

Laboratory tests showed the drugs severely affect microbial diversity in the gut for many months after exposure — and up to a year in patients given cipro. In particular, researchers saw a decline in the abundance of health-associated species that produce butyrate — a substance that inhibits inflammation, cancer formation, and stress in the gut.

In addition, the researchers found the antibiotics boosted the activity of genes associated with antibiotic resistance.

Amoxicillin had no significant effect on bacterial diversity, but was associated with the greatest number of antibiotic-resistant genes.

"Antibiotics should only be used when really, really necessary,” said Zaura, summarizing the researchers’ conclusions.

“Even a single antibiotic treatment in healthy individuals contributes to the risk of resistance development and leads to long-lasting detrimental shifts in the gut microbiome. Certainly we cannot live or survive without antibiotics; that's out of the question. But there are situations when we should not use them, like when there are no evidence-based reasons."

Resistant bacteria cause at least 2 million cases of disease and 23,000 fatalities in the U.S. annually. As a result, the Centers for Disease Control and Prevention (CDC) have ranked the top 18 drug-resistant threats and encouraged health to limit the use of antibiotics.

Those in the "urgent" category are:

•    Clostridium difficile (C. difficile), which causes life-threatening diarrhea
•    Carbapenem-resistant Enterobacteriaceae (CRE), mostly occurring in medical facilities, where it causes bloodstream infections that prove fatal in half of cases
•    Neisseria gonorrhoeae that cause gonorrhea, a sexually transmitted disease, affecting 820,000 people a year.