A single course of antibiotics is strong enough to disrupt the normal makeup of microorganisms in the gut for up to a year, potentially leading to antibiotic resistance, says research published in mBio.

Share on Pinterest Antibiotics are increasingly unable to fight bacteria as resistance develops.

For 70 years, antimicrobial agents, known as antibiotics, have been successfully fighting infectious diseases, dramatically reducing rates of illness and death worldwide.

However, their widespread use has led to adaptations in the infectious organisms that they are designed to kill, reducing the drugs’ effectiveness.

In the US, antibiotic-resistant bacteria cause at least 2 million cases of disease and 23,000 fatalities annually.

As a result, the Centers for Disease Control and Prevention (CDC) have outlined the top 18 drug-resistant threats to the US and categorized them based on level of concern: urgent, serious or concerning. Health professionals have been encouraged to limit the use of antibiotics.

Those in the “urgent” category are currently:

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 almost 50% of cases

Neisseria gonorrhoeae that cause gonorrhea, a sexually transmitted disease, affecting 820,000 people a year.

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

Participants were randomly assigned to receive a full course of one of four antibiotics: ciprofloxacin, clindamycin, amoxicillin or minocycline, or a placebo.

The researchers collected fecal and saliva samples from participants at the start of the study, immediately after taking the antibiotics, and 1, 2, 4 and 12 months after finishing the course.