Antidepressants linked to antibiotic resistance: E. coli study

The widespread use of antibiotics has long been implicated in the rise of drug-resistant infections. Now, scientists wonder whether unrelated drugs play a role too.

In a new study, antidepressants — designed to regulate the brain chemistry of patients with mental illness — were also linked to Escherichia coli (E. coli) antibiotic resistance.

Researchers reported that when E. coli bacteria were exposed to commonly prescribed antidepressants, including fluoxetine (Prozac) and escitalopram (Lexapro), they developed a resistance to many forms of antibiotics.

While some E. coli can be harmless, some strains of infection are sure to prompt uncomfortable abdominal symptoms, such as diarrhea and vomiting.

The study, conducted by researchers at the University of Queensland in Australia, exposed one E. coli strain, MG1655, to five of these commonly prescribed antidepressants and tested their strength against six different types of antibiotics.

Lead author Jianhua Guo, a researcher at the Australian Centre for Water and Environmental Biotechnology, told The Post it’s too early to declare that individuals on antidepressants are more susceptible to infection of E. coli or other harmful bacteria, but their study does open the door to the possibility that drugs labeled for anything but killing bacteria may also be inadvertently contributing to antibiotic resistance.

“Although we mainly used E. coli as a model strain, we would assume these findings apply to other harmful bacteria,” said Guo.

Among the estimated tens of millions of patients on antidepressants globally, the typical daily dosage for people taking antidepressants ranges from about 20-450 mg/day. Some of these medications circulate through the body faster than others, which also means some of these drugs accumulate in larger concentrations in the body than others.

Researchers covered a range of concentrations to reflect this broad scope. A concentration of up to 1 mg/L was considered low level, the medium level was set to 10 mg/L and anywhere between 50-100 mg/L was deemed a high level concentration.

Their arsenal included six classes of antibiotics — beta [β] -lactams (penicillin derivatives), phenicols (e.g., Chloramphenicol), fluoroquinolones (e.g., Levaquin, Cipro), macrolides (e.g., azithromycin, erythromycin), aminoglycosides (e.g., gentamicin, tobramycin) and tetracyclines (e.g., Minocycline, Doxycycline) — all of which attack bacteria in different ways, whether by inhibiting DNA, protein or cell wall synthesis.

The E. coli bacteria cultures were observed over a 60-day period, ample time to account for antibiotic activity, or lack thereof, at any level of antidepressant concentration.

Their findings, published in the Proceedings of the National Academy of Sciences, showed that even low levels of antidepressants circulating through the body could prompt a resistance response to multiple types of antibiotics. The study reported that sertraline, also known as Zoloft, and duloxetine, commonly known as Cymbalta, precipitated the highest number of resistant cells compared to total cells.

“Even after a few days’ exposure, bacteria develop drug resistance, not only against one but multiple antibiotics,” Guo told Nature.

Antibiotic resistance is a growing problem in medicine, making some infections increasingly difficult to treat. In 2019, an estimated 1.2 million people around the world died as a direct result of infections that refused to be treated by traditional means. This resistance happens when germs such as bacteria and fungi are able to overcome the drugs that are supposed to kill them, according to the Centers for Disease Control and Prevention.

The authors call antibiotic resistance a “major threat” to people’s health around the world; however, they noted that it’s unclear just how much these medications are contributing to this phenomenon.

Researchers have suggested that antidepressants may trigger changes in the gut, which has a direct impact on the body’s immune activity. “The gut microbiota for those patients who regularly use antidepressants might have been shifted and disturbed due to antibiotic-like effects of antidepressants, likely affecting their gut health,” Guo told The Post. “We need to pay more attention to it.”