How antidepressants promote bacterial resistance to antibacterial drugs

A team of researchers at the University of Queensland has discovered some of the mechanisms involved when bacteria become more resistant to antibacterial drugs after exposure to antidepressant drugs. In their paper published in Proceedings of the National Academy of Sciences, the group describes the effects of 13 antibiotics after exposure to five kinds of antidepressants.

Back in 2014, one of the researchers, Jianhua Guoa, noticed that bacteria in domestic wastewater appeared to be developing resistance to antibacterial drugs faster than bacteria in hospital wastewater. The finding appeared to be wrong because logic suggested more antibiotics would be taken by people in hospitals than in the general community.

The finding suggested that something besides antibacterial drugs was driving resistance. Then, in 2018, he and a group of his colleagues at the University of Queensland began testing possibilities looking for the culprit. They discovered it was the large amounts of antidepressant drugs being consumed by people in their homes. In this new effort, the same team took a closer look at the means by which such resistance may be developing, hoping to better understand why it happens.

By exposing large numbers of bacteria to large numbers of antidepressants, the researchers found that when antidepressant drugs were placed in a vessel containing bacteria bred in highly oxygenated environments, the chemicals pushed the bacteria to create reactive oxygen-specific species—molecules that activate bacterial defense systems.

Such systems are the same ones used by the bacteria as they develop resistance to antibacterial drugs. Also activated was the bacterial efflux pump system, which is the system used by most bacteria to expel undesirable molecules, such as those found in antibiotic drugs.

The researchers also found that exposure to some antidepressants caused E. coli to increase its mutation rate, which speeds up the process of developing resistance. They also found that it led to selection of genes related to resistance, putting them on the path to becoming fully resistant. And finally, the team found that one type of antidepressant, when exposed to some bacteria, instigated gene transfer between cells, another mechanism for developing resistance.

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