Hospital Antiseptics May Be Driving Resistance in Bacteria

A widely used antiseptic to clean hospital patients’ skin can remain on surfaces for hours, creating breeding grounds for bacteria to become tolerant or gain resistance to chemicals that usually kill them, according to a study published in the journal Environmental Science & Technology.

In the study, researchers tracked bacteria with tolerance to chlorhexidine, a chemical applied to patients’ skins before surgery or catheter insertion. They searched for these bacteria in an Illinois medical center’s intensive care unit (ICU), according to Life Science Plus.

Researchers swabbed 219 samples from bedrails, nurse call buttons, door sills, keyboards, light switches, and sink drains in six locations around the ICU in 2018. The rooms were clean, but the researchers isolated about 1,400 bacteria, and 36% showed some tolerance to chlorhexidine.

In the lab, researchers applied chlorhexidine to common materials, such as plastic, metal, and laminate, and tracked how long the antiseptic lingered on surfaces, including after cleaning with water and other chemical cleaners. They found that even after cleaning, traces of the antiseptic persisted on surfaces for at least 24 hours.

These lingering traces weren’t strong enough to kill bacteria. But in these microenvironments, bacteria that carry genes helping them survive the chemical’s effects thrive. These tolerant bacteria outcompete those lacking tolerance genes and grow more abundantly. The worst-case scenario is that bacteria become so used to fighting off a chemical and so good at it that they become resistant to its effects.

The researchers found chlorhexidine-tolerant bacteria throughout the hospital rooms, even though the antiseptic was applied only to patients’ skin. The sink was a hotspot for these bacteria. Swabs also showed tolerant strains on door sills, suggesting they traveled through the air and settled there.

Some of the antiseptic-resistant bacteria carried a plasmid — a small DNA loop that can be transferred between bacteria — that not only helped them tolerate chlorhexidine but could also help them resist antibiotics, such as carbapenems. This type of gene transfer is a well-known way that bacteria gain resistance to antimicrobials, and it can take place between bacteria of totally different species.

Still, chlorhexidine is highly effective at killing germs. The bacteria in the study could survive only at very low concentrations of the chemical, far below levels used to clean patients’ skin. However, the researchers agreed that the world should be more cautious in using antiseptics. Further studies should examine whether these effects occur in other settings, such as homes or veterinary clinics, to better understand how antiseptic residues affect bacteria, the researchers said.