Antiseptic residue may promote the emergence of resistant bacteria

An antiseptic substance commonly used to disinfect patients' skin in hospitals can persist on various surfaces for several hours and could contribute to the emergence of bacteria that are tolerant or even resistant to its action, according to a study published in the scientific journal Environmental Science & Technology, cited by Live Science. The research draws attention to a possible unwanted side effect of the intensive use of antiseptics in hospitals: repeated exposure of bacteria to small doses, insufficient to completely destroy them, can promote their adaptation and the development of antimicrobial resistance.

The study, coordinated by Erica Hartmann, professor of civil and environmental engineering at the McCormick School of Engineering and Applied Sciences at Northwestern University, analyzed the behavior of bacteria exposed to chlorhexidine - an antiseptic frequently used before surgeries or when inserting catheters. In the study, scientists collected a total of 219 samples from an intensive care unit of a medical center in the US state of Illinois in 2018, taking samples from: hospital beds; nurse call buttons; window sills; keyboards; switches; sink drains.

Although the rooms were considered clean, the researchers isolated approximately 1,400 bacteria, and 36% of them showed some degree of tolerance to chlorhexidine.

• The antiseptic persists on surfaces even after cleaning

Laboratory experiments showed that traces of chlorhexidine applied to materials such as plastic, metal or laminate remained detectable for at least 24 hours, including after washing the surfaces with water and cleaning agents.

According to the authors, these residues are no longer concentrated enough to destroy bacteria, but create an ideal environment for the selection of more resistant microorganisms.

• How bacterial tolerance occurs

The researchers explain that bacteria repeatedly exposed to low concentrations of antiseptics: are not completely eliminated; begin to chemically adapt to the environment;

develop genes that allow them to survive more easily. In the long term, this tolerance can turn into complete resistance, a situation in which the bacteria are no longer affected even by high concentrations of antiseptics.

One of the most important conclusions of the study is that antiseptic-tolerant bacteria can transfer DNA fragments between themselves that promote resistance not only to antiseptics, but also to antibiotics. Specifically, some of the bacteria analyzed carried plasmids - small circular DNA structures that can be transferred between bacteria - that: promoted tolerance to chlorhexidine; could also contribute to resistance to powerful antibiotics such as carbapenems, considered last-resort treatments.

• Sinks, "hot spots” for resistant bacteria

The study identified hospital sinks as some of the most problematic areas in terms of the development of resistant bacteria. Specialists explain that they provide ideal conditions for the proliferation of microorganisms because: they maintain constant humidity; they concentrate chemical residues; they allow the spread of bacteria through aerosols. Researchers found tolerant bacteria even on window sills and doors, suggesting that they could be dispersed through the air along with fine water particles generated during the use of sinks.

• Experts urge caution, not panic

While the conclusions are important, specialists warn that they do not mean that antiseptics should be abandoned, especially in high-risk medical areas. Danna Gifford, an expert in antimicrobial resistance at the University of Manchester, argues that limiting the use of chlorhexidine in hospitals without further clinical evidence could put patients at risk. However, the research highlights the need for more cautious and better targeted use of antiseptics.

• Soap and water remain sufficient for household use

The authors of the study believe that, in many everyday situations, the use of strong antiseptic products is not necessary. "Simple soap and water are more than enough for cleanliness and hygiene,” stressed Erica Hartmann. Experts warn that antimicrobial resistance is becoming one of the biggest threats to modern medicine. "We are running out of antibiotics that work effectively,” warns Hartmann, emphasizing that without rapid measures, the world could end up in a situation where routine medical procedures, such as treating a tooth infection or performing a simple operation, become extremely risky.