07 May 2023

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What if chlorhexidine no longer works?

By Arianna Bianchi

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The resistance of bacteria to antibiotics is, unfortunately, a severe problem, estimated to lead to 10 million deaths in 2050. It’s a topic that greatly worries the scientific community and beyond. However, less attention has been given to the resistance of bacteria against antiseptics and biocides, such as chlorhexidine. But in 1980, a study verified the presence of gram-negative bacteria resistant to this active ingredient in patients with long-term bladder catheters.

In dentistry, chlorhexidine is the gold standard antiseptic for plaque control and management of gingivitis and periodontitis. The presence of the outer membrane in gram-negative bacteria can function as a permeability barrier for chlorhexidine and limit its antibacterial efficacy, as has already been hypothesized by several studies.

Materials and methods

When asked whether there are already reasons for concern regarding a greater tolerance or even resistance towards chlorhexidine in bacteria present in the oral cavity, the authors of a study published in Frontiers in Microbiology said that, unfortunately, it is not possible to answer this question so easily.

On the one hand, chlorhexidine is still highly effective in various fields of clinical application, such as the oral health realm. On the other hand, there are studies that confirm the appearance of bacterial species that show greater tolerance towards chlorhexidine.

True resistance to chlorhexidine will have important and serious consequences for infection control.

In the study, the authors point out that low-level exposure to chlorhexidine, potentially occurring in the deepest layers of oral biofilms, can lead to the development of cross-resistance to antibiotics. This could amplify the problem of bacterial resistance to antibiotics. 

For the authors, since currently there is still little awareness of the potential risks that could derive from the widespread and immoderate use of chlorhexidine in dentistry, this research topic should be considered particularly hot, thus leading to the realization of novel studies.

From the authors' point of view there are two key questions related to chlorhexidine resistance that need to be addressed:

Could the widespread use of chlorhexidine lead to an enrichment of resistant strains in oral biofilms and further encourage the development of cross-resistance in them?

What are the molecular mechanisms that confer resistance to chlorhexidine in bacteria present in the oral cavity?

Conclusions

The emergence of resistant bacteria because of the massive use of chlorhexidine in dental practice has not been systematically studied so far. Cultivating bacteria in oral biofilm models and treating them with chlorhexidine sequentially would provide insight into the ecological changes of the oral biofilm microbiota after long-term treatment with this antimicrobial agent.

It will therefore be important to analyze the impact of chlorhexidine by conducting an analysis of the microbiome using high-throughput sequencing methods and culture techniques capable of distinguishing between viable and non-viable cells.

In addition, antibiotic resistance testing can facilitate the study of the potential effects of chlorhexidine on antibiotic cross-resistance and the emergence of multidrug-resistant bacteria.

For more information: "Resistance toward chlorhexidine in oral bacteria - Is there cause for concern?."