Sub-Inhibitory Concentrations of Chlorhexidine Induce Resistance to Chlorhexidine and Decrease Antibiotic Susceptibility in Neisseria gonorrhoeae

Abstract

Objectives: Chlorhexidine digluconate (chlorhexidine) and Listerine® mouthwashes are being promoted as alternative treatment options to prevent the emergence of antimicrobial resistance in Neisseria gonorrhoeae. We performed in vitro challenge experiments to assess induction and evolution of resistance to these two mouthwashes and potential cross-resistance to other antimicrobials.Methods: A customized morbidostat was used to subject N. gonorrhoeae reference strain WHO-F to dynamically sustained Listerine® or chlorhexidine pressure for 18 days and 40 days, respectively. Cultures were sampled twice a week and minimal inhibitory concentrations (MICs) of Listerine®, chlorhexidine, ceftriaxone, ciprofloxacin, cefixime and azithromycin were determined using the agar dilution method. Isolates with an increased MIC for Listerine® or chlorhexidine were subjected to whole genome sequencing to track the evolution of resistance.Results: We were unable to increase MICs for Listerine®. Three out of five cultures developed a 10-fold increase in chlorhexidine MIC within 40 days compared to baseline (from 2 to 20 mg/L). Increases in chlorhexidine MIC were positively associated with increases in the MICs of azithromycin and ciprofloxacin. Low-to-higher-level chlorhexidine resistance (2–20 mg/L) was associated with mutations in NorM. Higher-level resistance (20 mg/L) was temporally associated with mutations upstream of the MtrCDE efflux pump repressor (mtrR) and the mlaA gene, part of the maintenance of lipid asymmetry (Mla) system.Conclusion: Exposure to sub-lethal chlorhexidine concentrations may not only enhance resistance to chlorhexidine itself but also cross-resistance to other antibiotics in N. gonorrhoeae. This raises concern regarding the widespread use of chlorhexidine as an oral antiseptic, for example in the field of dentistry.

Biofilm Production by Critical Antibiotic-Resistant Pathogens from an Equine Wound

“…However, a cross-resistance between biocides and antibiotics cannot be overlooked. In fact, several studies and with different strains have shown that subinhibitory concentrations of chlorhexidine induce resistance to chlorhexidine, and decrease susceptibility to antibiotics [ 32 , 33 , 34 ].…”

Efficacy of biofilm disrupters against Candida auris and other Candida species in monomicrobial and polymicrobial biofilms

“…It is important to note that repeated use of CHD at sub-inhibitory concentrations can lead to reduced activity against several pathogens. [49][50][51][52] This has been shown to be due to the development of multidrug efflux pumps which can be expressed in both gram-positive and gram-negative bacteria. 53 Though highly effective against several species of Candida, 54 the broad-spectrum antiseptic CHD has been shown to be less effective against C. auris, which can persist even after twice a day treatment with the antiseptic.…”

“…It is important to note that repeated use of CHD at sub‐inhibitory concentrations can lead to reduced activity against several pathogens 49–52 . This has been shown to be due to the development of multidrug efflux pumps which can be expressed in both gram‐positive and gram‐negative bacteria 53 …”

Maintenance of bacterial outer membrane lipid asymmetry: insight into MlaA

“…The consequences of mlaA mutations in pathogens are diverse. In N. gonorrhoeae mutations in mlaA induced by exposure to sublethal concentrations of chlorhexidine enhances resistance not only to chlorhexidine but also to azithromycin and ciprofloxacin, which is suspected to be a result of cross-resistance [ 96 ]. In E. coli [ 9 ] and S. flexneri [ 97 ], mutations within the vps-mlaA transporter genes result in increased sensitivity to SDS (sodium dodecyl sulphate).…”