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.
Highlights
The ongoing emergence of antimicrobial resistance (AMR) in Neisseria gonorrhoeae has motivated research into antibioticsparing treatment options to treat this pathogen (Chow et al, 2021; Van Dijck et al, 2021b)
Two large randomized controlled trials have found that the regular use of Listerine R in men having sex with men does not reduce the incidence of N. gonorrhoeae or other STIs (Chow et al, 2021; Van Dijck et al, 2021b)
We exposed N. gonorrhoeae reference strain WHO-F to increasing concentrations of Listerine Cool Mint R (Johnson & Johnson, New Brunswick, NH, United States) and Corsodyl containing chlorhexidine (Supplementary Material 1) using a continuous-culture device known as a morbidostat (Toprak et al, 2013; Verhoeven et al, 2019)
Summary
The ongoing emergence of antimicrobial resistance (AMR) in Neisseria gonorrhoeae has motivated research into antibioticsparing treatment options to treat this pathogen (Chow et al, 2021; Van Dijck et al, 2021b). Listerine Cool Mint R ( termed Listerine R ) is a bactericidal mouthwash containing three essential oils [eucalyptol (0.092%); menthol (0.042%) and thymol (0.064%)], methyl salicylate (0.060%) and ethanol (21.6%) (Supplementary Material 1). It exerts its bactericidal effect via a number of pathways, including disruption of the cytoplasmic membranes (Faleiro, 2011; Nazzaro et al, 2013). At least one group of authors have claimed that Listerine does not induce resistance to essential oils but provided little experimental evidence to back this claim up (Hughes and Dean, 2016)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
