Antiseptic mouthwash against pharyngeal Neisseria gonorrhoeae: a randomised controlled trial and an in vitro study

BackgroundGonorrhoea is increasing among men who have sex with men (MSM). We aimed to determine whether Listerine, a commercial mouthwash product, has an inhibitory effect against Neisseria gonorrhoeaein a randomised controlled trial (RCT) and an in vitro study, and therefore may be a potentially useful agent for gonorrhoea control.MethodsIn vitro: a suspension of ∼108colony forming units per mL (CFU/mL) of N. gonorrhoeaewas added to a serial of dilutions (up to 1:32) of alcohol-containing Listerine mouthwashes (Cool Mint and Total Care) for 1 min. A 10 µL aliquot was spread over the surface of a gonococcal agar plate and the number of N. gonorrhoeaecolonies present at each dilution was calculated. The phosphate buffered saline (PBS) was used as a control. RCT: we recruited MSM with pharyngeal gonorrhoea who returned for treatment at the Melbourne Sexual Health Centre between May 2015 and February 2016. Untreated men were randomised to rinse and gargle either Listerine Cool Mint or saline for 1 min. Pharyngeal swabs were taken before and after rinsing and gargling for culture of N. gonorrhoeae. The analysis included only men who were culture positive for N. gonorrhoeaebefore using the allocated solution on the day of recruitment.ResultsIn vitro: Listerine mouthwashes at dilutions of up to 1:4 for 1 min resulted in significant reduction of total N. gonorrhoeaecounts but PBS has no inhibitory effect against N. gonorrhoeae. RCT: a total of 196 MSM were recruited, 58 (30%) were culture positive before using the solution. After gargling the allocated solution, men in the Listerine group were significantly less likely to be culture positive on the pharyngeal surface (52%) compared with men in the saline group (84%) (p=0.013).ConclusionsThis data suggest Listerine, significantly reduces the amount of N. gonorrhoeaeon the pharyngeal surface. With daily use it may increase gonococcal clearance and have important implications for prevention strategies.Trial registration numberACTRN12615000716561.