The mouthwash can help curb the growth of the bacteria responsible for gonorrhoea, researchers said.
New cases of gonorrhoea among men are on the rise in many countries amid declining condom use, with the bulk of cases among gay/bisexual men, they said.
Rising rates of gonorrhoea heighten the risk of the emergence of antibiotic resistant strains of Neisseria gonnorhoeae, the bacteria responsible for the infection, making the need for a preventive measure that does not rely on condoms even more urgent, researchers said.
Now, the researchers, including those from Melbourne Sexual Health Centre in Australia, assessed whether Listerine could curb the growth of N gonorrhoeae in laboratory tests and in sexually active gay/bisexual men in a clinical trial.
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For the laboratory tests, different dilutions (up to 1:32) of Listerine Cool Mint and Total Care, both of which contain 21.6 per cent alcohol, were applied to cultures of N gonorrhoeae to see which of any of them might curb growth of the bacteria.
Listerine at dilutions of up to 1 in 4, applied for one minute, significantly reduced the number of N gonorrhoeae on the culture plates, whereas the saline solution did not.
The clinical trial involved 196 gay/bisexual men who had previously tested positive for gonorrhoea in their mouths/throat, and who were returning for treatment at one sexual health clinic in Australia, between May 2015 and February 2016.
Almost a third (30 per cent) tested positive for the bacteria in their throat on the return visit.
After rinsing and gargling for one minute, the proportion of viable gonorrhoea in the throat was 52 per cent among the men using Listerine compared with 84 per cent among those using saline.
The men using Listerine were 80 per cent less likely to test positive for gonorrhoea in their throat five minutes after gargling than were the men using the saline solution.
The researchers admit that the monitoring period was short, so the possibility that the effects of the mouthwash might be short-lived can not be ruled out.
The study was published in the journal Sexually Transmitted Infections.