Can Listerine prevent STIs? Researchers want to find out

2017 01 10 17 09 31 816 Mouthwash Man 400

Rinsing with the antiseptic mouthwash Listerine for one minute can significantly reduce the prevalence of gonorrhea-causing bacteria, according to a new study. Now, researchers want to know whether Listerine can also help prevent the spread of sexually transmitted infections (STIs).

In 1879, the manufacturer of Listerine claimed the mouthwash could cure gonorrhea. With gonorrhea infections increasing worldwide, a team of researchers from Melbourne, Australia, thought it was a good time to investigate whether Listerine really does inhibit the growth Neisseria gonorrhoeae in the mouth and throat. The findings of their small study were published in the journal Sexually Transmitted Infections (December 20, 2016).

"If Listerine has an inhibitory effect against N. gonorrhoeae in the pharynx, it could be a cheap, easy to use, and potentially effective intervention for gonorrhea prevention and control," wrote the authors, led by Eric Chow, MPH, PhD. Chow is a senior research fellow at the Melbourne Sexual Health Clinic.

Rinsing once for 1 minute

New gonorrhea cases are on the rise throughout the world, including in the U.S. and Australia. The trend is especially prevalent for men who have sex with men (MSM), and gonorrhea diagnoses among men in Australia doubled over the past five years, according to the study authors.

"If daily use of mouthwash was shown to reduce the duration of untreated infection and/or reduce the probability of acquisition of N. gonorrhoeae, then this readily available, condomless, and low-cost intervention may have very significant public health implications in the control of gonorrhea in MSM," the authors wrote.

“Listerine mouthwash is a cheap, easy-to-use, and effective agent that inhibits gonorrhea growth.”
— Eric Chow, MPH, PhD, and colleagues

To test the effect of Listerine on N. gonorrhoeae, Chow and colleagues recruited 58 men who have sex with men to participate in their randomized clinical trial. The men all tested positive for gonorrhea infections during a checkup at the Melbourne Sexual Health Clinic.

Before they were treated for gonorrhea with conventional methods, the participants rinsed and gargled with either 20 mL of Cool Mint Listerine or a saline solution for one minute. Researchers tested for the presence of N. gonorrhoeaat in the tonsillar fossae and posterior oropharynx before and after the one-minute rinse.

Participants who rinsed and gargled with Listerine showed a significant decrease in the prevalence of gonorrhea in their throats, even after using the antiseptic mouthwash just once for one minute. However, while the decrease was statistically significant in the tonsillar fossae region, it was not in the posterior oropharynx.

Percent of participants who tested positive for N. gonorrhoea after rinsing and gargling
  Listerine Saline p-value
Pharyngeal surface 52% 84% 0.013
Tonsillar fossae 57% 90% 0.016
Posterior oropharynx 57% 70% 0.277

In addition to their clinical trial, the researchers performed an in vitro study in which they tested the effect of Cool Mint Listerine and Total Care Listerine on N. gonorrhoeaecolonies. They also found that both types of Listerine significantly slowed bacterial growth after just one minute.

"The two studies presented here are the first to demonstrate Listerine can inhibit the growth of N. gonorrhoeae in vitro and in a clinical study and raise the potential that it may be useful as a control measure," Chow and colleagues wrote.

Furthering research

The authors acknowledged that the study had a number of shortcomings, including the small sample size. In addition, while it was a randomized trial, neither the participants nor the researchers were blinded to the control and intervention groups.

However, the study results do provide an incentive to continue researching whether antiseptic mouthwashes, such as Listerine, can help prevent the spread of sexually transmitted infections, they noted. The researchers are currently recruiting participants for a follow-up study that will examine whether using Listerine daily for several months reduces the risk of gonorrhea reinfection.

"Our data provide preliminary evidence to support the further investigation of mouthwash as a noncondom-based control measure for gonorrhea," the study authors concluded. "Listerine mouthwash is a cheap, easy-to-use, and effective agent that inhibits gonorrhea growth and requires further careful consideration and study."

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