Mouthwash may kill gonorrhea bacteria

The bacteria that cause gonorrhea can be found in a person's throat, but stopping the growth of these germs may be as simple as gargling with mouthwash, a small new study from Australia finds.

The idea that mouthwash could kill certain strains of bacteria is not new — in fact, as far back as 1879, Listerine advertised that it could "cure" gonorrhea, according to the new study.

But in the hundred-plus years since the company made the claim, no scientific studies have tried to assess it, the authors wrote in their new study, which was published Dec. 20 in the journal Sexually Transmitted Infections.

The rates of gonorrhea , which is caused by the bacteria Neisseria gonorrhoeae, have more than doubled in men in Australia over the past five years, the researchers, led Eric Chow, a research fellow at the Melbourne Sexual Health Centre in Australia, wrote in the study. About 70 percent of the cases are in men who are sexually active with other men , the researchers added.

In the U.S., gonorrhea rates have also increased in recent years, according to statistics from the Centers for Disease Control and Prevention. In 2014, there were 110.7 cases per 100,000 people, which was a 5.1 percent increase over the 2013 rate, and a 10.5 percent increase over the 2010 rate, according to the CDC.

It's unclear if fighting gonorrhea that's found in people's throats could also reduce the rates of gonorrhea infections in other parts of the body, such as the urethra, the researchers wrote. However, previous studies have suggested that an infection in the throat appears to be a source of urethral and anal infections, according to the study.

To test whether Listerine could indeed kill off N. gonorrhoeae, the researchers carried out two experiments.

In the first experiment, the researchers tested whether two Listerine products, Cool Mint and Total Care, could stop the growth of the bacteria in petri dishes. They chose these two Listerine products because they contained alcohol, which the researchers hypothesized would inhibit the growth of the bacteria, according to the study.

The Listerine products were tested in various dilutions, and the researchers found that a one-to-four ratio of either Listerine product to water was sufficient to significantly halt the growth of the bacteria after one minute.

The researchers also looked at the effects of Listerine in 58 men who tested positive for gonorrhea in their throats. The men were either given Listerine Cool Mint or a saltwater solution and asked to rinse and gargle for one minute. Five minutes later, the researchers retested the men's throats for gonorrhea.

They found that the men who gargled with Listerine were 80 percent less likely to test positive for gonorrhea than those who were given the saltwater solution.

But the location of the infection in the throat appeared to play a role in how well the Listerine worked: The mouthwash was much more effective at killing bacteria on the tonsils than bacteria farther down in the throat, according to the study.

"It may be that more mouthwash reaches the [tonsils] than the [back of the throat] during use and highlight[s] the need to gargle and not just rinse," the researchers wrote.

The researchers noted that the study was small, and larger studies are needed to confirm the results. In addition, because the researchers retested the men only 5 minutes after they used the mouthwash, it's unclear if the mouthwash had a short-lived effect. Further studies should look at the effects of daily mouthwash use, the researchers wrote.

Originally published on Live Science .