A new study investigates the role of bacteria and fungi in the human mouth. Researchers from Case Western Reserve University in Cleveland, OH, published their findings in the journal PLOS Pathogens.
Experts know that organisms that live in our mouths are capable of contributing to both health and disease.
It is also known that these organisms are more likely to cause oral diseases, such as oral candidiasis (oral thrush), in people with compromised immune systems - such as those who have cancer or who are infected with HIV.
In this new study, researchers compared the bacteria and fungi present in the mouths of people who are HIV-positive with the bacteria and fungi present in the mouths of healthy people.
The researchers used high-throughput gene sequencing to catalogue the bacteria and fungi present.
They found that there was no overall difference in the bacteria found in people infected with HIV and the healthy people. However, there were consistent differences in the oral fungi present in the two groups.
The Candida family of fungi was found in both groups, but at higher levels in the mouths of people with HIV. Another fungi family, Pichia, was found in high levels in the healthy group, but at lower levels in the group with HIV.
'Good' oral fungi can suppress 'bad' oral fungi
The researchers wondered if the reason for the opposite fungi levels in the two groups was because one species of fungi works to suppress the other.
Fast facts about oral candidiasis
- Symptoms include creamy white lesions, loss of taste and a "cottony feeling" in the mouth.
- Repeated bouts of oral candidiasis could be the first sign of HIV infection.
- In people with HIV, oral thrush is more likely to spread to other parts of the body - such as the lungs, liver and intestines.
To test this, they grew Pichia alone in a liquid and then filtered the fungus out. They found that the "Pichia spent medium" (PSM) that was left was able to stop Candida and several other forms of disease-inducing fungi from growing.
This explains why oral candidiasis (otherwise known as "thrush") is a common complication of HIV infection, despite the fact that antiretroviral therapies have reduced the susceptibility of HIV-infected people to different types of infection.
Translating their findings with the PSM to an animal model, the researchers treated a group of mice with PSM and found that they had much less severe symptoms of oral candidiasis than a group of untreated mice.
"Our findings have wide implications regarding the discovery of novel antifungal agents and will open the way to new therapeutic approaches for the management of fungal infections," the study authors say.
"Detailed investigations are warranted to purify and characterize the specific Pichia factors that can inhibit Candida and other disease-causing fungi," they conclude.