Bacteria have the ability to combine and increase infectiousness

Lawrence Goodwyn

When bacteria join forces, it isn’t good news.

UT biologists recently discovered that two species of mouth bacteria often found together, Aggregatibacter actinomycetemcomitans, also known as Aa, and Streptococcus gordonii, also known as Strep can combine to make an Aa infection grow faster.

Apollo Stacy, UT microbiology graduate research assistant and lead author of this study, said that strep provides Aa with the oxygen and nutrients it needs to grow through a process the scientists have called, “cross-respiration.” Biologists have known about a similar term, “cross-feeding,” which occurs when a bacteria provides another bacteria with the food it needs to grow. But Stacy said that “cross-respiration” is unique in that it provides another bacteria with oxygen as well.

Molecular biology professor Marvin Whiteley said that a waste-product of strep, L-lactate, is a prime food source for the Aa bacteria.

“Strep essentially gives Aa its favorite food and the utensils to eat it with,” Whiteley said.

Stacy said that the two bacteria species can be found together in people’s mouths and in abscesses in the lungs or brain.

In extreme cases of Aa bacteria can lead to periodontal disease, rotting teeth in a matter of weeks. Additionally, a person can develop endocarditis, an infection of the heart valves due to the infection seeping into the bloodstream.

“You see it [Aa] in the gums of relatively young people, causing periodontal disease, and outside the body in abscesses that appear like a pimple,” Whiteley said.

But on its own, Whiteley said the species of strep bacteria is fairly harmless.

“Strep gordonii is located on the surface of your teeth and it’s commensal, meaning it is noninfectious, and nearly every person on the planet has it,” Whiteley said.

According to Stacy, only certain genes in the strep bacteria have the ability to make Aa more infectious. He has been working on isolating which genes actually lead to infection.

“You would always think that more bacteria is always worse, and actually that’s not true, it’s specific pairs of genes inside the bacterias that cause infection, not the amount of bacteria,” Whiteley said.

The team plans to continue researching this pair of bacteria and possibly expand it to new pairs too. Stacy said he would like to see how Aa interacts with other bacteria. The team hopes their research might lead to a new way of fighting disease.

“When we think about treating infections we think about fighting the pathogen—if you have a staph infection—kill the staph. But many bacterias acquire antibiotic resistance and are hard to kill,” Whitley said. “Now we’re starting to think, what if you kill the partner bacteria that’s feeding it, then maybe that would be a new way to treat infections”