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Study Highlights Potential Skin Microbiome Role in Infection Risk

NEW YORK (GenomeWeb) – A study appearing online today in mBio suggests components of microbial communities found on the skin can influence an individual's ability to clear bacterial infections.

Researchers from Indiana University and Loyola University in Chicago used 16S ribosomal RNA gene sequencing to track skin microbial community members in upper arm swabs collected from eight individuals before, during, and after exposure to a bacterial species called Haemophilus ducreyi, which causes a sexually transmitted genetic ulcer condition called chancroid in adults as well as skin ulcers in children.

"[P]eople who resolve infections start off with microbiomes that resemble each other," senior author Stanley Spinola, a microbiology and immunology researcher at Indiana University, said in a statement. "People who form abscesses in response to infection have different microbiomes that don't resemble each other pre-infection, but during an infection, they get driven to one composition."

H. ducreyi infections tend to be more common in the developing world, the team noted. And in parts of Africa, Asia, and Latin America, chancroid infections have been implicated in increasing HIV transmission risk. But while some individuals clear chancroid-causing H. ducreyi relatively easily, others have more difficulty getting rid of the bug.

Suspecting that both immune and starting skin microbiome features might have something to do with this difference, the team used 16S ribosomal RNA sequencing to characterize skin microbial community members in swab samples taken over time from eight volunteers inoculated in the arm with Haemophilus ducreyi.

Half of the individuals developed pustules, the researchers explained, while the other half briefly experienced less severe papules before spontaneously resolving the infection.

When the team compared pre-infection microbial community members in skin samples from the four 'resolver' individuals and four 'pustule-forming' individuals, it found features that differed depending on vulnerability to the bug. Among the individuals who efficiently cleared H. ducreyi, for example, the researchers saw skin microbiomes that were quite similar to one another.

Once the potential threat of infection was passed in these individuals, meanwhile, higher-than-usual levels of Actinobacteria and Propionibacterium bacteria marked their skin microbiomes.

On the other hand, individuals who developed skin ulcers after H. ducreyi exposure started out with skin microbiomes that were distinct from one another.

But while they started from very different points, the skin microbiomes from the infection-prone individuals converged into relatively uniform microbial communities after H. ducreyi infection. For example, the team found that these often contained species from genera such as Proteobacteria, Bacteroidetes, Micrococcus, Corynebacterium, Paracoccus, and Staphylococcus.

Even so, the researchers noted that the overall diversity of skin microbiomes was comparable in the infection resolvers and infection-susceptible individuals. And they are still uncertain about why pre-infection skin microbiomes showed such similarities in the resolvers compared to the starting communities in the susceptible group.

"The number one question is whether the microbiome that is present in patients who resolve the infection is merely a signature of an innate immune system that is good at clearing the skin of infections or are there specific bacteria in that composition that are helping the immune system clear the pathogen," Spinola said.

It also remains to be seen whether the shared skin microbiome features found in those who clear infections quickly are actually contributing to the host-defense process. If so, the researchers explained, it may eventually be possible to employ key bacterial species for preventing such infections.

"If the bacteria in the resolvers are actually contributing to the host defense, you could think about using bacteria as a probiotic to help prevent infection or you could use the microbiome to identify people at risk for certain infections," Spinola said.