CHICAGO-A research from Washington University School of Medicine in St. Louis found that isotretinoin that has been prescribed to treat acne for decades can shift the skin microbiome of acne patients to more closely resemble that of people with normal skin.

The researchers studied bacteria sampled from facial skin swabs at four time points over the course of the 10-month study. The samples came from 17 patients whose acne was treated with isotretinoin and, as a comparison, eight untreated subjects. Of these eight, four had normal skin and four had acne.

The researchers found that isotretinoin therapy increased the diversity of microbes found on the skin. Through DNA sequencing, the researchers also identified four types of bacteria that bloomed with isotretinoin treatment. None had previously been associated with improved acne.

Isotretinoin also reduced the overall number of Propionibacterium bacteria, even as the treatment increased the diversity of the individual types of this bacteria.

The 38 percent of isotretinoin-treated patients who did not show this beneficial pattern in the Propionibacterium communities is similar to the proportion of isotretinoin-treated patients in other studies who ended up needing additional rounds of therapy. The findings suggest that isotretinoin creates a "bottleneck" that selects for beneficial communities of Propionibacteria and other bacteria that appear to be healthy, thus creating a skin microbial community that reduces the chances of the acne returning even when normal oil production returns to the skin after treatment stops.

"We see this happening here. After the treatment, the microbial communities shift to a mix of populations that appears to be healthier, and that shift persists months after the treatment," said Makedonka Mitreva, the study's senior author and an assistant director of the McDonnell Genome Institute at Washington University School of Medicine.

The researchers said it is important to understand how isotretinoin works, in an effort to create new therapies that might be more effective or have fewer side effects.

Since isotretinoin is known for causing birth defects, it should not be prescribed to women who are pregnant or trying to become pregnant. Women of reproductive age who take isotretinoin are prescribed birth control for the same reason.