Topical antibiotics, antiseptics, can make changes to the skin microbiome that last for days after t

Use of topical antibiotics can significantly alter the skin microbiome and potentially impact the defense against pathogens. While antiseptics also alter this bacterial community, their impact is smaller and not as long-lasting.

These findings are reported online ahead of print in Antimicrobial Agents and Chemotherapy (June 19, 2017).

A press release from the Perelman School of Medicine at the University of Pennsylvania, Philadelphia, where the research was conducted, notes that if the natural ecosystem of harmless and beneficial bacteria on the skin is disturbed or destabilized, colonization or infection by more dangerous microbes can occur. This disruption could occur through the use of antiseptics, such as ethanol or iodine, or through use of topical antibiotics.

“We know antibiotics and antiseptics can be effective in stopping the growth of certain bacteria, but we wanted to know about the larger impact these treatments can have on the resident microbial communities on the skin,” the study’s lead author, Adam J. SanMiguel, PhD, a researcher in the Grice Laboratory at Penn, said in the release.

To learn more about the effect of these anti-microbial agents on the skin microbiome, Dr. SanMiguel and his colleagues treated the skin of hairless mice with a selection of antibiotics, including a narrowly-targeted mupirocin ointment and a broadly applicable triple-antibiotic ointment (TAO) containing bacitracin, neomycin, and polymyxin B. All of the antibiotics changed the makeup of the microbial communities, and, in a key finding of the study, the impact of that change lasted for days after treatment stopped.

“The problem in this case isn’t antibiotic resistance, but instead, how long the disruption of the skin microbiomes continues,” Dr. SanMiguel said. “That disruption opens the door for colonization by an unwanted strain.”

As well, they also evaluated antiseptics – alcohol or povidone-iodine – and compared those treatments with two control groups – mice treated with water and mice entirely untreated.

Neither antiseptic caused responses similar enough to cluster the mice together into groups based on their microbiomes. No clear difference was seen between the treatment groups and the control groups when comparing the relative number of individual bacteria strains.

“We thought antiseptics would be even more disruptive to microbial communities than antibiotics since they are less targeted, but it turns out the opposite is true,” Dr. SanMiguel said. “It shows how stable the skin microbiome can be in the face of stress.”

While variable in scope, both antibiotics and antiseptics were found to decrease colonization by commensal Staphylococcus spp. This effect was highly dependent on baseline levels of Staphylococcus. Since commensal Staphylococcus have been shown to compete with the skin pathogen S. aureus, investigators also tested whether treatment could influence S. aureus levels at the skin surface. They found that the treated mice were more susceptible to carrying S. aureus. Re-introducing the commensal Staphylococcus that had been previously disrupted by treatment could reduce S. aureus levels by over 100 times.

“This gives us a better understanding of how topical antimicrobials affect the skin microbiome and what kind of impact their disturbance can have in the context of pathogenic colonization,” said Elizabeth Grice, PhD, an assistant professor of Dermatology in the Perelman School of Medicine, the study’s senior author. “This helps us anticipate their potential effects.”

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