Clues are emerging that Staphylococcus species may be contributors to acne vulgaris, according to a new study that examined changes in the skin microbiota of acne patients undergoing topical treatment.

Comparing topical antibiotic treatment for acne with a novel cosmetic formulation, Brigitte Dreno, MD, PhD, and her colleagues found that normal skin had fewer surface staphylococci than did skin with comedones or papulopustular eruptions (P = .004 for comedones; P = .003 for papules and pustules). Further, the number of staphylococci increased as acne severity increased (P less than .05 for the increase seen between scores of GEA-2 and GEA-3 on the Global Acne Severity Scale).

These results were seen in a split-face study of 26 adults with mild to moderate acne (GEA-2 and GEA-3) that compared a topical 4% erythromycin gel to a “dermocosmetic” containing lipohydroxy, linoleic, and salicylic acids, niacinamide, piroctone olamine, a ceramide, and water from a thermal spring. Each patient used each product on half of his or her face for 28 consecutive days while avoiding use of other skin care products or topical medications during the study period ( Exp Dermatol. 2017;26[9]:798-803; doi: 10.1111/exd.13296).

Patients’ acne severity was assessed at days 0, 14, and 28 using the GEA scale, together with a count of inflammatory and noninflammatory lesions. The mean GEA grade for patients at enrollment was 2.4. For each patient, skin microbiota samples were obtained from an area with comedones, an area with papulopustular lesions, and an unaffected area.

Dr. Dreno, professor of dermatology at University Hospital, Nantes, France, and her coauthors noted that the range of bacterial diversity was similar on all the facial areas sampled.

After 28 days of treatment, the antibiotic-treated facial skin had significantly less Actinobacteria species, including corynebacteria and propionibacteria. However, the effect on Staphylococci was limited, “potentially confirming the increased resistance of the bacterium to macrolides,” they wrote.

Facial skin treated with the cosmetic, by contrast, had fewer Actinobacteria and fewer Staphylococcus species by the end of the study period, though staphylococci remained the predominant organisms after treatment. Patients saw a significant reduction in both inflammatory and noninflammatory lesions during the study period (P less than .05), with no significant difference between antibiotic- and cosmetic-treated skin.

The authors said that previous studies have shown that propionibacteria are common commensal organisms, representing up to 30% of the bacteria on healthy skin. For the individuals enrolled in the study, though, propionibacteria made up just 2% of the bacteria on the surface of both healthy skin and skin with acne.

Staphylococci, and S. epidermidis in particular, may use fermentation as a defense against other organisms in the skin microbiota. Since staphylococci are aerobic and facultative anaerobic species, they flourish on the skin surface. Propionibacterium acnes, by contrast, is anaerobic, and primarily inhabits the sebaceous follicle.

The complex interplay of skin microbiota contribute to acne and other dermatologic pathology in ways that are just beginning to be understood. “Even though the association between P. acnes and acne vulgaris is well established, very few studies have investigated the entire facial skin microbiota of patients with acne,” wrote Dr. Dreno and her coauthors.

One of the six study authors are employees of L’Oreal; two are employees of La Roche–Posay Dermatological Laboratory, which funded the study and produced the cosmetic product used by the researchers.

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