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Antibiotic therapy for acne was linked with variations in the skin microbiota, some of which persisted and weren't necessarily healthy, a four-patient longitudinal study indicated.

Relative abundance of Cutibacterium acnes decreased 1.4-fold with 4 weeks of minocycline therapy (difference -10.3%, 95% CI −19.9% to −0.7%; P=0.04) in the four participants, women age 25-35. But other bacteria increased, including a transient 5.6-fold rise in the relative abundance of Pseudomonas species, reported Luis A. Garza, MD, PhD, of Johns Hopkins School of Medicine in Baltimore, and colleagues in .

And, in the eight weeks following antibiotic therapy withdrawal, there was a 4.7-fold decline in the relative abundance of Lactobacillus species as well as a 1.7-fold increase in the relative abundance of Streptococcus species, the researchers reported. Abundance of C. acnes partially rebounded as well after minocycline was stopped, such that it was no longer statistically lower than at baseline.

The tetracycline group of antibiotics, including doxycycline and minocycline, often serves as first-line therapy for moderate to severe acne because of these agents' anti-inflammatory and antimicrobial properties. Recent guidelines suggest restricting systemic antibiotic therapy to 3 to 4 months. However, prior respective studies have shown that the antibiotic treatment period always exceeds the recommended duration, noted Garza's group.

"Given the widespread use of systemic antibiotics for acne, it is important to understand their effects not only on C. acnes but also on the complete bacterial community of the skin," they wrote. "Understanding the associations between antibiotics and skin microbiota may help clinicians decrease the likelihood of skin comorbidities related to microbial dysbiosis."

Recently introduced tools for studying the skin microbiome -- including the genome and metabolome -- have "invigorated" studies on their relation to disease and human health and "illuminated the diversity of microorganisms inhabiting the skin surface," noted Tiffany Scharschmidt, MD, of University of California San Francisco, in an .

Amid so much media attention on these studies, patients have become more interested in the human microbiome as well, noted Scharschmidt.

"In the clinic, this interest manifests as a wide range of patient inquiries regarding the role of microorganisms in skin disease, the influence of prescribed therapies on the microbiome, and strategies or products to 'optimize' skin flora for health or cosmesis. Satisfactory answers to these questions are still forthcoming and will likely prove highly nuanced based on the complexity and contextuality of the skin-microbiota relationship," she wrote.

Clinicians should be enthusiastic about the possibility of microbial-directed or microbial-derived treatments "as future weapons in our therapeutic arsenal while acknowledging that there is much we still do not understand about the influence of current therapies on the delicate symbiosis we maintain with our cutaneous microbiota," the editorialist emphasized.

"In the context of a growing market of over-the counter products designed to "restore" the skin microbiome, we should further emphasize that there is no universally good or bad skin microbiome," she continued.

Scharschmidt noted the tiny sample size and other limitations in the study by Garza and colleagues, but nevertheless called the findings "intriguing" and could explain some of the complications often seen from antibiotic therapy in acne.

For their part, Garza and colleagues characterized the study as a pilot investigation. They recruited the four patients in Maryland, who included two white women, one Asian American and one African American. They presented with inflammatory and comedonal acne on the face and reported no recent use of topical or systemic therapy for acne such as retinoids or antibiotics.

Patients were prescribed 100 mg of oral minocycline to take twice daily for 4 weeks. The skin on the forehead, cheek, and chin were sampled for 165 ribosomal RNA gene sequencing at baseline, 4 weeks after starting the antibiotic therapy, and then 1 week and 8 weeks after treatment ended.

Garza, speaking to MedPage Today, acknowledged that the study was too small and too short to offer definitive conclusions. "We only looked a short period of time after antibiotics, but people need to look much longer, like even a year, after somebody stops taking antibiotics," he said.

In their JAMA Dermatology paper, his group also noted that there was no clear, single pattern connecting changes in participants' skin microbiome to changes in acne lesions, perhaps also a consequence of the small sample size.

"The use of a larger sample size and longer duration of antibiotic treatment would enable better characterization of changes in inflamed lesion count and α diversity, which may respond differently to antibiotic treatment depending on acne severity at baseline," they wrote. "Longitudinal data of negative control participants receiving no antibiotic treatment, which we did not collect in the present study, would also enable more accurate characterization of the changes in skin microbiota associated with antibiotic treatment."