Acne: Bad and good bacteria identified

A genomic approach to comparing acne-ridden skin with clear human skin has revealed a bacterial strain that may protect against the disease. The work was published online February 28 in the Journal of Investigative Dermatology by Sorel Fitz-Gibbon, PhD, from the Department of Molecular and Medical Pharmacology, Crump Institute for Molecular Imaging, David Geffen School of Medicine, University of California, Los Angeles, and colleagues.

Four of 5 people in the United States develop acne at some point. Although dermatologists no longer blame blemishes on too much chocolate or fatty foods, commonly prescribed acne drugs such as benzoyl peroxide, antibiotics, and isotretinoin (Accutane, Roche) have been used for decades, although they are not ideal. Antibiotics are usually ineffective in severe cases, and isotretinoin both has adverse effects and is teratogenic.

Propionibacterium acnes is a dominant skin commensal that colonizes pilosebaceous units, in which certain strains are hypothesized to stimulate development of acne vulgaris. The population sizes of the bacteria are similar among individuals, but the proportions of different strains vary between people prone to acne and people with clear skin. Similar to Staphylococcus aureus, only certain strains of the bacteria are pathogenic.

The researchers sequenced bacterial genomes to better define the genetic compositions of the P acne component of the skin microbiome in acne-marked vs healthy skin. The strategy revealed "a previously unreported portrait of the microbiota of pilosebaceous units at the bacterial strain level," the researchers write.

Dr. Fitz-Gibbon and colleagues applied over-the-counter pore-cleansing strips to the noses of 49 people with acne and 52 participants with clear skin, sampling P acnes in whiteheads or blackheads. The investigators typed bacterial strains according to 16S ribosomal DNA sequences (ribotypes), assigning each strain an acne index based on prevalence among patients with acne. This approach identified 11,009 ribotypes, but only a few were abundant in either patient group.

Genome sequencing was the next step. Team members from Washington University in St. Louis, Missouri, sequenced the genomes of 66 previously unreported P acnes strains from the samples and compared 71 bacterial genome types overall. Author Shuta Tomida, PhD, also from the Department of Molecular and Medical Pharmacology, Crump Institute for Molecular Imaging, David Geffen School of Medicine, identified DNA differences among the strains.

Beneficial Bacteria

Three genomically identified strains are of potential clinical significance. Two strains were discovered in 1 of 5 volunteers with acne, but rarely in clear-skinned people. Conversely, a third bacterial strain appeared to be common in healthy skin yet was rare in skin with acne, suggesting a protective role.

The findings may have practical applications, the authors write, such as the development of a probiotic topical preparation to favor the protective bacterial strain or drugs to selectively target acne-related bacteria. A simple skin test might predict whether a person has an increased risk of developing aggressive acne.

Further studies might address identifying host factors that contribute to acne and matching microbiome subtypes with clinical subtypes of acne, such as cystic, pustular, or inflammatory acne.

"By combining a metagenomic study of the skin microbiome and genome sequencing of this major skin commensal, this study provides insight into potential bacterial genetic determinants in acne pathogenesis and emphasizes the importance of strain-level analysis of the human microbiome to understand the role of commensals in health and disease," the researchers conclude.

Source: http://www.medscape.com/viewarticle/780020?nlid=28944_1301&src=wnl_edit_dail