Tuesday, November 8, 2016

What bugs are in the skin of normal folks? Do Propionibacterium keep the bad bugs out?

Propionibacterium acnes strain populations in the human skin microbiome associated with acne.

These authors compared the skin microbiome at the strain level and genome level of Propionibacterium acnes between 49 acne patients and 52 healthy individuals by sampling the pilosebaceous units on their noses.  Among the 101 subjects, 59 were female (31 acne patients and 28
normal subjects) and 42 were male (18 acne patients and 24 normal subjects). The average age of the acne cohort was 22.2, and the average age of the normal cohort was 29.6. The authors did not sort the results by sex.

Metagenomic analysis demonstrated that although the relative abundances of P. acnes were similar, 

the strain population structures were significantly different in the two cohorts (RT refers to the ribotype).
Certain strains were highly associated with acne, and other strains were enriched in healthy skin. By sequencing 66 previously unreported P. acnes strains and comparing 71 P. acnes genomes, they identified potential genetic determinants of various P. acnes strains in association with acne or health. 

Their analysis suggests that acquired DNA sequences and bacterial immune elements may have roles in determining virulence properties of P. acnes strains, and some could be future targets for therapeutic interventions. This study demonstrates a previously unreported paradigm of commensal strain populations that could explain the pathogenesis of human diseases. It underscores the importance of strain-level analysis of the human microbiome to define the role of commensals in health and disease.

Comment: These results show that Propionibacterium 'rules the skin' in the oily skin of young persons, whether or not they have acne. What is striking is the absence of Staph aureus and Strep species from the skin microbiome of these subjects, suggesting the possibility that the resident bacteria may have a 'probiotic' effect. Also of note is the fact that the normal skin flora  (Propionibacterium Acnes, Propionibacterium humerusii, Propionibacterium granulosum and Staph Epidermidis and Staph Capitis) have all been recovered from deep cultures of shoulders having revision of failed arthroplasty. These observations leave us with the question "is it a good idea to remove the Propionibacterium from the local skin of candidates for shoulder arthroplasty?"