Whether they had clear or pimply skin, all the study participants sported similar abundances of P. acnes living in their pores, but not all of the strains were the same. The researchers found a number of different strains of the microbe, including 66 that had never been identified before. When they sequenced the genomes of each strain and compared them, they discovered that two of the strains, RT4 and RT5, were found predominantly in people with acne—and that one strain, RT6, was found almost exclusively in people with clear skin. Because this "good" strain contains genes known to fight off bacterial viruses and other potentially harmful microbes, the researchers suspect that it may actively ward off the "bad" strains that are associated with disease, thereby keeping skin healthy.
I'm a biologist, so I'll do my best to field any questions.
Edited by PickleShmickle, 28 February 2013 - 10:19 AM.