P. acnes Susceptibility and link to Hemolysis

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John K. Crane, MD, PhD " Propionibacterium: beyond Gruyere cheese and acne of the skin to invasive infections” Propionibacterium is one of the most common bacteria that people have never heard of. But Propionibacterium was one of the most abundant microbes found on people’s cellular telephones in the Cell Phone Microbiome project https://microbiomejournal.biomedcentral.com/articles/10.1186/s40168-015-0082-9. Propionibacterium is also an important microbe in the making of Gruyere cheese, also known as Swiss cheese in the United States. The tangy flavor of the cheese, as well as its characteristic holes, come from the propionic acid produced by these bacteria. At cheese-making temperatures the propionic acid is released as a gas, producing the holes. In medical microbiology, Propionibacterium acnes is known as one of the main causes of acne of the skin. In our study, we did not attempt to make cheese, or to study acne, but focused on P. acnes in sites within the human body that are normally sterile, such as blood and internal organs and tissues. P. acnes is an anaerobe, meaning an organism that only grows in the absence of oxygen. Unfortunately for physicians, anaerobic bacteria are usually not tested in the microbiology laboratory for susceptibility or resistance to antibiotics. The reason for this is that anaerobes can take a long time to grow, and even after growth is noted, it can be a labor-intensive process to determine which antibiotics they are sensitive to. Laboratory medicine, including medical microbiology, is one of the areas of healthcare where people are sensitive to costs of care, unlike other areas of medicine where people seem to behave as if cost is no object. As a result, testing for antibiotic susceptibilities is not routinely done on anaerobic pathogens. Our article may help to fill in the knowledge gap, because we tested 106 P. acnes strains for susceptibility to 5 antibiotics. An unexpected finding of our work was that resistance to one antibiotic, clindamycin, was more common in P. acnes strains that showed hemolysis on blood agar. Hemolysis occurs when the bacteria release a toxin or enzyme that lyses the red blood cells in the agar, resulting in a clear area around each colony. One conclusion of our research is that doctors should use caution about using clindamycin for serious P. acnes infections, especially if the strain is hemolytic. To test if hemolysis itself caused the increase in resistance, we had to turn to an old friend from our strain collection, Aeromonas hydrophila, which produces a potent hemolysin. The Aeromonas came from a leech that my daughter collected from a local creek when she was 12 years old. She recently reminded me of a poem by William Wordsworth called “The Leech-Gatherer” which I commend to readers: http://www.online-literature.com/wordsworth/516/ This poem Is also known by the alternative title “Resolution and Independence”. Resolution and Independence are attributes that every researcher needs.

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