Propionibacterium species are part of the normal bacterial flora that colonize the skin, conjunctiva, oropharynx, and gastrointestinal tract. These non-spore-forming, anaerobic, gram-positive bacilli are frequent contaminants of specimens of blood and other sterile body fluids and have been generally considered to play little or no pathogenic role in humans.
Propionibacterium acnes and other Propionibacterium species have, however, been recovered with or without other aerobic or anaerobic organisms as etiologic agents of multiple infection sites. These include conjunctivitis, intracranial abscesses, mycotic aneurysm, peritonitis, and dental, parotid, pulmonary, and other serious infections. They have often been recovered as a sole isolate in specimens obtained from patients with infections associated with a foreign body (such as joint infection, an artificial valve), endocarditis, and central nervous system shunt and post surgical intracranial infections. Some P. acnes strains possess synergistic capabilities with facultative and aerobic bacteria. The possible role of P. acnes in the pathogenesis of acne vulgaris was suggested. The data that support this are based on the recovery of this organism in large numbers from sebaceous follicles, especially in patients with acne, on its ability to elaborate enzymes such as lipase, protease, and hyaluronidase, and on its ability to activate the complement system and enhance chemotactic activity of neutrophils.
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