MICROBIOLOGY

• Previously termed Propionibacterium
  • Major human pathogens: There are many species, but generally, the two below represent the majority of isolates. They are members of the Proprionibacteriaeceae.
    
    • Cutibacterium acnes
    • Cutibacterium avidum (less common)
• A Gram-positive pleomorphic rod that grows best anaerobically [Fig].
• Usually inhabits human skin, sebaceous glands, nasopharynx, and GI/GU tracts.
• Generally sensitive to beta-lactams and resistant to aminoglycosides.
• Slow growth, often >5-6d.
  • Incubation time may require up to 14d to recover clinically significant isolates from prosthetic joint infections.
• The reclassification of Propionibacterium species, as described initially, is due to the bacteria producing propionic acid as a fermentation product. Bacteria are seen in various conditions, including cheeses (Swiss), ruminants, stomachs, and human skin. Based on 16s ribosomal analysis, this is now divided into the following:
  • Acidipropionibacterium gen. nov.
  • Cutibacterium gen. nov.
  • Pseudopropionibacterium gen. nov.
  • Propionibacterium (amended description of the genus)
  • Fun Fact: P. freudenreichii is responsible for flavor and characteristic holes during Swiss cheese manufacture.
• C. acnes antimicrobial resistance:
  • Information is mainly gleaned from isolates in refractory cases of acne vulgaris, so the correlation with the much less common systemic or deep infections is unclear.
  • The following are the resistance rates (approximately): erythromycin (50%), clindamycin (35%), and tetracycline (25%).
  • Erythromycin and clindamycin resistance often occur in tandem.
  • Tetracycline is often used if the disease breaks through erythromycin or clindamycin therapy.
  • Minocycline may still have an effect when either tetracycline or doxycycline-resistant strains of P. acnes are suspected.