MICROBIOLOGY

• Previously termed Propionibacterium
  • Major human pathogens: many species; generally the two below represent the majority of isolates. Member of Proprionibacteriaeceae.
    
    • Cutibacterium acnes
    • Cutibacterium avidum
• A Gram-positive pleomorphic rod that grows best anaerobically [Fig].
• Usually inhabits human skin, sebaceous glands, nasopharynx, 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, for example.
• Reclassification of Propionibacterium species as originally described due to the bacteria producing propionic acid as a fermentation product. Bacteria are seen in a wide range of conditions: including cheeses (Swiss), ruminants stomachs, 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: related P. freudenreichii is responsible for both flavor and the characteristic holes during Swiss cheese manufacture.
• C. acnes antimicrobial resistance:
  • Information mainly gleaned from isolates in refractory cases of acne vulgaris, so correlation with the much less common systemic or deep infections are unclear.
  • 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 effect when either tetracycline or doxycycline-resistant strains of P. acnes are suspected.