Peptostreptococcus spp. (and Finegoldia magna)

MICROBIOLOGY

• Anaerobic Gram-positive cocci: part of the normal flora of the mouth, GI and GU tracts, and skin.
• A heterogeneous group of "anaerobic streptococci" is now classified into five groups, and changes in the taxonomy can be confusing.
  
  • Peptoniphilus lacrimalis, P. ivorii, Anaerococcus octavius, Peptostreptococcus anaerobius and Micromonas micros.
  • Others were reclassified. For example, Finegoldia magna is the former Peptosteptococcus magnus.
• Small cocci may be seen on Gram stain in short chains and pairs.
  
  • GPC may appear identical to aerobic streptococci (chains) or staphylococci (clusters) [Fig].
  • Non-spore forming
• Peptostreptococcus (which includes the former Peptococcus) accounts for nearly all anaerobic GPC except Finegoldia magna.
• Most common and important: Finegoldia magna, P. asaccharolyticus.
  • Less common: P. micros, P. anaerobius.
• Note: Microaerophilic streptococci, such as Streptococcus intermedius Group, are pathogenic and often important in mixed infections.
  • They are not Peptidostreptococci and are not sensitive to metronidazole.