Peptostreptococcus spp. (and Finegoldia magna)


  • Anaerobic Gram-positive cocci: part of the normal flora of the mouth, GI and GU tracts as well as skin.
  • A heterogeneous group of "anaerobic streptococci" now classified into 5 groups and changes in the taxonomy that can be confusing.
    • For example, Finegoldia magna is the former Peptosteptococcus magnus.
  • Small cocci, may be seen on Gram stain in short chains and pairs.
    • GPC seen may appear identical to aerobic streptococci (chains) or staphylococci (clusters) [Fig].
    • Non-spore forming
  • Peptostreptococcus (which includes the former Peptococcus) account 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, often important in mixed infections. They are not Peptostreptococci and are not sensitive to metronidazole.

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Last updated: September 5, 2020