TABLE 3.

Categories of bacterial pyogenic infections of the musculature

Infection type	Causative agent(s)
Pyomyositis	Usually Staphylococcus aureusa
Psoas abscess	S. aureus, mixed gram-positive organisms, gram-negative aerobic and anaerobic organisms, Mycobacterium spp.a
Staphylococcus aureus myositis	S. aureus
Group A streptococcal necrotizing myositis	Streptococcus pyogenes
Group B streptococcal myositis	Streptococcus agalactiae
Clostridium species myositis, gas gangrene	Usually C. perfringens, but in spontaneous cases C. septicum
Nonclostridial myositis
Anaerobic streptococcal myonecrosis	Peptostreptococcus; also may involve group A streptococci and S. aureus
Synergistic nonclostridial myonecrosis	Streptococci and mix of other organisms
Aeromonas myonecrosis	Aeromonas hydrophila
Vascular gangrene	Proteus, Bacillus, Bacteroides, and others

^aSee Table 1 for other etiologic agents.