The importance of black-pigmented gram-negative anaerobes in human infections

Black-pigmented Gram-negative anaerobic rods are found on mucosal surfaces as indigenous flora. With mucosal damage due to disease, trauma or surgery, these organisms may invade tissues and set up infection. Other important factors determining whether or not infection results include 'inoculum' size, synergy with other organisms and production of virulence factors that include capsules, lipopolysaccharide, attachment factors, proteases, collagenase, neuraminidase, and phospholipase A; also, they may have fibrinolytic and anti-phagocytic activity and may degrade complement and IgG and IgM. Pigmented anaerobes are found in all types of infections including such serious infections as bacteraemia, endocarditis, intracranial abscess, necrotizing pneumonia and necrotizing fasciitis, generally as part of a mixed infecting flora, and they play a key role in experimental mixed infections. They dominate or are prominent in infections involving organisms originating in the oropharynx, such as central nervous system, head and neck, dental and pleuropulmonary infections. Therapy of infections involving pigmented anaerobes includes surgery plus antimicrobial agents; a significant percentage of strains produce beta-lactamase. Much remains to be done to determine the relative importance of the various taxa of black-pigmented Gram-negative anaerobes and of the different virulence factors produced by them.