An experimental mouse model to study the pathogenicity of Prevotella biviaand investigations of possible virulence

Induction of subcutaneous abscesses in mice was used to study the pathogeni city of Prevotella bivia both in mono-infection and in mixed cultures wit E scherichia coli and Peptostreptococcus spp. Virulence factors such as coagg regation and aggregate formation of cells, haemagglutination activity and t olerance to serum bactericidal activity were investigated for their possibl e role in P bivia pathogenicity. Monocultures of P bivia, E coli and Peptos treptococcus spp did not induce subcutaneous abscess at concentrations as h igh as 10(9) colony forming units/millilitre (cfu/ml). Only E coli persiste d at the infection site for up to 7 days post infection but with a marked d ecline in cell count (8.0 x 10(2) cfu/ml). The anaerobic organisms did not persist at the infection sites beyond the fifth day. In contrast, mixed cul tures of P bivia and E coli or all three organisms potentiated for infectiv e abscess two weeks after infection. Viable cells were recovered from absce sses in greater numbers as the infection progressed. Prevotella bivia was t he predominant organism in chronic abscesses while E coli predominated in a bscesses in the acute stage of the infection. Prevotella bivia lacked haema gglutination activity against human and sheep erythrocytes and showed marke d susceptibility to 50 per cent human serum. These may limit its haematogen ous spread. Its ability to form aggregates in molar salt solutions and coag gregate with facultative organisms may account for its persistence in patho logical sites.