PATHOGENICITY OF PEPTOSTREPTOCOCCUS-MICROS MORPHOTYPES AND PREVOTELLASPECIES IN PURE AND MIXED CULTURE

Recently, an atypical rough colony morphotype of Peptostreptococcus mi cros, a species which is found in ulcerating infections, including per iodontitis, was isolated. The virulence of morphotypes alone and in co mbination with Prevotella intermedia and P. nigrescens was investigate d both in vivo and in vitro. All strains tested induced abscesses cont aining fluid pus in a mouse skin model, and lesions caused by monocult ures of the rough morphotype strains of P. micros were statistically s ignificantly larger than those induced by the smooth morphotype strain s. Inocula containing both morphotypes produced similar sized abscesse s compared to mono-inocula containing the same bacterial load. Both Pr evotella species induced small abscesses when inoculated alone, and wh en Pr. nigrescens was inoculated with one of the other strains, the ab scesses were not significantly different from the abscesses induced by the mono-infections of this strain. Synergy, in terms of higher numbe rs of colony forming units (cfu) in the mixed inocula, was found for a ll combinations of the rough morphotypes of P. micros and both Prevote lla spp. Pus from abscesses caused by combinations of Peptostreptococc us and Prevotella spp. transmitted the infection to other mice, but no abscesses were formed in mice inoculated with pus induced by mono-ino cula. These results demonstrated synergic activity between both rough and smooth P. micros strains and oral Prevotella strains. The in-vitro co-culture experiments produced no evidence of growth stimulation. Th e effect of P. micros strains on the immune system was investigated by testing their ability to initiate luminol-dependent chemiluminescence of polymorphonuclear leucocytes in the presence and absence of human serum. In the latter, the rough morphotype strains initiated higher co unts than the smooth morphotype strains. Further work is needed to elu cidate the difference in virulence between the smooth and the rough mo rphotype cells of P. micros and the nature of the interaction with the Prevotella spp.