Pathogenicity of Peptostreptococcus micros morphotypes and Prevotella species in pure and mixed culture

Recently, an atypical rough colony morphotype of Peptostreptococcus micros, a species which is found in ulcerating infections, including periodontitis, was isolated. The virulence of morphotypes alone and in combination with Prevotella intermedia and P. nigrescens was investigated both in vivo and in vitro. All strains tested induced abscesses containing fluid pus in a mouse skin model, and lesions caused by monocultures of the rough morphotype strains of P. micros were statistically significantly larger than those induced by the smooth morphotype strains. Inocula containing both morphotypes produced similar sized abscesses compared to mono-inocula containing the same bacterial load. Both Prevotella species induced small abscesses when inoculated alone, and when Pr. nigrescens was inoculated with one of the other strains, the abscesses were not significantly different from the abscesses induced by the mono-infections of this strain. Synergy, in terms of higher numbers of colony forming units (cfu) in the mixed inocula, was found for all combinations of the rough morphotypes of P. micros and both Prevotella spp. Pus from abscesses caused by combinations of Peptostreptococcus and Prevotella spp. transmitted the infection to other mice, but no abscesses were formed in mice inoculated with pus induced by mono-inocula. 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. The 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 counts than the smooth morphotype strains. Further work is needed to elucidate the difference in virulence between the smooth and the rough morphotype cells of P. micros and the nature of the interaction with the Prevotella spp.

Schistosomicidal activities of Lymnaea stagnalis haemocytes: the role of oxygen radicals

Macrophage-like defence cells (haemocytes) of the pond snail Lymnaea stagnalis mediate cytotoxicity through reactive oxygen intermediates (ROIs). This activity is NADPH-oxidase dependent, as in mammalian phagocytes during the respiratory burst. In this study, mother sporocysts of schistosomes, the compatible Trichobilharzia ocellata and the incompatible Schistosoma mansoni evoke in vitro ROI activities (detected by luminol dependent chemiluminescence, LDCL) from L. stagnalis haemocytes. S. mansoni is encapsulated by haemocytes and eliminated, whereas T. ocellata escapes encapsulation and survives. Both schistosomes were equally susceptible to in vitro oxidative damage from exposure to hydrogen peroxide and to ROIs generated by a xanthine/xanthine oxidase system. Protocatechuic acid, a specific antagonist of NADPH-oxidase, delayed the killing of T. ocellata and S. mansoni sporocysts by haemocytes of resistant snails (Biomphalaria glabrata and L. stagnalis, respectively). We conclude that ROIs take part in haemocyte-mediated cytotoxicity. However, neither a snail's capability to generate ROIs, nor a schistosome's susceptibility to ROIs, determine snail/schistosome incompatibility. Snail/schistosome compatibility is rather determined by the parasite's ability to modulate haemocyte behaviour such that effective encapsulation and the generation of lethal concentrations of ROIs are prevented.

NADPH-oxidase activity: the probable source of reactive oxygen intermediate generation in hemocytes of the gastropod Lymnaea stagnalis

Macrophage-like defense cells (hemocytes) of the pond snail Lymnaea stagnalis generate reactive oxygen intermediates (ROIs) upon contact with non-self, following kinetics similar to those of ROI production by mammalian leukocytes during respiratory burst. In this study, several inhibitors of NADPH-oxidase, the key enzyme of the respiratory burst in mammalian phagocytes, were tested for their effect on oxidative activities [as demonstrated by nitroblue tetrazolium (NBT) reduction and luminol-dependent chemiluminescence (LDCL)] of phagocytosing snail hemocytes. In the presence of diphenylene iodonium, zymosan-stimulated hemocytes of L. stagnalis failed to reduce NBT and showed a markedly reduced LDCL response. Also, compounds that prevent assembly of functional NADPH-oxidase complexes in activated mammalian cells were effective; preincubation of hemocytes with 1,4-naphthoquinone inhibited the LDCL response and NBT reduction upon phagocytic stimulation. Furthermore, coincubation but not preincubation with five different catechol-like phenols inhibited oxidative activities of zymosan-stimulated hemocytes. These results imply similarities in composition and regulation of the ROI-generating mechanisms of both mammalian and snail defense cells. It is postulated that in L. stagnalis hemocytes, (1) NADPH-oxidase activity is responsible for ROI production, (2) an active NADPH-oxidase enzyme complex has to be assembled from putative cytosolic and membrane-associated components, and (3) continuous replacement of active NADPH-oxidase enzyme complexes is necessary to sustain respiratory burst-like oxidative activities during interactions with non-self.

A comparative study of hemocytes from six different snails: morphology and functional aspects

Hemocytes taken from six different gastropod snails, Achatina achatina, A. fulica, Biomphalaria glabrata, Bulinus natalensis, Helix aspersa, and Lymnaea stagnalis, were compared for morphology, peroxidase activity, and, using methods developed for L. stagnalis, the ability to generate reactive oxygen inermediates upon phagocytic stimulation. Numbers of hemocytes per milliliter hemolymph and hemocytes' microscopical morphology showed some variation among the snail species. Peroxidase activity was demonstrated in all snail hemocytes except in those of B. glabrata and A. fulica. Hemocytes of all species generated superoxide upon phagocytic stimulation with zymosan (tested by superoxide dismutase-inhibitable reduction of nitroblue tetrazolium). When tested, hemocytes of A. achatina and of A. fulica displayed luminol-dependent chemiluminescence activity.