SUMMARY: Tyzzer's disease organism was grown in primary monolayer cultures of adult mouse hepatocytes prepared by collagenase perfusion. The organisms produced a plaque-like cytopathic effect involving almost the whole culture around 72 h post-infection when the bacterial growth reached a maximum. The organisms showed specific immunofluorescence, and electron microscopy revealed that intracellular organisms had peritrichous flagella and underwent cell division. After intravenous inoculation of the infected cell culture into mice, necrotic hepatitis was produced and the organisms, recovered from the liver lesion, could be propagated in primary culture of mouse hepatocytes.
SUMMARY: A proteinase-deficient mutant of Candida albicans, M12, was produced by nitrosoguanidine mutagenesis of a proteinase-producing strain, ATCC 28366. The mutant was phenotypically identical to its parent in nearly all biochemical and morphological characteristics except proteinase production. The mutant was considerably less lethal than the parent when inoculated intravenously into mice and lower counts of C. albicans were recovered from the organs of mice infected with the mutant. Both strains were phagocytosed and killed to a similar extent by human and murine polymorphonuclear leukocytes when the yeasts were grown in a medium that did not induce proteinase production. However, in a proteinase-inducing medium, ATCC 28366 was phagocytosed and killed less well than M12. These results indicate that proteinase secretion by C. albicans is one factor determining the virulence of the species, but that other virulence factors are also involved in the pathogenesis of systemic candidosis.
SUMMARY: Many insects have a cell-free immune system in which small basic proteins called cecropins are the main defence against Gram-negative bacteria. We have earlier shown that an insect pathogenic strain of Serratia marcescens was resistant to insect immunity and that certain mutants resistant to phage φJ become sensitive to cecropins. We have found that protease-deficient mutants with and without resistance to φJ appear to be deficient in the mechanism of protease induction. Three different protease fractions exist and for two of the enzymes we describe a partial purification and characterization. The proteases show pronounced autodegradation which increases with the purity. Both enzymes are only partly affected by EDTA and they are highly toxic to Drosophila melanogaster. All three enzymes destroy cecropins in immune haemolymph from Cecropia pupae. However, in vivo experiments with different mutants indicate that in Serratia, passive resistance to insect immunity is more important for virulence in Drosophila than the production of proteases which can destroy cecropins.