EFFECT OF GROWTH CONDITION ON IN-VITRO SUSCEPTIBILITY OF SHIGELLA-DYSENTERIAE TYPE-1 TO KILLING BY MURINE PERITONEAL-MACROPHAGES

The intracellular fate of Shigella dysenteriae type 1 strains grown in casamino acid-yeast extract (CYE) broth and nutrient broth (NB) was s tudied in casein-elicited mouse peritoneal macrophages. Virulent strai ns 14731 and W30864 cultured in NB and opsonised with normal mouse ser um were susceptible to killing by peritoneal macrophages (66 SEM 1.7% killing by 2 h). In contrast, both strains grown in CYE broth and opso nised with normal mouse serum showed resistance to killing by peritone al macrophages (76 SEM 1.4% survival by 2 h). Electronmicroscopy demon strated that the bacteria escaped from the phagosome compartment by ly sing the phagocytic vacuole and remained within the cytoplasm. Lipopol ysaccharide (LPS) stimulated peritoneal macrophages to kill the opsoni sed strains 14731 and W30864 grown in CYE broth (85.4 SEM 1.6% killing by 2 h). Recombinant murine gamma interferon (rIFN-gamma) also stimul ated macrophages to kill CYE-grown bacteria (52.1 SEM 1.3% killing by 2 h). However, an avirulent rough mutant strain W30864-22 grown in eit her NE or CYE broth showed marked susceptibility to killing by periton eal macrophages, which was similar to that of NB-grown strain 14731 or W30864. The results of the present study suggest that in-vitro growth conditions may modulate the susceptibility of S. dysenteriae type 1 t o killing by phagocytes.