Correlation between pathogenicity of Shigella and intraperitoneal survival in mice.

Phagocytosis of virulent and avirulent strains of Shigella and Escherichia coli in the mouse peritoneum was studied. A direct correlation between bacterial virulence and resistance to phagocytosis by peritoneal phagocytes was demonstrated. Virulent strains were less readily cleared and were able to multiply to a limited extent within the peritoneal cavity. An epimerase-deficient, rough mutant of S. flexneri 2a was highly susceptible to phagocytosis. Restoration of the cell wall structure in these mutants resulted in a significant increase in their resistance to phagocytosis. Susceptibility to phagocytosis in smooth S. flexneri was age-dependent. Cells from 16-hr cultures were more resistant to removal from the peritoneum than were cells from 48- and 72-hr cultures.