VIRULENCE AND EPITHELIAL CELL INVASIVENESS OF DYSENTERY BACILLI

Studies on the pathogenicity of Shigella have been conducted, employing various experimental models and acid agglutination test with S. flexneri 2a strain 5503 and its variants. The parent strain 5503 isolated from a dysentery monkey behaved as a virulent one with respect to oral infectivity for monkeys, keratoconjunctival infectivity for guinea pigs, and penetration and multiplication within cultured monolayer cells, whereas variants 5503-I and 5503-II derived from strain 5503 were avirulent. Neither parenteral virulence for mice nor acid agglutinability gave consistent relation. The results obtained agreed well with those established by LaBrec et al.(1964). Localization of the dysentery bacilli and inflammatory reactions induced were followed by examining keratoconjunctivitis in guinea pigs by the fluorescent antibody and histopathological techniques. The significance in the pathogenesis of bacillary dysentery of epithelial cell penetration and intracellular multiplication of the bacilli is discussed in connection with oral infectivity for monkeys. Cultured monolayer cells of various human cell lines tested were equally susceptible to invasion of virulent strain 5503. Time-lapse cinemicrographic observations on the infection of Henle's intestine cells revealed the events which took place in the epithelial cell infection process.