Adhesion and invasion of a mutant Shigella flexneri to an eukaryotic cell line in absence of the 220-kb virulence plasmid

A Shigella flexneri strain, cured of the large 220-kb virulence plasmid, ex presses adhering and invading ability in confluent monolayers of HeLa cells similar to its parent strain. Invasion by both the parent and the cured st rains resulted in alteration of the monomeric actin (G) in the total actin pool of HeLa cells. Other indicators of invasive characteristics of virulen t Shigella strains such as production of keratoconjunctivitis in guinea pig eye in vivo, Congo red binding and expression of contact hemolysin however , indicated loss of invasive properties in the plasmid cured strain. Furthe r, pretreatment of bacterial cells with para-bromophenacyl bromide (p-BPB), a specific chemical inhibitor of phospholipase A, adversely affected adhes ion to and invasion of HeLa cells in vitro, irrespective of the presence of the 220-kb plasmid indicating the possible involvement of the enzyme phosp holipase A in the invasion process. Adherence of both the strains to guinea pig colonic epithelial cells (CECs) in vitro was reduced significantly on pretreatment of bacteria or CECs with p-BPB. Expression of exocellular enzy mes viz. protease, elastase, phospholipase A and phospholipase C were not r elated to the large plasmid. (C) 1999 Published by Elsevier Science B.V. Ai l rights reserved.