DOWN-REGULATION OF INTIMIN EXPRESSION DURING ATTACHING AND EFFACING ENTEROPATHOGENIC ESCHERICHIA-COLI ADHESION

Enteropathogenic Escherichia coli (EPEC) produces attaching: and effac ing (;VE) lesions in the intestinal mucosa. The intimate bacterial adh esion associated with A/E lesion formation is promoted by intimin, 3 9 4-kDa EPEC surface protein,, Anti-intimin antisera raised in rabbits b y using the purified 280-amino-acid cell binding domain of intimin as the immunogen were employed in immunofluorescence and immunoelectron m icroscopical studies to investigate the expression of intimin by class ical EPEC strain E2348/69 (O127:116) and defined E2348/69 derivatives during culture growth and NE bacterium adhesion to cultured HEp-2 cell s, In stationary-phase broth cultures, only a small fraction of E2348/ 69 bacteria expressed intimin, and of those that did, immunolabelling revealed a uniform distribution of intimin over the bacterial surface; increased numbers of bacteria expressing intimin were detected when E 2348/69 was grown in tissue culture medium, an effect not seen with st rain JPN15, a virulence plasmid-cured derivative of E2348/69. Strain C VD206, an caeA mutant of E2348/69, did not stain with the anti-intimin antisera, but strain CVD206(pCVD438), containing a functional eaeA ge ne, stained uniformly, After a 3-h incubation of HEp-2 cells with stra in E2348/69, double immunofluorescence Labelling of intimin and cellul ar actin revealed strong intimin expression by all NE bacteria, but af ter 6 h of incubation, intimin expression by most E2348/69 bacteria wa s greatly reduced or not detected, This effect on intimin expression,v as not observed with strain JPN15 but was restored for strain JPN15(pC VD450) harboring the virulence plasmid-encoded per genes, These result s indicate that surface expression of intimin is regulated by environm ental factors during bacterial growth and following IVE lesion formati on and that virulence plasmid-encoded genes participate in these regul ation processes.