CATABOLITE REPRESSION OF THE ADHESION OF VERO CYTOTOXIN-PRODUCING ESCHERICHIA-COLI OF SEROGROUP-O157 AND SEROGROUP-O111

The virulence traits that mediate Vero cytotoxin-producing E. coli (VT EC) adherence are unclear. Many VTEC strains possess the eaeA gene whi ch is involved in the attaching and effacing effects of enteropathogen ic E. coli (EPEC). Most eae-positive VTEC adhered to HEp-2 cells in a localized manner; however some strains did not adhere. Thus we investi gated the adhesion of poorly adherent strains, especially those of ser ogroups 0111 and 0157. To establish a model, the adherence to HEp-2, I NT407 and Caco-2 cells of 12 0157 VTEC and six 0111 VTEC isolated from cases of human infection were studied after growth of the bacteria un der different conditions. For adhesion tests mannose is usually added during prior broth culture of the bacteria, and during the period of a ttachment, so that any adhesion due to mannose-sensitive type 1 pili i s inhibited. Bacteria cultured in peptone water in the absence of mann ose adhered to all three lines; there were localized clusters of bacte ria on 1%-82% cells, whether mannose was present during the attachment period or not. Bacteria grown in the presence of D-mannose, or any ot her sugar that was metabolized, showed little adherence (range 0-9%). alpha-Methyl-glucoside also caused marked inhibition of adhesion. It w as concluded that inhibition of adhesion was due to catabolite repress ion.