THE HHA PROTEIN AS A MODULATOR OF EXPRESSION OF VIRULENCE FACTORS IN ESCHERICHIA-COLI

We constructed hha derivatives from both a clinical uropathogenic Esch erichia call isolate (strain FVL4) and a wild E. coil strain causing b ovine diarrhea (strain CCB21) and analyzed the effect of tile hha alle le on the expression of the different virulence factors exhibited by t hese strains. Expression of hemolysin and of the Vir antigen was alter ed in hha mutants. Whereas production of hemolysin by strain FVL4 was repressed both at a low temperature and at high osmolarity, the hha al lele accounted for a significant increase of hemolysin production unde r these conditions. Also, the low temperature-sensitive expression of the Vir adhesin was modified in hha mutants, which were able to expres s this adhesin at a low temperature. Expression of other virulence fac tors, such as cytotoxic necrotizing factor type 1 and 2 toxins, remain ed unmodified in hha derivatives of strains FVL4 and CCB21.