ENTEROPATHOGENIC ESCHERICHIA-COLI PROTEIN SECRETION IS INDUCED IN RESPONSE TO CONDITIONS SIMILAR TO THOSE IN THE GASTROINTESTINAL-TRACT

The pathogenicity of enteropathogenic Escherichia coli (EPEC) is assoc iated with the expression and secretion of specific bacterial factors. EspB is one such secreted protein which is required to trigger host s ignaling pathways resulting in effacement of microvilli and cytoskelet al rearrangements. These events presumably contribute to the ensuing d iarrhea associated with EPEC infections, EPEC encounters several envir onmental changes and stimuli during its passage from the external envi ronment into the host gastrointestinal tract. In this paper me show th at the secretion of EspB is subject to environmental regulation, and m aximal secretion occurs under conditions reminiscent of those in the g astrointestinal tract. Thus, secretion is maximal at 37 degrees C, pH 7, and physiological osmolarity. In addition, maximal secretion requir es the presence of sodium bicarbonate and calcium and is stimulated by millimolar concentrations of Fc(NO3)(3). The secretion of the four ot her EPEC-secreted proteins appears to he modulated in a manner similar to that of EspB. Our results also show that secretion is not dependen t on CO2, as originally reported by Haigh et al, (FEMS Microbiol. Lett . 129: 63-67, 1995), but that CO2 more likely acts as a component of t he medium buffering system, since CO, dependence was abolished by the use of alternative buffers.