DIFFERENTIAL REGULATION OF FASA AND FASH EXPRESSION OF ESCHERICHIA-COLI 987P FIMBRIAE BY ENVIRONMENTAL CUES

An early process in the pathogenesis of enteric bacteria is colonizati on of the intestinal epithelium leading to local multiplication, patho physiological interactions with the host and further spreading. Attach ment is typically mediated by bacterial fimbriae, which are selectivel y expressed during growth in the intestine. Here we report an analysis of the regulation of 987P fimbrial expression of enterotoxigenic Esch erichia coli (ETEC). Expression of both fasH, the transcriptional acti vator of the 987P fimbrial genes, and fasA, the major fimbrial subunit , is regulated in response to a variety of environmental stimuli. We h ave found that expression of fasH is regulated in response to the carb on status of the growth medium by the cAMP-CRP complex. Moreover, fasH is regulated in response to both the nitrogen status of the growth me dium and the external pH. Expression of fasA is activated by FasH, and is also selectively regulated in response to growth temperature by HN S. Regulation of fimbrial expression by carbon and/or nitrogen gradien ts is proposed to provide a mechanism that allows preferential coloniz ation of different segments of the intestine by various enteropathogen s, such as ETEC, enteropathogenic E. coli and Vibrio cholerae.