Antigen-43-mediated autoaggregation of Escherichia coli is blocked by fimbriation

Antigen 43 (Ag43), the product of the flu gene, is a surface-displayed auto transporter protein of Escherichia coli, Ag43 is responsible for the autoag gregation and flocculation of static liquid cultures of many E, coli strain s. The expression of Ag43 has been reported to be phase variable and contro lled by the product of the oxyR gene, Type 1 fimbriae are thin adhesive thr ead-like surface organelles responsible for bacterial receptor recognition and tissue colonization. Like that of Ag43, the expression of type 1 fimbri ae is phase variable. Interestingly, previous results have suggested that t he expression of type 1 fimbriae and the expression of Ag43 are mutually ex clusive. In the present report, we show, by use of well-defined mutants, th at fimbriation abolishes Ag43-mediated autoaggregation but does not affect Ag43 expression. Autoaggregation is shown to require an intercellular Ag43 Ag43 interaction, and the physical presence of fimbriae on the cells seems to abrogate this interaction. The Ag43 or OxyR status does not appear to in fluence fimbria expression, and our results suggest that the expression of Ag43 and the expression of fimbriae are independent processes.