New fimbrial gene cluster of S-fimbrial adhesin family

Fimbrial adhesins that mediate attachment to host cells are produced by mos t virulent Escherichia coil isolates, These virulence factors play an impor tant role in the initial stages of bacterial colonization and also in deter mination of the host and tissue specificity. Isolates belonging to serotype O78 are known to cause a large variety of clinical syndromes in farm anima ls and humans and have been shown to produce several types of adherence fim briae. We studied the fimbrial adhesin from an avian septicemic E. coli iso late of serotype O78, Analysis of the genetic organization of the fac (fimb ria of avian E. coli) gene cluster indicates that it belongs to the S-fimbr ial adhesin family. Seven open reading frames coding for major and minor st ructural subunits were identified, and most of them showed a high degree of homology to the corresponding Sfa and Foc determinants. The least-conserve d open reading frame was facS, encoding a protein known to play an importan t role in determining adherence specificity in other S-fimbrial gene cluste rs.