Genes Related to Long Polar Fimbriae of Pathogenic Escherichia coliStrains as Reliable Markers To Identify Virulent Isolates

ABSTRACTLpf (stands for long polar fimbriae) is one of the few adhesive factors of enterohemorrhagic Escherichia coliO157:H7 associated with colonization of the intestine. E. coliO157:H7 strains possess two lpfloci encoding highly regulated fimbrial structures. Database analysis of the genes encoding the major fimbrial subunits demonstrated that they are present in commensal as well as pathogenic (both intestinal and extraintestinal) E. colistrains and in Salmonellastrains and that the lpfA1and lpfA2genes are highly prevalent among LEE (locus of enterocyte effacement)-positive E. colistrains associated with severe and/or epidemic disease. Further DNA sequence analysis of the lpfA1and lpfA2genes from different attaching-and-effacing E. colistrains has led us to the identification of several polymorphisms and the classification of the major fimbrial subunits into distinct variants. Using collections of pathogenic E. coliisolates from Europe and Latin America, we demonstrated that the different lpfAtypes are associated with the presence of specific intimin (eae) adhesin variants and, most importantly, that they are found in specific E. colipathotypes. Our results showed that the use of these fimbrial genes as markers, in combination with the different intimin types, resulted in a specific test for the identification of E. coliO157:H7, distinguishing it from other pathogenic E. colistrains.