Genes related to long polar fimbriae of pathogenic Escherichia coli strains as reliable markers to identify virulent isolates

Abstract

Lpf (stands for long polar fimbriae) is one of the few adhesive factors of enterohemorrhagic Escherichia coli O157:H7 associated with colonization of the intestine. E. coli O157:H7 strains possess two lpf loci 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. coli strains and in Salmonella strains and that the lpfA1 and lpfA2 genes are highly prevalent among LEE (locus of enterocyte effacement)-positive E. coli strains associated with severe and/or epidemic disease. Further DNA sequence analysis of the lpfA1 and lpfA2 genes from different attaching-and-effacing E. coli strains 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. coli isolates from Europe and Latin America, we demonstrated that the different lpfA types are associated with the presence of specific intimin (eae) adhesin variants and, most importantly, that they are found in specific E. coli pathotypes. 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. coli O157:H7, distinguishing it from other pathogenic E. coli strains.

FIG. 1.

Trees based on sequence data from the lpfA1 (A) and lpfA2 (B) genes. Shown are the phylogenetic positions of the 525-bp and 603-bp E. coli O157:H7 lpfA1 and lpA2 genes from strain EDL933, respectively, and the corresponding lpfA1 and lpfA2 DNA sequences from E. coli and Salmonella strains currently available in GenBank (for accession numbers, see Materials and Methods). The occurrence (percentage) of the branching order in 1,000 bootstrapped trees is given at each branch. E. coli strains (with serotypes given in parentheses) listed include EDL933, EC4115, and Sakai (O157:H7), DEC5A (O55:H7), DEC7A (O157:H43), DEC8B (O111:H8), DEC10A (O26:H11), DEC11A (O128:H2), DEC15A (O111:H21), ECOR7 (O85:HNT), ECOR23 (O86:H43), ECOR28 (O104:NM), ECOR30 (O13:H21), ECOR33 (O7:H21), ECOR36 (O79:H25), ECOR40 (O7:NM), ECOR42 (ONT:H26), ECOR46 (O1:H6), ECOR48 (ONT:HNT), ECOR65 (ONT:H10), ECOR67 (O4:H43), O119-53 (O119:NM), E2348/69 (O127:H6), EH41 (O113:H21), O44-20 (O44), IAI1 (O8), 83/39 (O15:H−), O26:H11 (O26:H11), ED1a (O81), 789 (O78), chi7122 (O78:H9), SE11 (O152:H28), O15 (verocytotoxigenic E. coli O15), E24377A (ETEC O139:H28), and 55989 (EAEC). Salmonella enterica strains listed (with serovars given in parentheses) include P125109 (S. Enteritidis), CT02021853 (S. Dublin), SL254 (S. Newport), SL476 (S. Heidelberg), and LT2 (S. Typhimurium).