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.

Adhesin-Encoding Genes from Shiga Toxin-Producing Escherichia coli Are More Prevalent in Atypical than in Typical Enteropathogenic E. coli

“…The distribution of lpfA in tEPEC agreed with our previous study (26); however, this is the first description of isolates lpfA1-1 allele positive and lpfA2 negative in serotype O142:H34 (Table 4). From the 100 aEPEC strains analyzed, 41 lack both lpfA alleles.…”

“…Of the remaining 59 lpfA-positive strains, 20 contained the combination of lpfA1-2 and lpfA2-1 alleles. With the exception of one strain, all O55:H7 strains were lpfA1-3 and lpfA2-2, thus confirming previous findings with EHEC O157:H7 and LEE-negative STEC strains (10,26), that demonstrated that the presence of these two alleles is a reliable way to detect O157:H7 strains and the closely related O55:HϪ or O55:H7 serotypes. Although different combinations of these alleles were detected in aEPEC serotypes, we found that seven O119:H2 isolates carried the lpfA1-2 allele and were negative for lpfA2 (Table 3).…”

“…Various additional adhesins have been described in STEC, including Saa (STEC autoagglutinating adhesin) in LEE-negative STEC strains (18); Paa (porcine A/E-associated adhesin), involved in the initial adherence of porcine EPEC strains (4); Lpf (long polar fimbriae), an adhesin found in EHEC and other pathogenic E. coli (26,27); ToxB (EHEC pO157 plasmid-encoded protein), which is involved in adherence of EHEC O157:H7 (24); Iha (IrgA homologue adhesin), an adhesin similar to Vibrio cholerae IrgA (23); and EspP (extracellular serine protease), which contributes to bovine intestinal colonization (9). aEPEC strains are a highly heterogeneous group, with many strains presenting an assorted repertoire of virulence genes from various E. coli pathotypes (8,11,20,25,30).…”

“…The presence of different lpfA alleles was investigated by PCR using primers and conditions previously described (26). Data were analyzed by two-tailed Fisher's exact test, and P values of Յ0.05 were considered statistically significant.…”

Long Polar Fimbriae of Enterohemorrhagic Escherichia coli O157:H7 Bind to Extracellular Matrix Proteins

“…This process involves the recognition of receptor(s), located at the surface of the target cells, by adhesion factors expressed on the bacterial surface (23,35). To date, the intimin protein and the long polar fimbriae (Lpf) are the only two factors of EHEC that have been demonstrated to play a role in persistence and the colonization of the intestine (5,9,12,17,29,33). Further, the presence of intimin-negative EHEC strains that can cause severe disease in humans, including HUS (22), have led to the discovery of other putative adhesins (10, 15, 16, 20, 21, 24-26, 30, 31, 37, 39).…”