Detection and Characterization of the Fimbrial sfp Cluster in Enterohemorrhagic Escherichia coli O165:H25/NM Isolates from Humans and Cattle

Abstract

The sfp cluster, encoding Sfp fimbriae and located in the large plasmid of sorbitol-fermenting (SF) enterohemorrhagic Escherichia coli (EHEC) O157 (pSFO157), has been considered a unique characteristic of this organism. We discovered and then characterized the sfp cluster in EHEC O165:H25/NM (nonmotile) isolates of human and bovine origin. All seven strains investigated harbored a complete sfp cluster (carrying sfpA, sfpH, sfpC, sfpD, sfpJ, sfpF, and sfpG) of 6,838 bp with >99% nucleotide sequence homology to the sfp cluster of SF EHEC O157:NM. The sfp cluster in EHEC O165:H25/NM strains was located in an ϳ80-kb (six strains) or ϳ120-kb (one strain) plasmid which differed in structure, virulence genes, and sfp flanks from pSFO157. All O165:H25/NM strains belonged to the same multilocus sequence type (ST119) and were only distantly phylogenetically related to SF EHEC O157:NM (ST11). The highly conserved sfp cluster in different clonal backgrounds suggests that this segment was acquired independently by EHEC O165:H25 and SF EHEC O157:NM. Its presence in an additional EHEC serotype extends the diagnostic utility of PCR targeting sfpA as an easy and efficient approach to seek EHEC in patients' stools. The reasons for the convergence of pathogenic EHEC strains on a suite of virulence loci remain unknown.

Comparative genomics reveal the mechanism of the parallel evolution of O157 and non-O157 enterohemorrhagic Escherichia coli

“…3B). This result is not attributable to the genome size effect, because the numbers of CDS families identified in each EHEC (4,965) are in a range observed for other E. coli strains (5,101-4,033), whereas all Shigella strains contain much lower numbers of CDS families (see Table S1). Furthermore, to avoid biases introduced by different gene prediction criteria, we performed 1-way comparisons by using the TBLASTN homology search (see Fig.…”

“…Interestingly, strains with the same pathotype have occasionally emerged from multiple lineages, but the genetic mechanisms underlying such parallel evolution are not fully understood. Enterohemorrhagic Escherichia coli (EHEC) strains present a striking example of this phenomenon (3,4).…”

Recent Advances in Understanding Enteric Pathogenic Escherichia coli

“…Expression of the sfp under laboratory conditions required anaerobic conditions (312). Although sfp is gen- erally thought to be restricted to SFO157:NM isolates, it has been found in STEC O165:H25/NM (313). Other proteins that are thought to be involved in LEE-positive STEC adherence are Efa-1/LifA and its homolog, ToxB (314,315).…”

The Accessory Genome of Shiga Toxin-Producing Escherichia coli Defines a Persistent Colonization Type in Cattle

“…Some of these serotypes have been linked to severe human HUS cases (e.g., O165:H25 or O26:H11), but other serotypes have not appeared in this context until now (e.g., O156:H25). The isolation of the latter from diarrheic or asymptomatic humans has only been reported sporadically (22)(23)(24). Geue et al (18) did identify O157:H7/HϪ STEC among the isolates from the herds, but in lower numbers than the serotypes mentioned above, e.g., only once in one animal in one of the tested herds in contrast to O165:H25 STEC, which was isolated repeatedly in the same herd from 8 different cattle over a 12-month period (20).…”