Distribution of the serine protease autotransporters of the Enterobacteriaceae among extraintestinal clinical isolates of Escherichia coli

Abstract

Urinary tract infections continue to be among the most common extraintestinal diseases. Cystitis in women is by far the most common urinary tract infection; pyelonephritis in both sexes and prostatitis in men are more severe but less frequent complaints. Escherichia coli is by far the most common cause of urinary tract infection. It is believed that uropathogenic E. coli is adept at colonizing the urinary tract via the production of specific virulence factors. Recently, a novel virulence determinant, Vat, was described for the prototypical uropathogenic E. coli strain CFT073. Vat is a member of the SPATE (serine protease autotransporters of the Enterobacteriaceae) subfamily of the autotransporters. Previously, SPATEs have been described for all pathovars of E. coli, but until recently their presence had been noticeably absent in nonpathogenic E. coli. In this report we describe the prevalence and phylogenetic distribution of the SPATEs among uropathogenic E. coli and the ECOR collection, demonstrating an association between the presence of the SPATEs, including Vat, and uropathogenic E. coli phylogroups. In addition, we describe the distribution of SPATEs among nonpathogenic E. coli.

FIG. 1.

Genetic organization of the proA-yagU region of E. coli. The gene organization and content of the proA-yagU region of genome-sequenced E. coli strains is depicted. The vat gene is found in the same position and orientation in all the extraintestinal pathogens but is absent from the intestinal pathogenic isolates. With the exception of several genes conserved among EAEC 042, EHEC EDL933, and E. coli K12, the genetic content of each island is remarkably distinct, indicating that this region is a hotspot for recombination. Loci shared between pathogenicity islands are highlighted in the same color. Loci previously implicated in pathogenesis are shaded and labeled. UPEC, uropathogenic E. coli; NMEC, neonatal meningitis E. coli; EPEC, enteropathogenic E. coli; EHEC, enterohaemorrhagic E. coli; EAEC, enteroaggregative E. coli.

FIG. 2.

Distribution of SPATEs among the ECOR collection. Phylogenetic tree of the ECOR isolates showing the distribution of vat and SPATE-encoding genes where each locus is represented by a shaded box as indicated in the figure. The number of the ECOR isolate is given in boldface, and each of the major phylogenetic branches is indicated. The vat gene is preferentially associated with the B2 phylogenetic cluster, whereas SPATE-encoding genes show a wider distribution. The figure was adapted from reference .

FIG. 3.

Prevalence of SPATEs in extraintestinal E. coli clinical isolates. The vat and SPATE-encoding loci were detected by PCR in clinical isolates of E. coli. Prevalence is indicated as a percentage of the total population of strains associated with each clinical syndrome. No statistically significant difference in the distribution of SPATEs was observed among the extraintestinal clinical isolates. The vat gene is present at a significantly higher rate in prostatitis isolates when compared to septicemia strains; however, the prevalence of vat among the other groups is statistically similar.

FIG. 4.

ClustalX phylograms of amino acid sequence alignments of full-length SPATE passenger domains (A) or the β-domains (B). (A) The known substrates for each of the SPATEs is indicated. In addition, the oligopeptide sequences known to be recognized and cleaved by the SPATEs are also depicted. The bifurcating pattern of SPATE distribution can be observed, where with the exception of Vat the cytopathic SPATEs are found in group A and those identified as extracellular proteases are located in Group B. (B) The β-domains do not have the same phylogenetic pattern and have undergone more restricted recombination events. Trees were further tested for reliability using bootstrap analysis, yielding results of 96.9% (A) and 99.4% (B).