Evaluation of virulence factor profiling in the characterization of veterinary Escherichia coli isolates

Abstract

Escherichia coli has been used as an indicator organism for fecal contamination of water and other environments and is often a commensal organism in healthy animals, yet a number of strains can cause disease in young or immunocompromised animals. In this study, 281 E. coli isolates from bovine, porcine, chicken, canine, equine, feline, and other veterinary sources were analyzed by BOXA1R PCR and by virulence factor profiling of 35 factors to determine whether they had utility in identifying the animal source of the isolates. The results of BOXA1R PCR analysis demonstrated a high degree of diversity; less than half of the isolates fell into one of 27 clusters with at least three isolates (based on 90% similarity). Nearly 60% of these clusters contained isolates from more than one animal source. Conversely, the results of virulence factor profiling demonstrated clustering by animal source. Three clusters, named Bovine, Chicken, and Porcine, based on discriminant components analysis, were represented by 90% or more of the respective isolates. A fourth group, termed Companion, was the most diverse, containing at least 84% of isolates from canine, feline, equine, and other animal sources. Based on these results, it appears that virulence factor profiling may have utility, helping identify the likely animal host species sources of certain E. coli isolates.

FIG. 1.

Results of BOXA1R primer and virulence factor PCR analysis for 281 E. coli isolates used in this study. The dendrogram to the left is based on the BOXA1R results. Red bars in the gel images indicate the bands present in each of the gels. For virulence factor PCR results, a blue box indicates detection of the virulence gene, and a golden box indicates the absence of a detectable gene. The columns to the right of the virulence genes indicate the animal source, state where the organism was isolated, and the year isolated, respectively. For the animal source, green isolates are porcine, red are bovine, yellow are chicken, light blue are canine, pink are feline, brown are equine, and purple are from other animal sources. For the states, green represents isolates from Arkansas, red are from Georgia, dark blue are from Missouri, yellow are from North Dakota, and turquoise are from Oklahoma. For the year of isolation, those marked in green are from 1992, red are from 1996, pink are from 1997, yellow are from 1998, turquoise are from 1999, and purple are from 2004.

FIG. 2.

Cumulative virulence factor PCR data were also analyzed by discriminant component analysis with variance in BioNumerics to determine grouping of isolates based on their cumulative virulence gene profiles. The isolates are represented by a symbol corresponding to the animal source group as follows: Bovine (★), Chicken (⊙), Swine (•), Canine (), Feline (), Equine (〉), and Other (). Four major clusters were identified, delineated by ovals on the figure, and defined by the predominant source (Bovine, Chicken, Swine, and Companion). Adjacent to the ovals are the number of isolates from different animal species present in the respective clusters.