Pathotype and Genotype Determination of Isolates of Escherichia coli Obtained from the Production Chain of Jalapeño Pepper, Tomato and Melon in Northeast Mexico

Introduction: While most Escherichia coli strains are commensal in nature, some are pathogenic.  Six major pathotypes exist, as classified according to metabolic characteristics and virulence factors, including ETEC: enterotoxigenic and EPEC: enteropathogenic. Another way to classify E. coli strains, typically used for microbial source tracking, is to analyze phylogenetic cluster characteristics, where A, B1, B2 and D are the main genotypes. Furthermore, to increase the discrimination power of E. coli population analyses, the use of subgroups A₀, A₁, B1, B2₂, B2₃, D₁ and D₂, has been proposed.

Purpose: To identify pathotypes and genotypes from 345 isolates of E. coli obtained from the production chain of jalapeño pepper, tomato and melon in Northeast Mexico.

Methods: Genotypic subgroups (A₀, A₁, B1, B2₂, B2₃, D₁ and D₂), were determined by analysis (presence/absence) of a combination of the genetic markers using TSPE4.C2, chuA and yjaA primers by PCR. Pathotypes were determined by multiplex PCR according to Vidal et al., 2005 using stII, virF, ipaH, daaE, aafII, lt, stx₁, stx₂, eae y bfp primers. 

Results: Relative to genotype, most of the isolates belonged to phylogenetic group A (297 isolates or 86 %). Twenty-five isolates (7.2%) belonged to genotype B1; 20 (5.8%) to genotype D; and only 3 (0.9%) to genotype B2. These isolates were grouped into seven phylogenetic subgroups: 58% A₀, 27% A₁, 7% B1, 0.3% B2₂, 0.6% B2₃, and 5.8% D_1. No isolates were genotyped as D₂. The high prevalence of genotype A and B1 suggests that most of those isolates were commensals from gut microflora and therefore non-pathogenic.   Only four isolates (1.2%) were positive for pathotype grouping, three for EPEC and one for ETEC. 

Significance: Although at low levels, potentially pathogenic E. coli strains were present in the production environment of these crops and could represent a health risk.