Clonal relationship among atypical enteropathogenic Escherichia coli strains isolated from different animal species and humans

Abstract

Forty-nine typical and atypical enteropathogenic Escherichia coli (EPEC) strains belonging to different serotypes and isolated from humans, pets (cats and dogs), farm animals (bovines, sheep, and rabbits), and wild animals (monkeys) were investigated for virulence markers and clonal similarity by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). The virulence markers analyzed revealed that atypical EPEC strains isolated from animals have the potential to cause diarrhea in humans. A close clonal relationship between human and animal isolates was found by MLST and PFGE. These results indicate that these animals act as atypical EPEC reservoirs and may represent sources of infection for humans. Since humans also act as a reservoir of atypical EPEC strains, the cycle of mutual infection of atypical EPEC between animals and humans, mainly pets and their owners, cannot be ruled out since the transmission dynamics between the reservoirs are not yet clearly understood.

FIG. 1.

The phylogenetic (splits) network was based on the neighbor-net algorithm using a p distance matrix. The clusters of strains found on Bayesian analysis are indicated by gray boxes.

FIG. 2.

Inferred phylogeny of 49 typical and atypical EPEC strains isolated from humans and different animal species. The strains were rooted with E. coli strains EDL933 and E2348/69; S. enterica strain Ty2 was included as an outgroup standard. (A) Phylogenetic tree inferred by Bayesian analysis. The serotypes and sources of the strains are listed. The nucleotide substitution model best fit was constructed using GTR+I+G (where GTR is general time reversible, I is the proportion of invariable sites, and G is gamma) where G = 0.6931 and I = 0.5112. In the majority of cases, the tree is supported by Bayes credibility values higher than 90%. ST9 was the only ST representing two serotypes. (B) ML-inferred tree with similar topology and groups found on Bayesian analysis. The serotypes of each group found are listed. The ML tree was constructed with the model TrN+I+G, where TrN is Tamura-Nei, G = 0.6876, and I = 0.5139. In the majority, the tree is supported by bootstrapping values higher than 80%.

FIG. 3.

PFGE profiles and clusters of human and animal typical and atypical EPEC strains. The corresponding MLST sequence types, as well as the serotypes and sources of the strains for each PP, are listed.