Influence of hydrological conditions on the Escherichia coli population structure in the water of a creek on a rural watershed

Mehdy Ratajczak,Emilie Laroche,Thierry Berthe,Erick Denamur,Barbara Pawlak,Olivier Clermont,Fabienne Petit

doi:10.1186/1471-2180-10-222

Abstract

BackgroundEscherichia coli is a commensal bacterium of the gastro-intestinal tract of human and vertebrate animals, although the aquatic environment could be a secondary habitat. The aim of this study was to investigate the effect of hydrological conditions on the structure of the E. coli population in the water of a creek on a small rural watershed in France composed of pasture and with human occupation.ResultsIt became apparent, after studying the distribution in the four main E. coli phylo-groups (A, B1, B2, D), the presence of the hly (hemolysin) gene and the antibiotic resistance pattern, that the E. coli population structure was modified not only by the hydrological conditions (dry versus wet periods, rainfall events), but also by how the watershed was used (presence or absence of cattle). Isolates of the B1 phylo-group devoid of hly and sensitive to antibiotics were particularly abundant during the dry period. During the wet period and the rainfall events, contamination from human sources was predominantly characterized by strains of the A phylo-group, whereas contamination by cattle mainly involved B1 phylo-group strains resistant to antibiotics and exhibiting hly. As E. coli B1 was the main phylo-group isolated in water, the diversity of 112 E. coli B1 isolates was further investigated by studying uidA alleles (beta-D-glucuronidase), the presence of hly, the O-type, and antibiotic resistance. Among the forty epidemiolgical types (ETs) identified, five E. coli B1 ETs were more abundant in slightly contaminated water.ConclusionsThe structure of an E. coli population in water is not stable, but depends on the hydrological conditions and on current use of the land on the watershed. In our study it was the ratio of A to B1 phylo-groups that changed. However, a set of B1 phylo-group isolates seems to be persistent in water, strengthening the hypothesis that they may correspond to specifically adapted strains.

Highlights

Escherichia coli is a commensal bacterium of the gastro-intestinal tract of human and vertebrate animals, the aquatic environment could be a secondary habitat
E. coli population structure in creek water in relation to hydrological conditions and watershed land use E. coli were enumerated and the population structure analyzed by phylo-grouping in three sets of samples collected under different hydrological and agricultural land-use conditions (Table 1)
This structure argues for contamination by E. coli B1 isolates that are better adapted to the aquatic environment [15], rather than for residual bovine fecal contamination, as the isolates were devoid of the hly gene and sensitive to all antibiotics [35,36]

Summary

Introduction

Escherichia coli is a commensal bacterium of the gastro-intestinal tract of human and vertebrate animals, the aquatic environment could be a secondary habitat. The diversity of E. coli populations in their secondary habitats has been studied by analyzing the sequences of the gene uidA [19,20], palindromic repetitive sequences [21,22], ribotypes [23], and profiles of antibiotic resistance [24,25]. Using these methods, the dynamics of E. coli populations have been investigated and, in some cases, it has been possible to discriminate between the human or animal origin of the contamination

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