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Open Access Research article

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

Mehdy Ratajczak1*, Emilie Laroche1, Thierry Berthe1, Olivier Clermont2, Barbara Pawlak1, Erick Denamur2 and Fabienne Petit1

Author Affiliations

1 Laboratoire M2C, Université de Rouen, CNRS UMR 6143, FED SCALE 4116, 76821 Mont Saint Aignan, France

2 Laboratoire Ecologie et évolution des microorganismes, Université Paris 7 Denis Diderot and INSERM U722, 75018 Paris, France

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BMC Microbiology 2010, 10:222  doi:10.1186/1471-2180-10-222

Published: 19 August 2010

Abstract

Background

Escherichia 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.

Results

It 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.

Conclusions

The 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.