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

• Main Authors: Ratajczak Mehdy, Laroche Emilie, Berthe Thierry, Clermont Olivier, Pawlak Barbara, Denamur Erick, Petit Fabienne
• Format: Article
• Language: English
• Published: BMC 2010-08-01
• Series: BMC Microbiology
• Online Access: http://www.biomedcentral.com/1471-2180/10/222

<p>Abstract</p> <p>Background</p> <p><it>Escherichia coli </it>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 <it>E. coli </it>population in the water of a creek on a small rural watershed in France composed of pasture and with human occupation.</p> <p>Results</p> <p>It became apparent, after studying the distribution in the four main <it>E. coli </it>phylo-groups (A, B1, B2, D), the presence of the <it>hly </it>(hemolysin) gene and the antibiotic resistance pattern, that the <it>E. coli </it>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 <it>hly </it>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 <it>hly</it>. As <it>E. coli </it>B1 was the main phylo-group isolated in water, the diversity of 112 <it>E. coli </it>B1 isolates was further investigated by studying <it>uidA </it>alleles (beta-D-glucuronidase), the presence of <it>hly</it>, the O-type, and antibiotic resistance. Among the forty epidemiolgical types (ETs) identified, five <it>E. coli </it>B1 ETs were more abundant in slightly contaminated water.</p> <p>Conclusions</p> <p>The structure of an <it>E. coli </it>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.</p>