Factors Influencing the Occurrence and the Fate of E. coli Population in Karst Hydrosystems
The persistence of Escherichia coli, a bacterial indicator of water quality, is relevant to assess the health risk associated with aquifer use for drinking water supplies. In order to investigate the fate of E. coli in a karst aquifer, populations of both viable and culturable E. coli were monitored, according to their settling velocities, for contrasting hydrological conditions. Solid-phase cytometry was carried out to quantify the viable E. coli, and both the genetic diversity and the resistance to antibiotics of E. coli were investigated. This study shows that: (i) at the sinkhole, the structure of the E. coli population varied with the hydrological conditions and land use; (ii) the input of E. coli strains resistant to antibiotics was linked to contamination of human origin during rainfall events; (iii) irrespective of the hydrological conditions, the karst system is a permanent reservoir of viable but non-culturable E. coli even when culturable E. coli became undetectable at the well; and (iv) following a rainfall event or during a dry period, both populations of culturable and viable but non-culturable E. coli are mainly associated with non-settleable particles, corresponding to organic or organo-mineral microflocs.
This study was based in part on the thesis work of Mehdy Ratajczak and Emilie Laroche. The authors thank Julie Gonand and Florian Van Dooren for technical assistance and Professor Robert Lafite for the settling experiments. This work was supported by the National Water Agency Seine Normandie and the Research Federation FR CNRS SCALE.
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