Factors Influencing the Occurrence and the Fate of E. coli Population in Karst Hydrosystems
Résumé
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.