FATE OF ESCHERICHIA-COLI EXPERIMENTALLY INJECTED IN A DRINKING-WATER DISTRIBUTION PILOT SYSTEM

Detection of coliforms and E. call in drinking water distribution syst ems can be explained by accidental contaminations and/or growth of the se bacteria in the network. This last point still remaining debatable, an experiment was carried out with two E. call strains (E. coil O126: B16 and one isolated from a drinking water distribution system) separa tely injected in a drinking water distribution pilot plant continuousl y fed with drinking water. The work aimed to study (i) the partition o f the injected bacteria between the water phase and the indigenous bio film phase and (ii) the kinetic of disappearance or growth of these ba cteria. Depending on the strain, 1-50% of injected bacteria adsorbed w ithin a few hours to the indigenous bacterial biofilm. During the firs t 5-7 days, both E. coil populations behaved similarly: the total numb er of injected bacteria decreased more quickly than the theoretical wa shout (death, lysis, predation,...). Then the number of these bacteria slowly increased and at day 9-12, the number of recoverable injected bacteria became higher than the predictable number calculated from the theoretical washout. This result clearly proves that both E. coli str ains are able to grow at 20 degrees C in the absence of residual chlor ine in a distribution network system largely colonized with an autocht honous population. However, colonization of the network by E. coli str ains was only partial and transient. Copyright (C) 1996 Elsevier Scien ce Ltd