The long-term survival of Escherichia coli in river water.

Escherichia coli introduced into autoclaved filtered river water survived for up to 260 d at temperatures from 4 degrees to 25 degrees C with no loss of viability. Survival times were less in water which was only filtered through either a Whatman filter paper or a 0.45 micron Millipore filter or in untreated water, suggesting that competition with the natural microbial flora of the water was the primary factor in the disappearance of the introduced bacteria. Survival was also dependent upon temperature with survival at 4 degrees C greater than 15 degrees C greater than 25 degrees C greater than 37 degrees C for any water sample. Direct counts showed that bacterial cells did not disappear as the viable count decreased. The possession of the antibiotic resistance plasmids, R1drd-19 or R144-3, did not enhance survival nor cause a faster rate of decay, indicating that the metabolic burden imposed by a plasmid was not a factor in survival under starvation conditions. There was no evidence of transfer of either plasmid at 15 degrees C or of loss of plasmid function during starvation.