Survival and plasmid transfer ability of Escherichia coli in wastewater

No differences were observed in the survival of plasmid-bearing and plasmid-free Escherichia coli strains in the course of a long-term survival process in wastewater, under both illuminated and non-illuminated conditions. While the CFU counts and the number of active cells decreased, the number of nucleoid-containing cells remained constant throughout the 30 days of experimentation. Visible light efficiently contributed to the reduction in culturability, and T-90 values were very different under illuminated and nonilluminated conditions. In the latter case the time necessary to reduce the culturability of a bacterial population by 90% was 27 days, while in the former it was only 1 day. Plasmid transfer was abundant, while the survival of donor and recipient cells was extensive. After 24 hr of survival in wastewater, transfer frequency values ranged from 5.92 x 10(-5) to 1.12 x 10(-2), depending on mating conditions. In the absence of illumination, the potential transfer abilities remained for survival periods of at least 20 days. Transfer assays between free and adhered cells were carried out by means of dialysis bags and submerged membrane diffusion chambers. Transfer frequency for adhered cells was greater than for free cells (2.80 x 10(-2) as opposed to 2.39 x 10(-3)).