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 proces s in wastewater, under both illuminated and non-illuminated conditions. Whi le the CFU counts and the number of active cells decreased, the number of n ucleoid-containing cells remained constant throughout the 30 days of experi mentation. Visible light efficiently contributed to the reduction in cultur ability, and T-90 values were very different under illuminated and nonillum inated conditions. In the latter case the time necessary to reduce the cult urability 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 do nor and recipient cells was extensive. After 24 hr of survival in wastewate r, transfer frequency values ranged from 5.92 x 10(-5) to 1.12 x 10(-2), de pending on mating conditions. In the absence of illumination, the potential transfer abilities remained for survival periods of at least 20 days. Tran sfer assays between free and adhered cells were carried out by means of dia lysis bags and submerged membrane diffusion chambers. Transfer frequency fo r adhered cells was greater than for free cells (2.80 x 10(-2) as opposed t o 2.39 x 10(-3)).