Use of peracetic acid as a disinfectant in a water-treatment plant: effect on the plasmid contents of Escherichia coli strains.

Total thermotolerant coliforms (TTC) and Escherichia coli strains were isolated from sewage from a treatment plant before and after peracetic acid (PAA) disinfection. The plasmid profiles of 120 E. coli strains were analyzed. Although PAA disinfection effectively reduced the number of TTC and E. coli strains, the percentage of E. coli strains containing plasmids was not statistically different among water samples. The sizes of the plasmids found ranged from < 3 kb to > 56 kb, but plasmids of between 3 and 5 kb were encountered most frequently.