Seasonal change and fate of coliphages infected to Escherichia coli O157:H7 in a wastewater treatment plant.

Seasonal change of virulent phage infected to two E. coli O157:H7 strains (O:157-phage) in the influent of a domestic wastewater treatment plant in the central part of Japan and fate of O:157-phage in the plant were monitored almost monthly from March 2001 to February 2002. Coliphage infected to nonpathogenic E. coli O157:H7 ATCC43888 (43888-phage) was detected for 1 year. On the other hand, phage infected to pathogenic E. coli O157:H7 EDL933 (EDL-phage) was detected intermittently. Concentration of EDL-phage was almost one-tenth of that of 43888-phage. The progressive decrease in phage concentration with the treatment steps was observed. No phage was detected in the supernatant from the secondary settling tank and effluent. PCR amplification of the Stx 2 gene that encodes Shiga toxin (Stx) was observed when O:157-phage concentration in the influent was high x10(3) PFU/ml order. Concentration and percentage of suspended O:157-phage decreased with the progress of the wastewater treatment. 933W phage, which encodes Stx 2 gene, was more fragile and sensitive to chlorination than T4 phage. However, addition of 0.02 mg/l chlorine, in conformance with the required concentration of the plant, did not affect the viability of T4 and 933 W phages. On the other hand, 1mg/l chlorine inactivated the 933 W phage significantly.