Effect of gamma irradiation on bacteriophages used as viral indicators

This study aimed to examine the susceptibility of indicator bacteriophages towards γ-radiation to evaluate their appropriateness as viral indicators for water quality control. The effects of γ-radiation on naturally occurring somatic coliphages, F-specific coliphages and Escherichia coli were examined in raw sewage and sewage sludge. As well, the effects of radiation on bacteriophages ΦX174 and MS2, and E. coli all grown in the laboratory and seeded in distilled water, autoclaved raw sewage and a 1% peptone solution were evaluated. The inactivation of E. coli was fairly similar in all matrices. In contrast, inactivation of bacteriophages was significantly greater in distilled water than in the other matrices. These results showed the great influence of the matrix characteristics on virus inactivation. Somatic coliphages in raw sewage and sewage sludge and ΦX174 in autoclaved sewage were inactivated similarly and were far more resistant than F-specific coliphages, MS2 and E. coli. As well, F-specific RNA bacteriophages in raw sewage and sewage sludge and MS2 in autoclaved sewage were inactivated similarly and were more resistant than E. coli. In contrast, MS2 was more susceptible to γ-radiation than E. coli in distilled water. Our results showed that ΦX174 is a suitable indicator for estimating virus inactivation by γ-irradiation and corroborate the use of somatic coliphages to survey the viral quality of treated water and sludges.