Assessment of Bacillus subtilis spores as a possible bioindicator for evaluation of the microbicidal efficacy of radiation processing of water.

Gamma and electron-beam irradiation of Bacillus subtilis spores suspended in different types of water was studied to evaluate the inactivation of the spores and assess their possible use as a bioindicator for radiation processing. We found that the inactivation proceeded endogenously, being dose-rate-dependent and affected by oxygen. The radiation resistance of the suspended spores was found to be rather high; therefore, B. subtilis spores used as a bioindicator for efficiency of water treatment by radiation under practical conditions might result in the spores being overly conservative surrogates for pathogenic microorganisms. Moreover, the doserate dependency impedes the use of the spores as a bioindicator. Thus, B. subtilis spores cannot be recommended as a bioindicator for evaluation of the microbicidal efficacy of ionizing radiation processing of water.

Bacteriophages as viral indicators for radiation processing of water: a chemical approach.

Inactivation of the bacteriophages PHI X 174 (somatic coliphage), MS2 (F-specific coliphage) and B40-8 (phage infecting Bacteroides fragilis) suspended in tap water was studied applying gamma and electron beam irradiation as well. PHI X 174 phage was found to be a suitable viral indicator for water disinfection by means of ionizing radiation. The nutrient broths introduced simultaneously with the bacteriophages into the water when it is spiked with the phages for the experiments did not significantly change the scavenging capacity of the water matrix. No dose rate effect was observed with MS2 and B40-8 phages but PHI X 174 phage showed a clear dose rate effect. It was found that in water MS2 phage is significantly more sensitive to ionizing radiation than Escherichia coli.