Comparison of bacteriophages for use in iodine inactivation: Batch and continuous flow studies

Inactivation rates in batch studies for four commonly used surrogate bacteriophages were measured in stable aqueous iodine solutions for the purpose of determining which was the most suited to evaluate iodine disinfection efficacy in batch and continuous flow conditions. Two types of group Leviviridae bacteriophages were used, Type I (MS2) and Type II (GA), along with group Microviridae, Phi-X174, and group Tectiviridae, PRD1. Inactivation was compared at iodine doses of 1.0-1.5 mg I₂/l. MS2 was the most susceptible to iodine inactivation of the four phages tested. Inactivation of naked, icosahedral bacteriophages, MS2 and Phi-X174 demonstrated removals to below detection limits (>99.99%) in less than 10 min. Lipid-containing PRD1 and F+ssRNA GA bacteriophages demonstrated the greatest iodine resistance in batch experiments with an average of 1.82 logs of inactivation (98.5%) after 60 min and 1.05 logs of inactivation (91.1%) after 30 min respectively. Similarly, in continuous flow studies through pentaiodide quaternary ammonium strong base resin, MS2, GA and Phi-X174 were more strongly inactivated than PRD1. The lipid component of PRD1 is thought to enhance resistance to iodine over non-lipid-containing bacteriophages by protecting easily oxidized groups on the protein capsid, but further research is needed before proving this hypothesis. The results from this research may provide a surrogate standard for more rigorous and developed research into the mode of iodine disinfection and its inactivation kinetics.