[The problem in the reactivation of microorganisms on evaluating the efficacy of water disinfectants]

The investigation deals with the topical problem of whether bacterial viability and properties may be restored after the achieved bacteriostatic effect of water disinfection, which reduces the reliability of the control and adequate assessment of its epidemic safety. The objective of the investigation was to study whether bacteria might be reactivated in the estimation of water disinfection with guanidine-containing agents as an alternative to chlorine. Experiments were carried out on the waters from model water reservoirs, by simulating water contamination with residential waste waters and on the natural water from the Moscow River, by reproducing the purification conditions: coagulation, filtration, disinfection with a binary mixture of polyhexamethyleneguanidine hydrochloride and quaternary ammonium compound. The experimental studies of the efficacy of the binary agent against indicator, opportunistic, and pathogenic bacteria indicated that the viability of bacterial cells might be reactivated and restored after water disinfection and cell multiplication upon further exposure. Microorganisms that had the greatest capacity for reactivation after use of the binary agent, as evidenced by the group values of the total number of saprophytes (microbial number) at 37 degrees C, coliform bacteria, and Pseudomonas aeruginosa, were identified. The findings show it necessary to consider reactivation processes in the evaluation of novel disinfectants, which requires a supplemented procedure for obligatorily estimating their exposure 24 hours after use of a reagent.