Effect of weak acid hypochlorous solution on selected viruses and bacteria of laboratory rodents

Abstract

Weak acid hypochlorous solution (WAHS) is known to have efficacy for inactivating pathogens and to be relatively safe with respect to the live body. Based on these advantages, many animal facilities have recently been introducing WAHS for daily cleaning of animal houses. In this study, we determined the effect of WAHS in inactivating specific pathogens of laboratory rodents and pathogens of opportunistic infection. WAHS with an actual chloride concentration of 60 ppm and a pH value of 6.0 was generated using purpose-built equipment. One volume of mouse hepatitis virus (MHV), Sendai virus, lymphocytic choriomeningitis virus, Bordetella bronchiseptica, Pasteurella pneumotropica, Corynebacterium kutscheri, Staphylococcus aureus, and Pseudomonas aeruginosa was mixed with 9 or 99 volumes of WAHS (×10 and ×100 reaction) for various periods (0.5, 1, and 5 min) at 25°C. After incubation, the remaining infectious viruses and live bacteria were determined by plaque assay or culture. In the ×100 reaction mixture, infectious viruses and live bacteria could not be detected for any of the pathogens examined even with the 0.5-min incubation. However, the effects for MHV, B. bronchiseptica, and P. aeruginosa were variable in the ×10 reaction mixture with the 0.5- and 1-min incubations. Sufficient effects were obtained by elongation of the reaction time to 5 min. In the case of MHV, reducing organic substances in the virus stock resulted in the WAHS being completely effective. WAHS is recommended for daily cleaning in animal facilities but should be used properly in order to obtain a sufficient effect, which includes such things as using a large enough volume to reduce effects of organic substances.

Figures

Fig. 1.

Antiviral effects of disinfectants in the ×10 reaction mixture. (a) Effect of WAHS. For MHV, the results of all reaction times are shown as means of 7 experiments. (b) Effect of 0.03% sodium hypochlorite. (c) Effect of 70% ethanol. As a control, bacterial solutions were mixed with the final ×10 sterilized PBS and reacted for 5 min at 25°C. The culture medium for the MHV stock was MEM containing 10% FBS and 10% TPB. After reaction, infectious viruses were titrated in culture cells. The effect on HVJ was determined only using WAHS. The vertical bars show the viable bacteria counts, and 2.0 log10 represents the detection limit. Asterisks indicate values that are less than the detection limit.

Fig. 2.

Effect of medium conditions for MHV viral stock and reaction ratio on the efficacy of WAHS. (a) The culture medium for MHV stock was changed to MEM containing 2% FBS without TPB. (b) Viral solution was mixed with the final ×100 volume of WAHS. Asterisks indicate values that are less than the detection limit.

Fig. 3.

Antibacterial effects of disinfectants in the ×10 reaction mixture. (a) Effect of WAHS. For B. bronchiseptica and P. aeruginosa, the results for 0.5 and 1 min are shown as means of 6 experiments. (b) 0.03% sodium hypochlorite. For B. bronchiseptica, the results for 0.5 min are shown as the mean of 5 experiments. (c) Effect of 70% ethanol. As a control, bacterial solutions were mixed with the final ×10 sterilized physiological saline and reacted for 5 min at 25°C. After reaction, viable bacteria were cultured on agars. The vertical bars show viable bacteria counts, and 2.0 log10 represents the detection limit. Asterisks indicate values that are less than the detection limit.

Fig. 4.

Antibacterial effect of disinfectants in the ×100 reaction mixture. (a) Effect of WAHS. (b) Effect of 0.03% sodium hypochlorite. As controls, bacterial solutions were mixed with the final ×100 sterilized physiological saline and reacted for 5 min at 25°C. After reaction, viable bacteria were cultured on agars. The vertical bars show viable bacteria counts, and 2.0 log10 represents the detection limit. Asterisks indicate values that are less than the detection limit.