Efficacy and mechanisms of action of sodium hypochlorite on Pseudomonas aeruginosa PAO1 phage F116

The Pseudomonas aeruginosa PAO1 phage F116 was used to investigate the viri cidal activity and the mechanism of action of sodium hypochlorite. The bact eriophage was inactivated with a low concentration (0.0005% available chlor ine) of the biocide prepared in tap water but it was less sensitive to a so dium hypochlorite solution prepared in ultra-pure water (0.0075% available chlorine). For all the effective concentrations of sodium hypochlorite (i.e . producing at least 4 log reduction in phage titre), F116 was readily inac tivated within 30 s. Electron microscopical investigations of the phage par ticles challenged with sodium hypochlorite showed a wide variety of deleter ious effects, some of which have not been previously observed with other bi ocides. The wide range of structural alterations observed suggested that so dium hypochlorite has multiple target sites against F116 bacteriophage. A 3 0s exposure to sodium hypochlorite (0.001% available chlorine) produced sev ere damage, the number and severity of which increased with a higher concen tration (0.0075% available chlorine) and with a longer contact time. These observations suggested that sodium hypochlorite inactivated F116 bacterioph age by causing structural alterations to the phage head, tail and overall s tructure, hence possibly releasing the viral genome from damaged capsids in the surrounding media.