Hypochlorite inactivation kinetics of lactococcal bacteriophages

Ten heat-resistant lactococcal phages in M17 broth were inactivated by exposure to a range of different hypochlorite concentrations (2000–5000 mg l−1). Deviations from first-order kinetics as sigmoidal shapes were observed in the survival curves of all bacteriophages. Therefore, an empirical model with four parameters was used to describe hypochlorite inactivation. The model provided good fit for all phages; however, it was observed that there was a high correlation between the parameters of this model. That is why, the number of parameters was reduced from four to two with a slight loss of goodness-of-fit and this reduced model produced fits comparable to the original model. Alternative D and z values were also proposed for the model. By comparing the times necessary to reduce the number of phages six- or seven-logs, the most hypochlorite-resistant phages were found as: φpld67 37, φpll47 21 and φpld66 36. Demonstration of this model may also be used for other bacteriophages inactivated by other biocides.