Thermal and chemical inactivation of lactococcal bacteriophages

Ten lactococcal bacteriophages in M17 broth were treated by heat (72 °C, 15 min and 90 °C, 5 min), ethanol and isopropanol at concentrations of 10%, 50%, 75% and 100% (v/v). The heat treatments were not sufficient to inactivate all the bacteriophages studied whereas ethanol, which was also more efficient biocide than isopropanol, at a concentration of 75% could inactivate all the phages in 1 min. The 50% and 75% of ethanol were more effective than 100%, which was also observed for isopropanol. Survival curves’ deviations from linearity as sigmoidal shapes could be described via an empirical model with four parameters. The parameters of the model could be reduced from four to two with a slight loss of goodness-of-fit. The reduced model also provided good fit to describe the isopropanol inactivation kinetics of the phages at concentrations of 50% and 75%. This demonstration may also be a useful tool for further inactivation studies in which ethanol or other biocides are used with sufficient survival data points at selected time intervals. Although more studies should be carried out with different phages, this study confirmed the lethal effect of ethanol, commonly used to disinfect utensils and laboratory equipment, on lactoccocal bacteriophages.