Thermal and chemical resistance of Lactobacillus casei and Lactobacillus paracasei bacteriophages

Aims: The survival of two collection Lactobacillus casei and L. paracasei bacteriophages when subjected to thermal and chemical treatments was investigated. Methods and Results: Thermal resistance was evaluated by heating phage suspensions at 63, 72 and 90degreesC in three different media [Tris-magnesium gelatin (TMG) buffer: 10 mmol l(-1) Tris-Cl, 10 mmol l(-1) MgSO4 and 0.1% w/v gelatin; Man Rogosa Sharpe (MRS) broth and reconstituted nonfat dry skim milk (RSM)]. A marked heat sensitivity was evident in both phages, as 15 min at 72degreesC was enough to completely inactivate (6 log(10) reduction) them. No clear influence was demonstrated by the suspension media. The phages also showed similar resistance to biocides. Peracetic acid and sodium hypochlorite (800 ppm) were the most effective ones, destroying the phages within 5 min. Concentrations of 75 and 100% ethanol were not suitable to inactivate phage particles even after 45 min. Isopropanol did not show an effect on phage viability. Conclusions: The data obtained in this work are important to design more effective control procedures in order to inactivate phages in dairy plants and laboratories. Significance and Impact of the Study: This work will contribute to enhance the background knowledge about phages of probiotic bacteria.