Resistance of two temperate Lactobacillus paracasei bacteriophages to high pressure homogenization, thermal treatments and chemical biocides of industrial application

Temperate bacteriophages phi iLp84 and phi iLp1308, previously isolated from mitomycin C-induction of Lactobacillus paracasei strains 84 and CNRZ1308, respectively, were tested for their resistance to several physical and chemical treatments applied in dairy industry. Long-term survival at 4 degrees C, -20 degrees C and -80 degrees C, resistance to either thermal treatments of 63 degrees C, 72 degrees C and 90 degrees C, high pressure homogenization (HPH, 100 MPa) or classic (ethanol, sodium hypochlorite and peracetic acid) and new commercial sanitizers, namely A (quaternary ammonium chloride), B (hydrogen peroxide, peracetic acid and peroctanoic acid), C (alkaline chloride foam), D (p-toluensulfonchloroamide, sodium salt) and E (ethoxylated nonylphenol and phosphoric acid), were determined. Phages were almost completely inactivated after eight months of storage at 25 degrees C, but viability was not affected at 4 degrees C, -20 degrees C or -80 degrees C. Both phages tolerated well HPH treatments. Phage iLp1308 showed higher thermal resistance than phi iLp84, but neither resisted 90 degrees C for 2 min. Best chemical inactivation was accomplished using peracetic acid or biocides A, C and E, whereas biocides B and D were completely ineffective. These results help to improve selection of chemical agents and physical treatments to effectively fight against phage infections in dairy plants. (C) 2011 Elsevier Ltd. All rights reserved.