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

MERCANTI, DIEGO JAVIER; GUGLIELMOTTI, DANIELA MARTA; REINHEIMER, JORGE ALBERTO; QUIBERONI, ANDREA DEL LUJÁN

Buenos Aires

Congreso; XIII Congreso Argentino de Ciencia y Tecnología de los Alimentos (CYTAL); 2011

Asociación Argentina de Tecnólogos Alimentarios

Bacteriophages are ubiquitous in dairy plants, causing fermentation failures with large economic losses. Raw milk constitutes their main source, either as free virions or as inducible prophages within dairy strains. Hence, bacteriophages are impossible to eradicate from dairy plants. Use of bacteriophage insensitive mutants presents drawbacks (narrow phage specificity, reversion of the phenotype) and strain rotation, though useful for traditional starters, is not suitable for probiotic bacteria with strain-specific traits. Physical and/or chemical treatments will always be necessary to counteract this problem. In this work, temperate bacteriophages iLp84 and iLp1308, isolated after mitomycin C induction of Lactobacillus paracasei strains 84 and 1308, respectively, were tested for their resistance to several physical and chemical treatments of application in dairy industry. Lb. paracasei strains INL3 and A14 were used as host of iLp84 and iLp1308, respectively. Both phages were tested for their survival at different temperatures of storage, and after thermal treatments of 63ºC, 72ºC and 90ºC in three different media for up to 45 min. Their resistance to high pressure homogenization (HPH, 100 MPa) and to either classic (ethanol, sodium hypochlorite and peracetic acid) or five 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), was also studied. Phage enumerations were carried out immediately before and after incubation with each biocide (or pass through a high-pressure homogenizer) by the double-layer plate titration method. Both phages showed very good survival rates during long-term (1 year) storage at 4ºC, ‑20ºC and ‑80ºC, but a fast decay (between 5 and 6 log orders) was observed after six months of room temperature storage (25ºC). Phage iLp1308 showed higher thermal resistance than iLp84, though none was detected after 2 min at 90ºC. Slight variations among different suspension media were observed only for iLp1308. Best chemical inactivation was accomplished by using peracetic acid or biocides A, C and E, followed by sodium hypochlorite, whereas ethanol was less efficient and biocides B and D had no effect on phage viability. Phage iLp1308 was more resistant than iLp84 to biocide A, but the opposite was true for sodium hypochlorite. Viability of phages iLp84 and iLp1308 was diminished 5 and 4 log orders (respectively) after 8 passes at a pressure of 100 MPa, demonstrating a similar resistance to previously reported phages of Lb. paracasei and Lb. plantarum, but considerably higher than phages infecting other genera of lactic acid bacteria. Briefly, our results would help to select better chemical agents and physical treatments to effectively fight against phage infections in dairy plants.