Bacteriophages on dairy foods.

This review focuses on the impact of bacteriophages on the manufacture of dairy foods. Firstly, the impact of phages of lactic acid bacteria in the dairy industry, where they are considered enemies, is discussed. The sources of phage contamination in dairy plants are detailed, with special emphasis on the rise of phage infections related to the growing use of cheese whey as ingredient. Other topics include traditional and new methods of phage detection, quantification and monitoring, and strategies of phage control in dairy plants, either of physical, chemical or biological nature. Finally, the use of phages or purified phage enzymes as allies to control pathogenic bacteria in the food industry is reviewed.

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

Temperate bacteriophages ф iLp84 and ф 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 °C, -20 °C and -80 °C, resistance to either thermal treatments of 63 °C, 72 °C and 90 °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 °C, but viability was not affected at 4 °C, -20 °C or -80 °C. Both phages tolerated well HPH treatments. Phage iLp1308 showed higher thermal resistance than ф iLp84, but neither resisted 90 °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.

Isolation and phenotypic characterization of Lactobacillus casei and Lactobacillus paracasei bacteriophage-resistant mutants.

AIMS: To isolate and characterize bacterial strains derived from Lactobacillus casei and Lactobacillus paracasei strains and resistant to phage MLC-A. METHODS AND RESULTS: Two of nine assayed strains rendered resistant mutants with recovery efficiencies of 83% (Lact. paracasei ATCC 27092) and 100% (Lact. casei ATCC 27139). DNA similarity coefficients (RAPD-PCR) confirmed that no significant genetic changes occurred while obtaining resistant mutants. Neither parent nor mutant strains spontaneously released phages. Phage-resistant mutants were tested against phages PL-1, J-1, A2 and MLC-A8. Lactobacillus casei ATCC 27092 mutants showed, overall, lower phage resistance than Lact. paracasei ATCC 27092 ones, but still higher than that of the parent strain. Lactobacillus paracasei ATCC 27092 mutants moderately adsorbed phage MLC-A only in calcium presence, although their parent strain successfully did it with or without calcium. Adsorption rates for Lact. casei ATCC 27139 and its mutants were highly influenced by calcium. Again, phage adsorption was higher on the original strain. CONCLUSIONS: Several isolates derived from two Lact. casei and Lact. paracasei strains showed resistance to phage MLC-A but also to other Lact. casei and Lact. paracasei phages. SIGNIFICANCE AND IMPACT OF THE STUDY: This study highlights isolation of spontaneous bacteriophage-resistant mutants from Lact. casei and Lact. paracasei as a good choice for use in industrial rotation schemes.

Diversity among Lactobacillus paracasei phages isolated from a probiotic dairy product plant.

AIMS: To evaluate the phage diversity in the environment of a dairy industry which manufactures a product fermented with a probiotic strain of Lactobacillus paracasei. METHODS AND RESULTS: Twenty-two Lact. paracasei phages were isolated from an industrial plant that manufactures a probiotic dairy product. Among them, six phages were selected based on restriction profiles, and two phages because of their notable thermal resistance during sample processing. Their morphology, host range, calcium dependency and thermal resistance were investigated. All phages belonged to the Siphoviridae family (B1 morphotype), were specific for Lact. casei and paracasei strains showing identical host spectrum, and only one phage was independent of calcium for completing its lytic cycle. Some of the phages showed an extraordinary thermal resistance and were protected by a commercial medium and milk. CONCLUSIONS: Phage diversity in a probiotic product manufacture was generated to a similar or greater extent than during traditional yogurt or cheese making. SIGNIFICANCE AND IMPACT OF THE STUDY: This work emphasizes probiotic phage infections as a new ecological situation beyond yogurt or cheese manufactures, where the balanced coexistence between phages and strains should be directed toward a favourable state, thus achieving a successful fermentation.