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.