Comparative analysis of Streptococcus thermophilus bacteriophages isolated from a yogurt industrial plant Original Research Article

Phage infections represent a serious problem in the dairy industry where Streptococcus thermophilus is largely used as a starter in yogurt and cheese manufactures. The goal of the present study was to determine the permanence in the plant and the diversity among 11 lytic S. thermophilus phages isolated from batches with acidifying problems in an Argentinian yogurt factory between 1998 and 2000. Phages were characterized by their morphology, restriction patterns, DNA–DNA hybridization analysis and host range. Restriction analysis of their genomes allow us to arrange them in six groups, while host spectrum using 20 S. thermophilus strains revealed five groups. A strong relationship among phages was observed when Southern and Dot blot hybridizations were performed. Sensitive strains were not lysogenic since neither of them was induced by mitomycin C. Our results, concerning the diversity, monitoring and permanence of phages in the dairy plant environment, complement the findings of authors that cover phage collections from European countries.