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Aims. Identification of Lactococcus lactis ssp. and Streptococcus thermоphilus virulent bacteriophages isolated in dairy processing plants of Ukraine. Methods. The morphology of the viral particles was studied by transmission electron microscopy. Identification of structural proteins of phage was carried out by SDS-PAGE. The taxonomic position of phages was determined by multiplex PCR. Results. We presented results of the study of biological properties of 21 lactic acid bacteria phages isolated in dairy processing plants of Ukraine during 2007-2017. It was shown that phages had long, noncontractile tails, and therefore were classified to Caudovirales order, Siphoviridae family. Phages of L. lactis ssp. differed by head shape: phages with isometric heads of B1 morphotype and phages with prolate heads of B2 morphotype were detected. All analyzed S. thermophilus phages displayed specific morphology for B1 morphotype. Some of them had atypical shorter tails of 133-137 nm in length, with basal plates without globular appendages. Lytic activity spectrum of various phages was investigated and it was defined an absence of correlations between the indices of phages lytic activity and viral particles morphology. Phages of L. lactis ssp. were very heterogeneous on the basis of protein composition and formed three groups. Thus, с2 phages species differed by the fact that contained major proteins with greater molecular weights 30, 55 and 72 kDa. Phages of S. thermoрhilus contained two or three major proteins with the molecular weights of 33 and 27 kDa; 42, 26, and 15 kDa, respectively. Conclusions. Bacteriophages of L. lactis ssp. according to their morphology, protein profile and PCR results were identified to species: 1) 38.1 % of phages belong to species 936; 2) to the species P335 – 9.5 %; 3) to the species c2 – 19.0 %. Phages S. thermophilus were identified to three groups: 1) the group of cos-type amounted to 14.3 % of the total; 2) the group of pac-type – 9.5 % аnd 3) 987 group – 9.5 % of phages.

Bacteriophages of Lactococcus lactis ssp. and Streptococcus thermоphilus Isolated in Dairy Processing Plants of Ukraine