Summary This is the first study on lactic acid bacteria bacteriophages isolated from dairy plants in Slovenia. Over a period of 2 years, thirteen lactococcal phages were isolated from the whey samples taken in three dairy plants. Phages were characterized by morphological properties, host range, restriction patterns, genome size and similarity of phage protein genes. All phages belonged to the Siphoviridae family. Five phages had prolate heads (52–61 × 40–52 nm) and 85–120 nm long non‐contractile tails (morphotype B2). Eight phages had small isometric heads (46–63 nm in diameter) and long non‐contractile tails (morphotype B1). The phages with the prolate heads showed a broader host range than the small isometric‐headed phages. The genome sizes of prolate phages were estimated between 15.9 and 16.3 kb while the genome sizes of small isometric‐headed phages were between 20.0 and 39.9 kb. Based on DNA restriction patterns, genome sizes and multiplex PCR analysis prolate phages were classified into the c2 group and were similar to the phage type c6A while all of the phages with small isometric heads were found to be related to the phage species 936.

Three different bacterial defence mechanisms were identified in the seventeen Lactococcus lactis isolates from starter cultures in three Slovenian dairy plants. Isolates MB18, KR7, PT4, PT13 and PT19 inhibited phage adsorption by means of exopolysaccharides production. The most extensive polysaccharides production was detected in PT19 isolate, which was susceptible only to phage UPT19. Eight isolates exhibited nuclease activity, and seven of them were susceptible up to four phages out of thirteen from our collection. Eight isolates possessed the abiB gene, fourteen isolates abiH, two isolates abiJ and one isolate abiQ. Isolates PT27 and PT28 possessed AbiB, AbiH and AbiJ mechanisms as well as inhibition of phage adsorption. Isolate MB18, which was susceptible to one phage only, possessed the abiQ gene, nuclease activity and ability to prevent adsorption of most phages. Isolates PT67 and PT70, possessing only AbiH mechanism, were susceptible to only two phages.