Abstract: The present invention provides a plasmid pSOFLysK contained in the bacterial strain Lactococcus lactis NZ9800 referred herein as Lactococcus lactis NZ9800-pSOFLysK (subsequently designated Lactococcus lactis DPC6132) encoding anti-staphylococcal activity as deposited with DSMZ under accession No. ncimb 41409 and plasmids substantially similar thereto also providing anti-staphylococcal activity. In another aspect, the present invention provides a gene encoding an anti-staphylococcal protein, Lysin (LysK) as encoded by the plasmid pSOFLysK in Lactococcus lactis/VZ9800-pSOFLysK (subsequently designated Lactococcus lactis DPC6132). The recombinant lysine also has applications in diagnostics given its lytic mechanism.

Abstract: Plasmids carrying one or more genes which confer phage insensitivity upon Streptococcus lactis or Streptococcus lactis subsp. diacetylactis as well as Streptococcus cremoris bacteria in which the insensitivity is not destroyed at temperatures of up to 40.degree. C. are described. DNA fragments are also described which encode phage insensitivity. Such plasmids and DNA fragments are suitable for conferring phage insensitivity upon bacteria or food starter cultures containing bacteria.