[Screening, isolation and identification of nisin resistance determinant gene in strains of Lactococcus lactis].

OBJECTIVE: To isolate and identify nisin resistance determinant (NSR) gene from Lactococcus lactis.
METHODS: The Lactococcus lactis strains harboring NSR gene were isolated from different milk samples by selective culture supplemented with nisin and confirmed by PCR detection of 16S rRNA. Nisin resistance determinant gene was determined by PCR amplification, enzyme digestion and sequencing.
RESULTS: Thirty nisin-resistant Lactococcus lactis strains from fresh milk samples were obtained. Three of these strains contained NSR gene of about 1000 bp as determined by agarose gel electrophoresis and further confirmed by enzyme digestion and sequence analysis. The NSR gene was located on the plasmid of Lactococcus lactis.
CONCLUSION: Complete NSR gene, located on the bacterial plasmid, has been successfully isolated from nisin-resistant Lactococcus lactis strains from fresh milk.