Abstract:
A total of 115 lactic acid bacteria were isolated from 23 samples of raw milk and Thai fermented sausages (nham). The bacteria were tested by agar well diffusion method for inhibition activity. The results showed that supernatants of 4 lactic acid bacteria produced inhibition zone against 3 indicator bacteria, Lactobacillus plantarum TISTR 850, Pediococcus pentosaceus TISTR 374 and Propionibacterium freundenreichii TISTR 446. Confirmation of nisin producing strains were performed by Polymerase Chain Reaction (PCR) using nisin specific primers. Two bacterial isolates MF2 and MF3, showed a specific PCR product with expected size of 300 bp. PCR product from MF2 selected for further analysis. Nucleotide sequence of PCR product revealed an open reading fame (ORF) of 171 bp and encoded a protein of 57 amino acids with expected molecular weight of 59 KDa. Nucleotide sequence identity of PCR product compared with nisA gene and nisZ gene from Lactococcus lactis subsp. lactis were 99%, respectively. The amino acid sequence identity compared with nisin A and nisin Z precursor were 100%, respectively. Amino acid analysis showed that PCR product encoded nisin A as indicated by histidine residue at position 27. Based on its morphological characteristics and biochemical analysis together with 16S rRNA sequence, MF2 was classified as L. lactis subsp. lactis. Gene involving in nisin biosynthesis was isolated from L. lactis subsp. lactis MF2. Nucleotide sequences of the cloned fragment from L. lactis subsp. lactis MF2 of 700 bp shows 100% homology to lciB gene that involving of lactococcin B immunity biosynthesis.