Technological Properties of Lactococcus lactis subsp. lactis I23 Isolated from Nigerian Beef and Characterization of Bacteriocin Produced by It

Aim: The present study reports the phenotypic and molecular characterization of Lactococcus strains isolated from Nigerian beef. The technological properties of selected strains were evaluated in order to test their suitability as candidates of starter cultures for food preservation.

Study Design: Experimental microbiological testing.

Place and Duration of Study: Microbiology Department, University of Ibadan, Nigeria and Division of Food Sciences, The University of Nottingham, UK; between January 2005 and February 2009.

Methodology: Phenotypic method was adopted in the initial characterization of the presumptive Lactococcus strains which were later characterized using pulsed field gel electrophoresis. The use of 16S rDNA sequencing was adopted in the full identification of selected strains. High performance liquid chromatography and Gas chromatography were employed in determining production of organic acids and diacetyl respectively by the strains of Lactococcus. Testing and identification of bacteriocin production by the strains were observed using in vitro and polymerase chain reaction methods. The antimicrobial activities of the strains were evaluated against known spoilage and pathogenic organisms of food origin.

Results: Three strains, Lc. lactis L11, Lc. lactis subsp. lactis I23 and Lc. lactis subsp. hordinae E91 showed better production of diacetyl and lactic acid than others; concentrations in excess of 31.15 µg/10-7cfu and 17.56 g/107cfu at 18 and 24 h of incubation were recorded for the respective compounds. Result of their antimicrobial activities indicates that varying levels of inhibition were recorded against the spoilage/pathogenic organisms; however no inhibition was recorded against Brochothrix thermosphacta except by Lc. lactis subsp lactis I23 which was shown to encode gene for production of bacteriocin, nisin. The nucleotide sequence of the bacteriocin was deposited at the genBank under accession number EU667387.

Conclusion: The ability of the three Lactococcus strains to combat spoilage and pathogenic organisms could help promote safety in food processing and preservation in Nigeria; moreover, production of bacteriocin by Lc. lactis subsp. lactis I23 may confer added advantage during choice of candidacy for starter cultures in food biopreservation.