Antagonistic lactic acid bacteria isolated from goat milk and identification of a novel nisin variant Lactococcus lactis

Luís Nero,Luana Perin

doi:10.1186/1471-2180-14-36

Abstract

BackgroundThe raw goat milk microbiota is considered a good source of novel bacteriocinogenic lactic acid bacteria (LAB) strains that can be exploited as an alternative for use as biopreservatives in foods. The constant demand for such alternative tools justifies studies that investigate the antimicrobial potential of such strains.ResultsThe obtained data identified a predominance of Lactococcus and Enterococcus strains in raw goat milk microbiota with antimicrobial activity against Listeria monocytogenes ATCC 7644. Enzymatic assays confirmed the bacteriocinogenic nature of the antimicrobial substances produced by the isolated strains, and PCR reactions detected a variety of bacteriocin-related genes in their genomes. Rep-PCR identified broad genetic variability among the Enterococcus isolates, and close relations between the Lactococcus strains. The sequencing of PCR products from nis-positive Lactococcus allowed the identification of a predicted nisin variant not previously described and possessing a wide inhibitory spectrum.ConclusionsRaw goat milk was confirmed as a good source of novel bacteriocinogenic LAB strains, having identified Lactococcus isolates possessing variations in their genomes that suggest the production of a nisin variant not yet described and with potential for use as biopreservatives in food due to its broad spectrum of action.

Highlights

The raw goat milk microbiota is considered a good source of novel bacteriocinogenic lactic acid bacteria (LAB) strains that can be exploited as an alternative for use as biopreservatives in foods
Antimicrobial activity and bacteriocin production Isolates identified as LAB (Gram positive and catalase negative) were subjected to the spot-on-the-lawn method to identify their antimicrobial activity against Listeria monocytogenes ATCC 7644, according to CB Lewus, A Kaiser and TJ Montville [27]
LAB isolates were cultured in MRS broth (Oxoid) at 35°C for 24 h, after which 1 μL aliquots were spotted on the surface of MRS agar (Oxoid) and incubated at 25°C for 24 h under anaerobic conditions (GasPak, BD); brain heart infusion (BHI, Oxoid) broth was added to bacteriological agar at 0.8% (w/v) and L. monocytogenes ATCC 7644 at 105 cfu/mL was overlaid and incubated at 35°C for 24 h

Summary

Introduction

The raw goat milk microbiota is considered a good source of novel bacteriocinogenic lactic acid bacteria (LAB) strains that can be exploited as an alternative for use as biopreservatives in foods. Many studies already demonstrated that BAL has considerable inhibitory activity against pathogenic and Bacteriocins are small peptides that present antimicrobial activity and are of particular interest to food industries, representing natural alternatives to improve the safety and quality of foods [13,15]. Considering these characteristics, new bacteriocinogenic LAB strains and their bacteriocins are continuously searched, only nisin and pediocin are the bacteriocins allowed to be applied in food, including cheeses [15,16]. The differences between these variants are based on the changes in the amino acid chain, what could interfere in their antimicrobial activity

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