LACTIC ACID BACTERIA ISOLATED FROM RAW MILK AND SOFT CHEESE: DETECTION OF CULTURES ABLE TO PRODUCE BACTERIOCINS AND BACTERIOCIN-LIKE SUBSTANCES AND MOLECULAR IDENTIFICATION

Maria Beatriz Tassinari Ortolani (UFV); Paula Mendonça Moraes (UFV); Kátia Gianni (USP); Abelardo Silva Júnior (UFV); Luís Augusto Nero (UFV)

Lactic acid bacteria (LAB) are being used by food industries due to their ability in producing metabolites, like bacteriocins, with antimicrobial activity against Gram positive pathogens and spoilage microorganisms. The objectives of this study were to identify naturally occurring bacteriocinogenic LAB in raw milk and soft cheese, verifying their sensitivity to proteolytic enzymes, and detecting the presence of nisin codifiers genes in cultures identified as Lactococcus lactis. 389 LAB cultures were isolated from raw milk and soft cheese samples, and submitted to the detection of bacteriocins production against Listeria monocytogenes. 58 (14.9%) LAB cultures were identified as antagonistic, and then submitted to enzymatic tests in order to confirm the proteinaceous nature of antimicrobial substances. Most cultures (44) produced extracts that presented sensitivity to one or more enzymes, confirming their ability to produce bacteriocin-like substances. 20 of these cultures were randomly selected and submitted to genetic sequencing being identified as Lactobacillus plantarum (2) and Lc. lactis subsp. lactis (18). Out of the 18 cultures identified as Lc. lactis subsp. lactis, 7 presented positivity for nisin genes by PCR. The results of the phylogenetic analysis to the identification by genetic sequencing, together with the enzymatic profile of the produced bacteriocins and bacteriocin-like substances, and the positivity of genes variations for nisin codification allow the observation of a great variability among the isolates. This study demonstrated the presence of LAB isolated from raw milk and soft cheese, with the ability to produce nisin and other types of bacteriocins or bacteriocin-like substances, with potential application in foods for the control of L. monocytogenes. For such, further studies are necessary for a better understanding of the antimicrobial potential of these cultures.