LAUSR

Carnobacterium maltaromaticum and Carnobacterium divergens are often predominant in the microbiota of vacuum-packaged (VP) meats after prolonged storage at chiller temperatures, more so in recent studies. We investigated the antibacterial activities of C. maltaromaticum and C. divergens (n=31) from VP meats by phenotypic characterization and genomic analysis. Five strains showed antibacterial activities against Gram-positive bacteria in spot-lawn assay, with C. maltaromaticum strains having an intergeneric and C. divergens strains an intragenic inhibition spectrum. This inhibitory activity is correlated with production of predicted bacteriocins including carnobacteriocin B2 and carnolysin for C. maltaromaticum, and divergicin A for C. divergens, respectively. The supernatants of both species cultured in Meat Juice Medium under anaerobic conditions retarded the growth of most Gram-positive and -negative bacteria in broth assay in a strain-dependent manner. C. maltaromaticum and C. divergens produced formate and acetate but not lactate under VP meat relevant conditions. The relative inhibitory activity by Carnobacterium strains was significantly correlated (P <0.05) to the production of both acids. Genomic analysis revealed the presence of genes in both species required for respiration. In addition, two clusters of C. divergens have the average nucleotide identity below the cut-off value for species delineation and thus should be considered to be two sub-species. In conclusion, both bacteriocins and organic acids are factors contributing significantly to the antibacterial activity of C. maltaromaticum and C. divergens in VP meat relevant conditions. A few Carnobacterium strains can be explored as protective cultures to extend the shelf-life and improve the safety of VP meats.Importance: The results of this study demonstrated that both bacteriocins and organic acids are important factors contributing to the antibacterial activities Carnobacterium from VP meats. This study demonstrated that formate and acetate are the key organic acids produced by Carnobacterium and their association with the inhibitory activity of carnobacteria under VP meat relevant storage conditions. The role of lactate, on the other hand, may not be as important as previously believed in the antimicrobial activities of Carnobacterium spp. on chilled VP meats. These findings advance our understanding of the physiology of Carnobacterium, to better explore their biopreservative properties for chilled VP meats.