The activity of bacteriocins from Carnobacterium maltaromaticum UAL307 against gram-negative bacteria in combination with EDTA treatment

Bacteriocins from gram-positive bacteria are potent antimicrobial peptides that inhibit pathogenic and food-spoilage bacteria. They are usually ineffective against gram-negative bacteria because they cannot penetrate the outer membrane (OM). Disruption of the OM of some gram-negative bacteria was reported to sensitize them to certain bacteriocins. This study evaluates the activity of three purified bacteriocins [carnocyclin A (CclA), carnobacteriocin BM1 (CbnBM1) and piscicolin 126 (PisA)] produced by Carnobacterium maltaromaticum UAL307, which has been approved for preservation of food in United States and Canada, against three gram-negative bacteria (Escherichia coli DH5α, Pseudomonas aeruginosa ATCC 14207 and Salmonella Typhimurium ATCC 23564). Their efficacy is compared with bacteriocins of other classes: the lantibiotics nisin A (positive control) and gallidermin, and the cyclic peptide subtilosin A (SubA). In combination with EDTA, CclA inhibited both E. coli and Pseudomonas. PisA inhibited Pseudomonas, but CbnBM1 showed weak activity toward Pseudomonas. In comparison, nisin and gallidermin inhibited the growth of all three strains, whereas SubA was active against E. coli and Pseudomonas only at high concentrations. The results reveal that UAL307 bacteriocins can inhibit gram-negative bacteria if the OM is weakened, and that the different classes of bacteriocins in this study exert unique modes of action toward such bacteria.