Control of Listeria monocytogenes by Bacteriocins Produced by Lactobacillus curvatus MBSa2 during Ripening of Salami

Introduction: Listeria monocytogenes is a ubiquitous pathogen that can survive the technological hurdles usually applied for manufacture of salami. Bacteriocins produced by lactic acid bacteria have a potential technological application in inhibiting the growth of this pathogen. Lactobacillus curvatus MBSa2 is a bacteriocin-producing strain isolated from salami, with anti-Listeria activity in culture medium.

Purpose: The purpose was to evaluate the activity of the partially purified bacteriocin (PPB) produced by the MBSa2 strain on the control of L. monocytogenes in salami, during ripening period.

Methods: PPB was obtained by precipitation with ammonium sulfate followed by SepPak C₁₈ chromatography. Minimal inhibitory concentration (MIC) of PPB was determined by serial dilutions in BHI broth, using L. monocytogenes Scott A as indicator for antimicrobial activity. Samples of salami mixture, prepared with beef meat (10%), pork meat (75%) and lard (15%) and NaCl, spice mix and commercial starter culture T-SPX, were experimentally contaminated with L. monocytogenes Scott A (10⁴-10⁵ CFU/g). The PPB was added to the mixture at the determined MIC value, stuffed into collagen casings and stored for ripening at recommended temperatures. Controls, without added bacteriocin, were also prepared. Listeria counts were performed on days 0, 4, 10, 20, 30.

Results: The MIC value of the PPB against L. monocytogenes was 200 AU/ml. Addition of the PPB resulted in reduction of 0.56 log in the counts of L. monocytogenes immediately after addition of the bacteriocin. After 10, 20 and 30 days, the counts of the pathogen were 1.98, 1.77 and 1.01 log lower than in the salami without added bacteriocin, respectively.

Significance: The PPB of L. curvatus MBSa2 can be used as an additional hurdle for the control of L. monocytogenes in salami.