Enhanced Control of Listeria monocytogenes by Combining High Hydrostatic Pressure (HHP) and Nisin: Impact of Strain Tolerance, Pressure Level, Nisin Concentration and Medium

Abstract Listeria monocytogenes is a major foodborne pathogen capable of surviving under adverse conditions, and combining high hydrostatic pressure (HHP) with nisin offers a promising strategy for its effective control. However, knowledge remains limited regarding their combined efficacy across strains with different pressure tolerances and in varied model systems. This study systematically assessed the antimicrobial efficacy and synergistic effect of HHP (200-350 MPa, 10 min) combined with nisin (100–500 IU/mL) against five L. monocytogenes strains with varying pressure tolerance in BHI broth and ACES buffer. Nisin MICs ranged from 300 to 500 IU/mL, with 10430S being the most susceptible. Combined HHP-nisin treatments resulted in a significant synergistic effect across most tested conditions. At 300 MPa + 500 IU/mL nisin, combined inactivation reached 5.2-5.3 log 10 reduction in BHI and 2.7-4.0 log 10 in ACES for the most sensitive strains (LO28, FBR13, 10403S). The synergistic effect was mostly observed at higher pressures (300-350 MPa) and nisin concentrations (500 IU/mL), reaching up to 2.9 log 10 reduction in ACES buffer and 1.5 log 10 reduction in BHI. The antimicrobial efficacy and synergistic effect were strongly influenced by strain, pressure intensity, and medium. The highest synergistic effect was observed in FBR13 under most conditions ( p < 0.05) despite not being the most pressure-sensitive strain. In BHI, synergism was generally lower than in ACES buffer across most treatment conditions, except at 500 IU/mL. At 300 MPa + 200 IU/mL nisin, the synergistic effect ranged from 0.6 to 1.2 log 10 reduction in ACES and 0.1 to 0.6 log 10 in BHI. Nisin alone resulted in significantly greater reduction in ACES (1.1 to 1.9 log 10 reduction) than in BHI (0.3 to 1.1 log 10 reduction) across all concentrations. This study highlights the strong potential of the HHP-nisin combination as a multi-hurdle approach for L. monocytogenes control, offering valuable insights to optimize treatment parameters.