Impact of Nisin on Growth Inhibition and Biofilm Formation Capacity of Listeria monocytogenes

The effects of nisin on growth inhibition and biofilm formation were studied in two Listeria monocytogenes strains, LM_ATCC 19115 and LM_18, at concentrations ranging from 14 to 450 µg/mL. The maximum rate of OD600 increase (μmax) showed no significant concentration-dependent change in LM_ATCC 19115, whereas LM_18 exhibited a downward trend. Maximum OD600 dropped progressively and significantly at 225 and 450 µg/mL in both strains. Although concentrations of 14–56 µg/mL supported gradual growth that paralleled the control, the highest nisin concentrations significantly prolonged the lag phase of both strains and eventually decreased biomass by 64% and 51% for LM_ATCC 19115 and LM_18, respectively. Consequently, nisin reduced biofilm formation, with no biofilm observed for LM_ATCC 19115 at 450 µg/mL. However, both strains retained biofilm-forming capacity at 14–113 µg/mL concentrations. In LM_ATCC 19115, biofilm formation decreased independently of growth, along with significantly increased expression of the motility gene flaA and quorum sensing regulator agrA. In contrast, for LM_18, biofilm reduction corresponded to growth inhibition, with significant downregulation of the virulence gene hly. The observed strain-specific patterns of growth and biofilm formation warrant further investigation with a broader range of strains to better define and address the limitations of nisin application.