Effect of lauric arginate, nisin Z, and a combination against several food-related bacteria

• Lauric arginate (LAE) and nisin Z were evaluated against foodborne bacteria.
• A combination of LAE and nisin Z inhibited foodborne bacteria better than when applied alone.
• SEM and TEM demonstrated leakage of the cytoplasmic membrane and cell lysis following a combination treatment.
• Leakage of phosphate and potassium ions was observed following a combination treatment.
• The potential mode of action of these compounds on bacterial populations is described.

The effects of lauric arginate (LAE) and nisin Z, alone or in combination, on cell damage were investigated against Escherichia coli O157:H7, Listeria monocytogenes and Brochothrix thermosphacta, by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations, efflux of potassium and phosphate ions, and growth inhibition. A combination of LAE with nisin Z caused severe and dramatic changes in the cytoplasmic membrane and cell lysis of both Gram-positive and Gram-negative bacteria. The combination treatment also caused significant potassium and phosphate ion leakage of E. coli O157:H7, L. monocytogenes and B. thermosphacta, when compared with other treatments: 16.62 ± 1.05, 50.35 ± 0.81 and 45.47 ± 1.15 mg/L of potassium ion and 122.66 ± 8.81, 97.96 ± 3.31 and 26.47 ± 13.97 mg/L of phosphate ion after treatment for 6 h, respectively. Bacteria were reduced by approximately 7 log10 CFU/mL within the first hour of treatment and then cells were unable to grow for the remainder of the experiment. Treatment with LAE alone resulted in changes in cellular morphology, coagulation of the cytoplasm, and low level leakage of potassium and phosphate ions in all bacteria tested. Treatment of L. monocytogenes and B. thermosphacta with nisin Z (320 AU/mL of final concentration) resulted in the formation of membrane channels and leakage of potassium and phosphate ions at rather high levels; but the bacteriocin was not effective against E. coli O157:H7. LAE or nisin Z reduced growth of both L. monocytogenes and B. thermosphacta by approximately 7 log10 CFU/mL. Conversely, E. coli O157:H7 was not inhibited by treatments with nisin Z, but decreased by approximately 4.45 log10 CFU/mL after treatment with LAE. These findings provide additional information on the mode of action of these compounds on bacterial populations.