Inhibitory Activity of Surfactin, Produced by Different Bacillus subtilis Subsp. subtilis Strains, Against Listeria Monocytogenes Sensitive and Bacteriocin-Resistant Strains

Three surfactin-producing Bacillus subtilis strains, C4, M1 and G2III, previously isolated from honey and intestines from the Apis mellifera L. bee, were phylogenetically characterized at sub-species level as B. subtilis subsp. subtilis using gyrA gene sequencing. 

The antagonistic effect of surfactin was studied against seven different Listeria monocytogenes strains, 6 of which were resistant to bacteriocins. Surfactin showed anti-Listeria activity against all 7 strains and a dose of 0.125mg/mL of surfactin was enough to inhibit this pathogen. Surfactin sintetized by B. subtilis subsp. subtilis C4 inhibited the pathogen in lower concentrations, 0.125mg/mL, followed by G2III and M1 with 0.25 and 1mg/mL, respectively. In particular, a dose of 0.125mg/mL reduced the viability of L. monocytogenes 99/287 RB6, a bacteriocin-resistant strain, to 5 log orders. Surfactin assayed maintained anti-Listeria activity within a pH range of between 2 and 10, after heat treatment (boiling for 10min and autoclaving at 121°C for 15min) and after treatment with proteolytic enzymes. 

These results suggest that surfactin can be used as a new tool for prevention and the control of L. monocytogenes in different environments, for example, in the food industry.