Search

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Three Bacillus strains isolated from honey samples and bee gut were pre-selected for their in vitro antimicrobial activity against Paenibacillus larvae and Ascosphaera apis, important honeybee pathogens. The analysis of their 16S rRNA sequences revealed that C4, M1 and G2III strains belong to the subtilis species. Surfactin synthesis was verified by IR spectroscopy and HPLC studies. Surfactin inhibited P. larvae but it failed to affect A. apis. Vegetative cells of P. larvae were affected as soon as they came in contact with the surfactin sample; two orders of magnitude less in log scale were recorded. Optimal surfactin production was observed in MEL medium, a broth with molasses as the only carbon source. Bacillus subtilis G2III strain exhibited the highest levels of surfactin synthesis in BHI and MEL broths: 1391AU/ml and 2782AU/ml, respectively. Since only A. apis inhibition was observed when cell suspensions were assayed, we suspect that there may be an antimycotic compound within cells. The co-production of surfactin and a fungicide by these strains might biologically control bee pathogens in apiculture. [Copyright &y& Elsevier]