Antimicrobial activity and optimisation of aureobasidin A production by Aureobasidium pullulans PA-2 against Escherichia coli and Staphylococcus aureus

This work aims to separate the antimicrobial lipopeptides from fermentation by Aureobasidium pullulans PA-2, and to verify its antimicrobial activity and the optimum conditions of the lipopeptide production. Using a high-performance liquid chromatography analysis, the lipopeptides with antimicrobial activity were evaluated with the agar well diffusion test. Response surface methodology was used to determine the optimum conditions for lipopeptides from A. pullulans PA-2. The lipopeptides with antimicrobial activity in the fermentation supernatant of the PA-2 strain was found to be aureobasidin A (AbA). The in vitro antagonistic tests showed that the minimal inhibitory concentration of AbA against Staphylococcus aureus and Escherichia coli was 0.5 and 1.0 mg/mL, respectively. The optimal fermentation conditions were an inoculum size of 6.8% (v/v) (OD600 = 0.25), a rotation speed of 216 rpm, a culture temperature of 26 degrees C, a liquid volume of 125 mL and an initial pH of 7. Under these conditions, the predicted yield of the antimicrobial lipopeptides by the model was 940 mg/L, the observed yield was 920 mg/L, which was 51% more than that before the optimisation (610 mg/L).