Rhamnolipids on Aedes aegypti larvae: a potential weapon against resistance selection.

The resistance of Aedes aegypti to chemical insecticides has been reported and our work proposes the use of biosurfactants as an alternative larvicide. We evaluated the effect of rhamnolipids against larvae of pyrethroid-resistant and susceptible A. aegypti strains. Time-mortality and sublethal effects were evaluated via survival analysis and swimming behavior, respectively. Rhamnolipids showed larvicidal effect at all tested concentrations. Rhamnolipids at 300 mg L-1 killed 100% of both susceptible and resistant larvae within 24 h of exposure and 99% after 30-days stored (pyrethroid-susceptible larvae). Regarding the sublethal effects, the swimming rate was reduced in 50 and 100 mg L-1 of rhamnolipids in grouped (pyrethroid-susceptible) larvae. Rhamnolipids at 50 mg L-1 reduced the distance and speed and increased the number of stops and resting time of individualized pyrethroid-susceptible larvae. The larvicidal effect of the rhamnolipids evaluated demonstrates that these compounds represent an alternative to control A. aegypti.

Bacillus subtilis TR47II as a source of bioactive lipopeptides against Gram-negative pathogens causing nosocomial infections.

This study aimed to investigate the antimicrobial, antibiofilm, and cytotoxic effects of biosurfactant lipopeptides synthesized by Bacillus subtilis TR47II. For this purpose, the lipopeptides were partially purified using a three-step process and characterized. In the first step, the crude extract obtained from acid precipitation exhibited strong antibacterial activity against the Gram-negative opportunistic pathogens Alcaligenes faecalis ATCC 8750, Achromobacter xylosoxidans ATCC 13138, Pseudomonas alcaligenes ATCC 14909, and Pseudomonas putida ATCC 15175. Moreover, partial inhibition was observed against Klebsiella aerogenes ATCC 13048 (42%), Escherichia coli ATCC 25922 (16%), and Pseudomonas aeruginosa ATCC 27853 (47%). The lipopeptides in the crude extract were extracted with methanol and fractioned on a silica gel chromatography column, rendering four TLC-pooled chromatographic fractions, named F1, F2, F3, and F4. The chromatographic fraction F4 was the most bioactive, with MIC values between 300 and 600 µg mL-1. Besides, F4 at sub-MIC doses dislodged the biofilms of A. faecalis, A. xylosoxidans, and P. alcaligenes by about 100, 85, and 81%, respectively. No cytotoxic effect was observed in mammalian cells at MIC. MALDI-TOF-MS analysis revealed that F4 contained cyclic lipopeptides belonging to two families: iturins (m/z 1004 to 1087) and fengycins (m/z 1424 to 1545). The dual effect of F4 on planktonic and sessile growth could suggest that the synergistic application of these biosurfactants could be efficient in the control of these opportunistic pathogens.