Evaluation of Antimicrobial Properties and Potential Applications of Pseudomonas gessardii M15 Rhamnolipids towards Multiresistant Staphylococcus aureus

Staphylococcus aureus is a Gram-positive opportunistic human pathogen responsible for severe infections and thousands of deaths annually, mostly due to its multidrug-resistant (MDR) variants. The cell membrane has emerged as a promising new therapeutic target, and lipophilic molecules, such as biosurfactants, are currently being utilized. Herein, we evaluated the antimicrobial activity of a rhamnolipids mixture produced by the Antarctic marine bacterium Pseudomonas gessardii M15. We demonstrated that our mixture has bactericidal activity in the range of 12.5–50 µg/mL against a panel of clinical MDR isolates of S. aureus, and that the mixture eradicated the bacterial population in 30 min at MIC value, and in 5 min after doubling the concentration. We also tested abilities of RLs to interfere with biofilm at different stages and determined that RLs can penetrate biofilm and kill the bacteria at sub-MICs values. The mixture was then used to functionalize a cotton swab to evaluate the prevention of S. aureus proliferation. We showed that by using 8 µg of rhamnolipids per swab, the entire bacterial load is eradicated, and just 0.5 µg is sufficient to reduce the growth by 99.99%. Our results strongly indicate the possibility of using this mixture as an additive for wound dressings for chronic wounds.