Effect of MA01 rhamnolipid on cell viability and expression of quorum-sensing (QS) genes involved in biofilm formation by methicillin-resistant Staphylococcus aureus

A group of biosurfactants, called rhamnolipids, have been shown to have antibacterial and antibiofilm activity against multidrug-resistant bacteria. Here, we examined the effect of rhamnolipid biosurfactants extracted from Pseudomonas aeruginosa MA01 on cell growth/viability, biofilm formation, and membrane permeability of methicillin-resistant Staphylococcus aureus (MRSA) ATCC6538 bacterial cells. The results obtained from flow cytometry analysis showed that by increasing the concentration of rhamnolipid from 30 to 120 mg/mL, the cell viability decreased by about 70%, and the cell membrane permeability increased by approximately 20%. In fact, increasing rhamnolipid concentration was directly related to cell membrane permeability and inversely related to cell survival. Microtiter plate biofilm assay and laser scanning confocal microscopy analysis revealed that rhamnolipid, at a concentration of 60 mg/mL, exerts a reducing effect on the biofilm formation of Staphylococcus aureus. Real-time PCR analysis for monitoring the relative changes in the expression of agrA, agrC, icaA, and icaD genes involved in biofilm formation and related to the quorum-sensing pathway after treatment with rhamnolipid indicated a reduced expression level of these genes, as well as sortase A gene. The results of the present study deepen our knowledge regarding the use of microbial natural products as promising candidates for therapeutic applications.

Automated summary

The study demonstrates that rhamnolipid biosurfactants extracted from Pseudomonas aeruginosa have good antibacterial and antibiofilm activity against MRSA ATCC6538 bacterial cells, making them promising candidates for therapeutic applications.