Evaluation of Anti-quorum Sensing Potential of Saraca asoca (Family Caesalpiniaceae) against Chromobacterium violaceum and Pseudomonas aeruginosa PA01

Aim: The present study was performed to evaluate the anti-quorum sensing (QS) potential of traditional medicinal herb Saracaasoca (family Caesalpiniaceae) stem bark extract against Chromobacterium violaceum and Pseudomonas aeruginosa PA01.

Study Design: First, the test sample (bark extract) was screened for anti-QS activity. Then systematic in-vitro and biochemical tests were performed to evaluate the effect of the test sample on the QS mediated virulence factors.

Place and Duration of Study: All the experimental works were performed in Lab 311, pharmacology division, CSIR-NBRI Lucknow from June 2019 to October 2019.

Methodology: The samples of Saraca asoca stem bark were washed, dried and extracted using 70% methanol. The minimum inhibitory concentration (MIC) of the prepared Sarca asoca bark extract was determined using the Alamar blue assay, and the anti-QS activity was screened using standard agar overlay method against CV 12472 at subinhibitory concentrations 100, 200 and 300 µg (< MIC value). SAE effect on biofilms formation was assessed by growing biofilms on glass slides in a static culture of PA01. Anti-virulence effect of SAE on the production of QS-regulated virulence factors such as Pyocyanin, proteases, elastases, rhamnolipid and alginate in Pseudomonas aeruginosa was determined using the supernatant of a 24 hours old broth culture of PA01 supplemented with SAE. Using the agar plate technique, the swimming and swarming motility assays were conducted on 0.3% and 0.5% agar plates respectively. One-way ANOVA was used to analyze the data, presented as mean ± SD (standard deviation) of three independent experiments.

Results: Preliminary screening results showed significant QS inhibition against CV 12472 in an agar overlay disk diffusion assay in a concentration-dependent manner. Data from the biofilm assay showed loose, distorted, irregular PA01 biofilm formation at 200 µg (48%) and 300 µg (65%). SAE caused a significant drop in virulence factor production, with maximum reduction in pyocyanin (58%), proteases (67%), elastases (52%), rhamnolipid (53%), and alginate (44%) observed at 300 µg concentration. At SAE sub-lethal concentrations (200 and 300 µg), both the swimming and swarming motility of PA01 were significantly inhibited.

Conclusions: The present study demonstrates the broad-spectrum anti-QS potential of SAE, reported for the first time, suggesting that SAE could be considered as an alternative herbal source to develop antimicrobial agents which can be either solitary or synergistically with conventional antimicrobial drugs.