Introduction: Nosocomial contaminants such as Pseudomonas aeruginosa and Serratia marcescens are increasingly developing resistance to many antibiotics. One of the promising alternatives that may complement, if not substitute, the use of antibiotics is quorum quenching, the process of interfering with chemical signals that mediate communication between microorganisms. Eleusine indica, a ubiquitous grass used traditionally to treat infections, has been shown to contain metabolites, such as fatty acid derivatives and p-coumaric acid, capable of quorum quenching. To date, there has been no study on the quorum quenching activity of E. indica.

Objectives: This study aimed to determine the in vitro activity of crude ethanolic extract of E. indica leaves against selected quorum-sensing regulated virulence factors of P. aeruginosa and S. marcescens.

Methodology: E. indica leaves were collected, washed, air-dried, and homogenized. Following ethanolic extraction and rotary evaporation, the extract was screened for antimicrobial activity through disk diffusion test and broth microdilution assay. The quorum quenching activity of the extract against P. aeruginosa was measured through swarming motility assay, while the activity against S. marcescens was measured through swarming motility and pigment inhibition assays. The quorum quenching assays were conducted in triplicates, and analysis of variance (ANOVA) was performed to identify differences among the treatment groups.

Results: Disk diffusion test revealed that no zones of inhibition formed against both P. aeruginosa and S. marcescens for varying concentrations of up to 200 mg/mL of the crude extract. Likewise, the MIC of the extract against both P. aeruginosa and S. marcescens was determined to be >200 mg/mL. However, it was shown that the extract, at 50 mg/mL, has statistically significant activity (p<0.05) against the swarming motility of P. aeruginosa, and it is 71.6% as effective in reducing the swarming area of the bacteria compared to cinnamaldehyde. This was not observed when the extract was tested against the swarming motility of and pigment production by S. marcescens.

Conclusion: In this study, the quorum quenching activity of the crude ethanolic extract of E. indica leaves was found to be effective against P. aeruginosa but not against S. marcescens. The compounds that will be identified by further studies may conceivably be used as an adjunct therapy in P. aeruginosa infections and as coating agents in medical devices.