Aims: Marine bacteria have been reported to produce potential natural pigment with pharmaceutical properties and their growth can be manipulated in the laboratory to increase pigment production and their antimicrobial activity. Hence, this study aimed to enhance the prodigiosin production in Serratia marcescens IBRL USM84 by improving physical conditions. Methodology and results: The quantification of the pigment produced by S. marcescens IBRL USM84, bacterial cell growth, and its antibacterial activity in the broth medium were determined using a spectrophotometry method. Meanwhile, the antibacterial effect of red pigment on MRSA cells was observed under a scanning electron microscope (SEM). This marine isolate produced the highest yield of prodigiosin (6.95 μg/mL) when cultivated in marine broth with the addition of 0.2% of agar, 25 °C incubation temperature, initial medium pH of 7, 150 rpm of agitation speed for 48 h of cultivation time under light illumination. There was an increment of 151.81% in prodigiosin production after enhancement compared to before the enhancement of cultural conditions. SEM observations revealed that severe damage to the cell’s morphologies was exposed to red pigment as indicated by the formation of small dents, which led to completely collapse and eventually, cell death. Conclusion, significance and impact of study A positive correlation between pigment production and antibacterial activity was observed in the present study. The results supported the fact that marine bacteria are a reservoir of various pigments with antimicrobial properties. Also, the pigment production by S. marcescens and its antibacterial activity were significantly influenced by physical parameters.
Prodigiosin ; Serratia marcescens ; Marine Biology

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.

Eleusine ; Pseudomonas aeruginosa ; Quorum Sensing ; Serratia marcescens ; Prodigiosin