Anti-biofilm and Anti-quorum Sensing Activities of the Red Seaweed, Gracilaria changii and its Associated Bacteria

Antimicrobial resistance (AMR) is one of the biggest threats to global health and new therapeutic strategies with the potential to reduce AMR are urgently required. Biofilm formation provides advantages for pathogenic bacteria to protect themselves from antibiotics due to the low penetration of antibiotics into the biofilm. Seaweeds have been found to have a variety of bioactive compounds that prevent the attachment and inhibit the biofilm formation by pathogenic bacteria. This study assessed the anti-biofilm and anti-quorum sensing (AQS) activities from the red seaweed, Gracilaria changii, and its associated bacteria. Crude methanol extract of G. changii at 0.01- and 0.001 mg mL −1 resulted in a decrease in Vibrio campbelli BB120 biofilm formation. The crude extract of G. changii inhibited quorum sensing (QS) activity of the reporter strain Chromobacterium violaceum CV026 through inhibition of the purple violacein pigment production using disc diffusion assay. Thin-layer chromatography (TLC) overlay assay was performed to screen for the potential AQS metabolites from G. changii . Out of the six separated compounds, three compounds with the R f values of 0.94, 0.57 and 0.28 showed QS inhibition zones. A bacterium isolated from the seaweed, Halomonas sp. promoted the bud formation of the seaweed and produce the highest amount of indole-3-acetic acid (IAA) compared to the other bacterial isolates This study shows that G. changii extract has anti-biofilm and AQS activities which could be a potential biocontrol agent. Furthermore, the symbiotic relationship between the Halomonas sp. and G. changii could also be used as growth promoting factor in seaweed cultivation.