Anti-biofilm and anti-quorum sensing properties of orthosiphon stamineus and andrographis paniculata extracts on selected biofilm-producing bacteria

Abstract

Anti-microbial resistance has been escalating and alarming the authorities to find new treatment regimens to quell microbial infections. Alternatively, plants derivatives have been used in common population as supplements for general human health including treatments of certain infections. However, infections due to biofilm-producing microorganisms are daunting in nature, thus researchers have been considering anti-biofilms agents as a new focus. In this study, two potential plants with known antimicrobial properties, namely Orthosiphon stamineus (Misai kucing) and Andrographis paniculata (Hempedu bumi), were investigated to see whether they possess anti-biofilm property. As biofilm formation utilizes quorum sensing (a system of stimuli and response to cell density), anti-quorum sensing activity was checked to determine their mechanisms of action. Plants’ stems and leaves were processed using both ethanol and aqueous (water) as solvents. Different concentrations of extracts (1, 2, and 3 mg/mL) were then challenged against known biofilm-producing bacteria, Pseudomonas aeruginosa and Staphylococcus aureus. Five out of the eight (5/8) extracts showed anti-biofilm effect against biofilm of P. aeruginosa and three of them showed the same effect when tested against S. aureus. The highest percentage of inhibition of P. aeruginosa biofilm (77.84%) was observed in the ethanol extracts of O. stamineus stems and A. paniculata leaves, both at the concentration of 3 mg/mL. Three extracts that showed anti-biofilm effect against S. aureus biofilm were the aqueous extracts of A. paniculata leaves and stems and ethanol extract of O. stamineus leaves. Highest value (19.44%) was recorded by the aqueous extract of A. paniculata stems at the concentration of 3 mg/ml followed by 17.78% at 2 mg/ml concentration. These six extracts were later tested for their anti-quorum sensing activity using a genetically modified Escherichia coli strain, developed by Weiland-Bräuer et al., (2014). None of the extracts showed anti-quorum sensing property. In conclusion, some of the O. stamineus and A. paniculata extracts have anti-biofilm property towards P. aeruginosa and S. aureus, however their mechanism of action has yet to be determined.