In vitro antibiofilm activity of tormentic acid against Pseudomonas aeruginosa

Abstract Background : Biofilm formation is the cause for the prevalence of nosocomial infections. Pseudomonas aeruginosa is one of the leading cause of nosocomial infections and affects more than 2 million patients. Infections caused by P. aeruginosa can be very serious and life-threatening. P. aeruginosa can adhere to biotic and abiotic surfaces through the organisation of bacterial biofilms known to confer drug resistance. Consequently, the logical and strategic intervention against bacterial biofilms is the use of multi-targeted combinational therapies. The present study reports the antibacterial and antibiofilm effect of tormentic acid and Callistemon citrinus extracts on P. aeruginosa . Methods : Tormentic acid, hydroethanolic extract, and DCM: methanol extract from C. citrinus were studied for their inhibitory effects on the growth of P. aeruginosa using the microbroth dilution method. Their effect on biofilms was studied using a crystal violet. Results : These compounds did not effectively inhibit growth because the minimum inhibitory concentration (MIC) was greater than 100 µg/ml. The standard drug, ciprofloxacin inhibited growth with an MIC of 0.25 µg/ml. Ciprofloxacin had a minimum biofilm inhibitory concentration (MBIC) greater than 1 µg/ml. Tormentic acid and the two extracts were able to significantly inhibit the adhesion of P. aeruginosa cells, which led to an indirect reduction of biofilms formed at 100 µg/ml. The result of the biofilm detachment assay showed that tormentic acid and DCM: methanol extract had a significant effect on biofilm disruption while the hydroethanolic extract had no effect on biofilm detachment. Capsular polysaccharide analysis showed that the test samples tormentic acid, hydroethanolic, and DCM: methanol extracts significantly reduced the amount of capsular polysaccharide content at 100 µg/ml. Ciprofloxacin at 0.25 µg/ml (MIC) did not reduce the amount of extracellular polysaccharide formed. Conclusions : Tormentic acid and extracts significantly reduced amount of extracellular polysaccharide content, which are an important requirement in cell adhesion process resulting in reduced amount of biofilms formed. Tormentic acid can be considered as a candidate compound for the development of antibiofilm drugs.