Print E-mail
Volume 42, Number 5, October 2009

In vitro combinations of antibiotics and phytochemicals against Pseudomonas aeruginosa

Meena K. Sakharkar, Premkumar Jayaraman, Win Mar Soe, Vincent T. K. Chow, Lim Chu Sing, Kishore R. Sakharkar

Received: September 2, 2008    Revised: October 2, 2008    Accepted: November 5, 2008   


Corresponding author:

Meena K. Satharkar, N3-2C-113B, Nanyang Technological University , Singapore 639798. Email:


Background and purpose: 

Antibiotic combinations are used to enhance antibacterial efficacy and to prevent the development of resistance, In this study, the in vitro activities of antibiotic and phytochemical combinations agains Pseudomonas aeruginosa were tested by the fractional inhibitory concerntration method, derived from the minimal inhibitory concertrations (MICs) of the agends in combination.




The antimicrobial activitiy of phytochemicals, alone and in combination with antibiotics, was evaluated using the checkerboard assay and time-kill curve methods.



There was synergism between gentamicin and caffeic acid, and sulfadiazine and the 3 phytochemicals under investigation (protocatechuic acid, quercetin, caffeic acid). The MIC of sulfadiazine was 256 ug/mL, and of gentamicin was 2 ug/mL. When gentamicin was conbined with one-quarter the MIC of caffeic acid, the MIC of gentamicin was reduced 4-fold. When sulfadiazine was tested with one-quarter the MIC of protocatechuic acid, quercetin, and caffeic acid, the MIC was reduced 4-fold in combination with each of the drugs.



These results indicate the potential efficacy of phytochemicals in combination with antibiotics for enhancing total biological activity.


Key words:

Caffeic acid; Combined modality therapy; Drug resistance; Protocatechuic acid; Quercetin