A new method for concomitant evaluation of drug combinations for their antimicrobial properties

Microbial pathogens have developed resistance mechanisms to almost every antibiotic available. There is a need to synthesize or screen new natural compounds to combat the development of drug-resistant pathogens. One of the commonly used methods to evaluate the antimicrobial activity of two or more antibiotics involves a checkerboard assay, which is cumbersome, time-consuming, and expensive. We have developed a quick, reliable, and cost-effective method to evaluate the antimicrobial effect of two or more antibiotics at fixed doses with different concentrations of a novel natural ingredient or test compound. The technique involves the following steps:•Preparation of a bacterial culture of the test strain at 0.5 McFarland standard (0.1 OD at 600 nm), and preparation of stock solutions for the chemical of interest and standard drugs.•The required amount of all three components can be dispensed into respective wells of a microplate using multichannel pipette.•Optical density (OD) values obtained would be directly related to the individual as well as combined effect of compounds on the given bacterial strain.