The main focus is on plants that have traditionally been used to treat ailments of a bacterial or fungal origin. Four complementary assays are carried out against the human pathogens S. aureus, P. aeruginosa, E. coli and C. albicans.

1. disc diffusion assay

• small paper disc impregnated with the test compound
• placed on an agar plate inoculated with microbes
• test compound diffuses through the agar which gives a concentration gradient in the agar
• if inhibitory concentrations are reached, there will be no growth of the microbes, which can be seen as a clear zone around the disc

2. broth dilution assay

• microbes incubated with different concentrations of test compounds
• growth can be seen visibly or by measuring the turbidity
• plating the solutions out on agar plates, counting colonies after incubation (distinguish between microbiostatic and microbicidal)

3. Resazurin assay

• based on the reduction of blue Resazurin to pink Resorufin
• reduction by microbial dehydrogenase enzymes
• colour change is visible, absorbance can be measured at 505 nm

active compounds

non-active compounds

4. Fluorescein Diacetate assay

• based  on the hydrolysis of colourless fluorescein diacetate (FDA) into yellow-green fluorescein

• hydrolysis by non-specific esterases found in healthy, growing microbes

• fluorescence measured at 405 nm excitation and 520 nm emission

• microbes incubated with the test compounds overnight, FDA added and fluorescence measured

      active       non-active