Bioautographic TLC assays

Hamburger, M. O. and Cordell, G. A. (1987) A direct bioautographic TLC assay for compounds possessing antibacterial activity J Nat. Prod. SO, 19-22. 

The antibacterial activity of the secoiridoids 14,15, 17-19, 20a, b, 28a and 38, and the caffeoyl esters of phenylethanoid glycosides 22 -27 has also been tested using the direct bioautographic TLC assay as published by Hamburger and Cordell [39]. Bacillus subtilis spp. and Pseudomonas fluorescens were the representatives of the gram-positive and gramnegative bacteria, respectively. The minimum inhibition amount (MIA) was determined. Cefotaxime was used as a positive control. 

In this form of assay, the extract or pure compound is run on a TLC plate, which IS then covered by a medium seeded with the appropriate microorganism. As with direct bioautographic assays, both fungi and bacteria may be investigated. Rahalison et al. (54) have applied this technique for the evaluation of antimicrobial extracts against the yeast Candida albicans and the bacterium Bacillus subtilis. 

The dilution and diffusion methods mentioned above are all well-known classical microbial assays. Only the bioautographic methods are suitable for direct combination of the detection techniques with any kind of chromatographic separation methods. This technique opens up new avenues to detect the effects of samples on microbes after separation of the compounds by opened sorbent-bed (e.g., TLC) chromatography. 

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