Bioautography
The procedure in bioautographic methods is similar to the one
used in agar diffusion methods. The difference is that the tested
compounds diffuse to inoculated agar medium from the chromatographic
layer, which is adsorbent or paper [20,21]. In the contact
bioautography, the TLC plate or paper chromatograms are placed
on the inoculated agar surface for some minutes or hours to allow
diffusion. Next, the plate is removed and the agar layer is incubated.
The zones of inhibition growth appear in the places, where
the antimicrobial compounds were in contact with the agar layer.
In the immersion (agar-overlay) bioautography, the plate is first
immersed in or cover with agar medium, which after solidification
is seeded with the tested microorganisms and then incubated
[22–24]. In order to enable better diffusion of the tested compound
into the agar surface, the plates can stay at low temperature
for a few hours before incubation. This method is a combination
of contact and direct bioautography, because the antimicrobial
compounds are transferred from the chromatogram to the agar
medium, as in a contact method, but the agar layer remains onto
the chromatogram surface during the incubation and visualization,
as in direct bioautography