I have an extract that is more effective at lower concentrations against tested strains of bacteria. I have done some research and some says it might be to do thickness of the extract that doesn't allow it to diffuse into the plate equally. but to the naked eye it doest seem that way.
Any suggestions would be greatly appreciate it.
Substantive activity of an extract at lower concentration may be a consequence of the menstruum used. Water at a higher temperature can yield more than ethanol. Also dried leave may also show more antimicrobial effect than wet leave whose moisture may be a media for the growth of microorganisms....
The Eagle effect describes a phenomenon in which bacteria or fungi exposed to concentrations of antibiotic higher than an optimal bactericidal concentration (OBC) have paradoxically improved levels of survival than at the OBC due to a decreased net rate of cell death.
It was just a click away on google. Anyways I am sharing the relevant link
Article The Eagle Effect and Antibiotic-Induced Persistence: Two Sid...
This one is original finding
Eagle, H. (1948). A paradoxical zone phenomenon in the bactericidal action of penicillin in vitro. Science 107, 44–45. doi: 10.1126/science.107.2767.44
You may also consider precipitation/crashing of compound at higher concentration also.....which will make it unavailable to cells, if that is case.
Hope that helps!
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