Why is the Stock solution for preparing final concentration of crude extract two fold above MIC (for determination of antagonistic reaction) and 4 times below MIC in Muller-Hinton agar during synergistic study with antibiotics?
I read did in an article but couldn't understand why it's so
Novel Synergistic Activity of Quercus infectoria Gall Extract with Ceftazidime Against Standard and Multiple Drug Resistant Pseudomonas aeruginosa and Escherichia coli Isolates
Elham Isaei, MD1; Shahla Mansouri, PhD2,3*; Maryam Rahmani, MD4; Fariba Sharififar, PhD5; Atefeh Salary, MD1
As to Why? - the wanted to see the effect on antibiotic efficacy of adding extracts. For synergism - they used an ineffective level (< MIC) of extract with various concentrations of the antibiotic to see if the combination MIC was less than the only antibiotic MIC. They did show increased efficacy of the combination so concluded synergism.
For antagonism - they added higher levels of extract with antibiotic at MIC to see it required more antibiotic to inhibit. It's hard to follow here - but I think they concluded the effect was indifferent.
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