GIIs= ZDI in combination / total of ZDIs of the two agents in single action in order to corroborate the synergistic activity of the antibiotic in combination with the plant extracts, and synergy between the plants extracts. The synergistic, additive and antagonistic activities, if any, in between any two of the antimicrobial agents were defined with GIIs > 0.5, 0.5 and < 0.5.
Article Synergistic anti– Staphylococcus aureus activity of amoxicil...
All my results are above 0.5 but they are not synergistic.
E.g. Ciprofloxacin = 32 mm (zone of inhibition)
Plant extract = 2 mm (zone of inhibition)
Cipro + plant extract combined disk = 30 mm (zone of inhibition)
Should I take the synergy index as 1 instead of 0.5?
I see that you are doing it the way the article you cited does, so the method should be correct. In the example you give:
GII = 30 / (32+2) = 0.88
I understand your concern, as it is > 0.5, it should be classified as a synergistic effect when clearly does not match this definition.
If we strictly consider synergy, additivity and antagonistic as in the article, synergy would be a value over 1, additivity would be exactly 1 and antagonistic effect would be any value below 1.
I have never calculated synergy by measuring inhibition zones, I have always done it in liquid assays, so the way I did it surely differs (I have calculated FICI, fractional inhibitory concentration index).
I would recommend you look for another article in order to support the use of this formula.
Jesús Perales-Adán
Dear Jesús Perales-Adán
I remain very thankful for your answer.
We still haven't tested FICI. I too think that is more accurate. Only three articles available online mention about the GII index for calculating the synergy index & they too use the exact same formula. For the time being I shall take the synergy value as >1.
Dear Mac Dz , I would recommend you do so.
If you finally manage to do the checkerboard assay to determine the synergy through FICI, feel free to ask me any question.
- Badges
- Science topic
- Similar topics
- Biological Science
- Botany
- Pharmaceutical Botany
- Plant Extracts