I am testing a particular antimicrobial to get its MIC using the microplate assay and the results I get are puzzling. In this specific case I have 8 replicates for each concentration but the MIC is never sharp for this antimicrobial.
at 0.125% I see inhibition in 1 well
at 0.25% I see inhibition in 2 wells
at 0.5% inhibition in 4 wells
at 1% inhibition in 7 wells
The antimicrobial is cidal. I have never seen such a behavior. What do you guys think is happening?
Dear Zarina
I think it is a normal result at which as you reported with the increase the test concentration, the rate of inhibition will increase. as you know MIC is the lowest concentration of antimicrobial agent which inhibits bacterial growth after overnight incubation. To know the cidal concentration of antibiotics, you need to culture the inhibited growth suspension into the agar plates. After the overnight incubation, the plate which shows no colonies on plate will represent cidal concentration and we will refers to this antimicrobial agent as bactericidal agent.
Best and kind regard
An explanation could be that, the antimicrobial sustance is mot well homogeneized during the experiment: Also, the antimicrobial substance should be properly mixed with microbial agent (a shaker is usualy used in this test)
Dear Zarina
I think it is a normal result at which as you reported with the increase the test concentration, the rate of inhibition will increase. as you know MIC is the lowest concentration of antimicrobial agent which inhibits bacterial growth after overnight incubation. To know the cidal concentration of antibiotics, you need to culture the inhibited growth suspension into the agar plates. After the overnight incubation, the plate which shows no colonies on plate will represent cidal concentration and we will refers to this antimicrobial agent as bactericidal agent.
Best and kind regard
F. Romain Fouelefack , I think you are right. There could be a problem with homoginity of the solution. Mushtak T. S. Al-Ouqaili: Usually I get I very sharp number. Let's say, at 0.5% I see inhibition of growth in all the replicates. This "behaviour" where I see inconsistency among the replicates is quite unusual.
Better you perform disc diffusion assay by all these concentrations. I think picture will be very clear.
If you test any plant material which contain many phytochemicals together, this type of result may be considered as normal. With dilution, some phytochemicals may loss activity more than others.
But for single component, dilution of the test material, the diluent, sensitivity of the testing bacteria to the component etc. factor play the main roles.
Agree with @ https://www.researchgate.net/profile/Mushtak_Al-Ouqaili
regards
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