As I need to check the effect of an antimicrobial agent against E.coli. So I will perform the minimal inhibitory concentration test, for which If I will take 2 ml of antimicrobial solution (15 mmol) and I will add a loop full of bacterial culture (10 µl) of 10^5 CFU/ml, does it change the concentration of any of them? Because apparently when we add liquid culture to antimicrobial solution it might be diluted. So is there any change happened or it will be considered same as before i.e. 15 mmol and 10^5 CFU/ml?
Thank you
Inoculum effects are often seen in MIC assays for antibiotics. That is why the assays are standardized on a certain inoculum size. The inoculum refers to the concentration of bacteria (CFU/mL), which is usually estimated based on the turbidity of the culture (McFarland units)
The amount of dilution of 2 ml by 10 µl is negligible, as far as the antibiotic concentration is concerned. However, using a loop-full of bacteria is rather approximate. It would be better to use a pipettor to add a specific volume of the culture, and to be consistent about the optical density of the culture between experiments.
Hina Saif Hi, the change will be negligible in your case. However, if you want to avoid it, calculate and take the conc. of the antibacterial agent that is appropriate with 2.01 mL of the total sample. Add that concentration in 2 mL and then when you add the extra 10 uL later, the conc. of the agent will be 15 mM.
Bacterial inoculum changes the antibacterial solution strength, One needs to standardize the inoculum to have the same number of cells.
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