Hello
I want to do MIC test for staphylococcus aureus with Nisin A. I have a stock of Nisin with 68%potency. I prepared 1mg/ml concentration of nisin in deionized water. then make serial dilution in 96 well plate. In all of concentration ureos was grew. My negative control was grew too. Can you help me about it?
Dear Roghayeh Mokhtari Asl,
There are some point and question in your procedure.
1.The best solvent for nisin is hydrochloric acid 0.01M, because it has the maximum pH stability at this solution. What was the pH of the deionized water? Also use the hydrochloric acid 0.01M as negative control.
2.What was storage conditions of stock nisin? Room temperature or refrigerator?
3.Bacterial strains have different sensitivity to nisin. You must use suitable concentration of nisin in your experiments.
4.What was inoculum size? How much you add staphylococcus aureus culture to each well? Colony count standardization or specific OD600nm?
5.What was incubation temperature?
6.Do you evaluate adsorption study (surface absorption of nisin to wells) for 96 well plates?
7.I recommend, at first you standard the stock nisin with a well known and commercial nisin such as sigma and then use U/mL biological activity of nisin instead of mg/mL.
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