Hi all,
I have to prepare a stock solution of Sulfamethoxazole for Minimal inhibitory concentration experiments with bacteria. I can't understand very well how I have to dissolve the drug powder. The product information sheet says
"Sulfamethoxazole is very slightly soluble in water, but
is soluble 1 in 50 of alcohol and 1 in 3 of acetone. It is
also soluble in alkali hydroxides. A 10% suspension in
water has a pH of 4 to 6.4". According to what is reported here, I thought to dissolve the powder in ethanol.What I don't understand is if I need to use a dilute ethanol solution or just pure ethanol. And..don't the bacteria die if the antibiotic solution contain alcohol?and what about the amount to weight for a specific volume of ethanol?Does 1 in 50 mean 1 g in 50 ml? If yes, I thought to dissolve 20 mg of powder in 1 ml of solution. Does it make sense?
Thank you very much
Hi Silvia: you are right. It means that you can dissolve 1 g of SMX y 50 mL ethanol, so you can proceed with 20 mg SMX in 1 mL ethanol. Once you get this stock solution you will have to dilute it at least 1/100 in water to get a concentration of 200 mcg SMX/mL. This diluted solution will have only contain 1% ethanol, so no inhibitory effect on bacteria is expected. You will have to prepare more dilutions from this solution for the MICs assay, since the breakdown of resistants is normally below 100 mcg/mL.
Hi Silvia,
You are preparing a 'stock' solution (usually with higher concentration for storage). Later, you have to make a 'working' solution from the stock solution for your experiment (with final concentration suggested by your protocol). At the final concentration level, the ethanol amount should not affect the bacteria, besides overtime the ethanol will evaporate some.
When we grew Agrobacterium, we need to add some antibiotics to make sure that specific plasmids are there. Some of the antibiotics need to be dissolved in ethanol/methanol, then are added to the culture medium. We have not found obvious problems.
The is a difference between solvant and diluant. Firstly, you powder, you can dissolve it in ethanol and after to make dilution, you can use water.
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