I made some blood agar plates with TSA+5% blood. They turn into chocolate color after 48hr in 37℃, but the commercial one doesn't. How can I make the same stable blood agar plate?
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I use fresh human blood. Both Agar and blood were incubate in 55℃ water bath then put together. The result were cherry red agar plate. No problem under room temperature, just turn darker and darker in 37℃ incubator.
Usually the blood agar base contain peptone ,Tryptose ,Sodium chloride and Agar.Final pH is usually adjusted around 7.Then you cool the autoclaved blood agar base upto about 45 C temperature and then use the medium for adding blood(5%).It should be a cherry red colour at the begining.But when you are incubating blood agar under a certain temperature the colur of the medium might be changed.If the cultures are growing well in that medium giving the expected results I suppose the colour change of the medium is ok. when I was handling blood agar what I observed was that the the colour of the medium was not that much cherry red .It was a much darker red colour.By the way, in your case this colur change might be due to the temperature effect on blood cells.They get lysed when heated .But usually blood agar is converted into chocolate agar when it is heated at 80C.In my point of view,I think you should check whether the medium gives the expected growth of the organism.if so nothing to worry about the colour because when the blood cells lysed more nutrients addition will occur to the medium like internal V factors which facilitate fastidious organisms growth more
I agree with the Phil's point on specs of culture media.But as you are adding blood from a sheep or human( you can obtain from hospital blood banks) or any animal source sometimes laboratory conditions might definitely affect the colour of blood.What is commercially available is not blood .But the blood agar base. You have to find blood yourself and add into the medium .So therefore, a color change is possible as you are adding blood from a natural source.Preparing blood agar is different from preparing other microbiological culture media that we usually use in lab.Sometime colour might change depending on the organisms you are obtaining blood.That is why I mentioned about considering whether the expected result is ok
The main point is to add the blood to the base of medium after cooling to 55c in waterpath to get stable red color and if u want chocolate blood agar add the blood after adjust the base temperature to 80c (at 80c the RBCs analyse )
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