I have Mueller-Hinton broth (CM0405, OXOID). However as stated in all CLSI documents, I should prepared it to be "cation-adjusted Mueller Hinton broth (CAMHB)" for fastidious bacteria. In the documents, it stated 'Prepare MHB according to the manufacturer’s recommendations, autoclave, and before adding supplemental cations'. Based on the fact that these cations are not volatile compounds, and heating by autoclave will help to dissolve the cations in the broth, can I add the supplemental cations before autoclave? So that I could check for the pH before autoclave. Then my pH meter will not introduce any contamination in the broth if I do this. What do you think?
Cation solutions (Ca, Mg, Mn or Fe, Na as you may be using) are always filter sterilized and added to autoclaved and cooled media afterwards- to avoid precipitation. Also they are NOT volatile and when added later do NOT bring any noticeable pH changes. Thus, afterwards pH adjustment/ probe contamination is out of question. This is from experience and reading! Thanks,
Supplemental cations (calcium and magnesium) should be filter-sterilised before addition to the sterilised MHB. Otherwise, you can buy cation-adjusted MHB which does not require supplementation with calcium and magnesium (and therefore filter-sterilisation).
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