Mueller-Hinton agar

Bob bbruner at
Thu Dec 7 20:48:22 EST 2000

On Thu, 07 Dec 2000 15:26:00 GMT, "Frederic Langlois"
< at> wrote:

>I finally found out (to late I guess since my exam was last week) that
>Mueller-Hinton media doesn't contain PABA (para aminobenzoic acid) which
>interferes with antibiotic diffusion in the medium.

That is not quite correct -- but it is warm. Yes, one aspect of MH is
that it is low in PABA. That does interfere with assay of sulfa drugs,
because sulfa drugs are PABA analogs. It is not reasonable to suggest
that PABA interferes with drug diffusion, but it does reduce the
activity, simply by competition. 

This sent me back to my old Difco manual, which has a nice discussion
of MH. The basic point stands that MH has become a standard. Yes, not
one randomly chosen, but one developed with some care, and useful over
quite a range of drugs. You could use something else if you wanted to,
for some reason, but you would not be able to compare your results
with those from others. Further, there is presumably some quality
control with manufacture of MH that will tend to make it more
reproducible in key aspects.


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