phenol red

Chrystophylax conner at wingate.edu*nospam*
Thu Jul 30 00:01:30 EST 1998

Actually, my work (for now) is with a fungus, N. crassa.  A 'net friend
asked me this question, I will try to get some more details.

My media needs, btw, are very simple!  Minimal (for neurospora) and TSA/TSB
are all I ever use.

But thank you so much for your answer!


Yersinia wrote in message <199807300222.WAA18885 at pop.cybernex.net>...
>Chrystophylax writes,
><Why does media for nitrifying bacteria contain phenol red?
>I'm working with nitrifying bacteria.  I've based my media for them on
>literature surveys; most media formulas contain phenol red.  Why is this
>compound necessary when pH meters are available?  How would phenol red
>affect bacteria?
>I hate to tell him that I have no idea, can anyone offer any suggestion?>
>I'd be curious to know about your experiments and the media formulations
>you're using. I've spent the last year doing zillions of bacterial
>identifications, including many tests for nitrate reduction. To do these
>nitrate reduction tests, I inoculate a tube of nitrate broth, incubate it
>overnight and then add reagents (unless, of course I see bubbles in the
>inverted Durham tube, in which case I know that the organism reduced the
>nitrate to nitrogen) - sulfanilic acid and alpha naphthol. Well, when I
>saw your post here, I looked up the ingredients of nitrate broth, and it
>contains *no* phenol red - only beef extract, peptone and of course
>potassium nitrate.
>Like I said, I don't know what experiments you're doing or what you're
>growing your bugs on, but if you want to know about nitrate reduction in
>general, nitrites (a product of nitrate reduction - it goes NO3  to NO2
>to N2) are colorless - but in an acid environment (such as my above
>mentioned nitrate reduction testing, when I add the sulfanilic acid and
>alpha naphthol, they will turn the broth red.
>I'm familiar with phenol red as an additive to other media, usually to
>indicate whether or not an organism ferments a sugar to an alcohol to an
>acid, or an alcohol to an acid. Such characteristics are used to make
>identifications of microorganisms. As to why put phenol red in media
>rather than use a pH meter, I would think it's much easier and cleaner to
>look at the plate and see the yellow color than to contaminate a pH
>electrode measuring the pH of a medium containing bacteria just to see if
>the pH is acidic. Besides, I don't think they had pH meters at the time
>these media were originally being formulated.  ;-)
>I hope I helped a little, anyway. Good luck with your experiments!
>"If you're not part of the solution, you're part of the precipitate."

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