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resazurin and cysteine in the media for anaerobic bacteria - basic question (Sep/08/2008 )

I started to cultivate an anaerobic bacteria.
I found that cysteine is used as reducing agent, and resazurin as indicator.

Would you kindly explain to me the meanings of the colors of the media?

For example, the color of the media with resazurin after adding cysteine is mainly pale pink, but sometimes it's dark pink or colorless.
I heard the pale pink is the correct color to be used, but please explain what's wrong with dark pink or colorless of the media.
Moreover when I let it stand the colorless media for two days, I found it turned into pale pink.
Can I use the media then?

How long do you wait for inoculation after cysteine addition?

I know these are very basic questions, but I couldn't find satisfactory answers when I goggled it. wacko.gif

Thank you for your replies in advance.


I don't use resazurin in solid media, but I do use it as an indicator in my anerobic chamber -- it starts off pink (indicating the presence of oxygen) and bcomes clear overnight (indicating anerobic conditions). If the tube in the chamber ever turns from clear to pink, we know we have oxygen in the chamber, and will flush it.

I've never found any need to wait after the addition of cysteine to media before innoculating. For example, we routinely supplement proteose peptone - yeast extract liquid media with iorn, vitamin K, glucose, K2HPO4, and cysteine. If I can, I will usually place this media in the chamber overnight to inoculate in the morning or the next afternoon, but I have (on countless occasions) just inoculated freshly prepared (and thus aerobic) media with growth off a plate, put the tubes (of Bacteroides fragilis) in the chamber, and they're grown fine by morning. For solid media, we just use the plates -- they're just BHI plates with iorn and vitamin K added -- no cysteine, no resazurin -- and they work fine.