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Gram Rod Postive Acid Test

About microscopic forms of life, including Bacteria, Archea, protozoans, algae and fungi. Topics relating to viruses, viroids and prions also belong here.

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Gram Rod Postive Acid Test

Postby xswtxoj » Fri Feb 27, 2009 11:55 pm

If your unknown bacteria is gram postive postive, why is the acid fast test not need to be done?
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Re: Gram Rod Postive Acid Test

Postby JorgeLobo » Sat Feb 28, 2009 1:10 am

I'm not sure where you get that. If it's Gram Negative you don't need an acidfast. The acidfast bacteria are Gram positive (Mycobacterium spp. Nocardia spp.).
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Postby Sepals » Mon Mar 02, 2009 2:09 pm

Acid fast organisms such as Mycobacterium have a cell wall made up of glycolipids, in particular mycolic acids and these are resistant to acid staining, only retaining the carbol fuchsin, making them appear red and gram negative.

If the organisms look purple, then these have been decolourised and therefore do not need acid fast treatment. Gram positive would be the conclusion you draw.
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Re: Gram Rod Postive Acid Test

Postby JorgeLobo » Mon Mar 02, 2009 9:54 pm

Gram neg stains red -= safranin - not purple.
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Postby canalon » Sun Mar 08, 2009 4:18 am

To make things clearer:
Acid fast bacteria ARE gram positive, but the structure of their cell wall prevents the entry of the crystal violet. So they appear Gram negative. So if you have a gram positive, it is gram positive, no need for acid fast test. If it is Gram negative, it can be because it is a gram negative, or because it is an acid fast organism, hence the need for the test.
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