Gram Rod Postive Acid Test

[xswtxoj]

If your unknown bacteria is gram postive postive, why is the acid fast test not need to be done?

[JorgeLobo]

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.).

[Sepals]

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.

[JorgeLobo]

Gram neg stains red -= safranin - not purple.

[canalon]

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.