what is different between NA(Nutrient agar) and MH (Mueller Hinton agar) for do AST?

Tittle: why we do not use NA(Nutrient Agar) for AST? and why we use MH (Mueller Hinton agar) for AST?

My Answers below show:

1. NA: is a general purpose for growing variety of organism. it this media contains of beef extract and peptone allowing many organism growth well. in addition, this media have just only pH: 6.8 can not used Discs diffusion and zone is not properly. For my ideas think that this media can used for AST but the zone are not proper for CLSI (clinical laboratory standard institute). CLSI recommended that  used NA for subculture because it is easy grow on the surface, and is clearly as small colonies or for identification, purification, and isolation colonies. Especially, CLSI providing the drugs discs apply on MH plate and the drugs discs has the target. 

2. MH( Mueller Hinton agar). is used for microbiological growth medium that is commonly for AST. Moreover, There are three main property that make MH excellent for Antibiotic use:

- it is non-selective and non-differentiate medium mean that all oganisms plated on here will growing. Additionally, it contains starch. Starch is known to absorb toxins released from bacterias, so they can't interfere with the antibiotics. 

- it is a loose agar that allow for better diffusion of the antibiotics than most other plates and the better zone of inhibition.

- the other ways is used in CLSI that recommend used MH for diffusion discs and E-test. especially, MH consist of pH: 7.2 that allow organism growing well. 

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