It typically contains:
- 2.0g beef extract
- 17.5g casein hydrolysate
- 1.5g starch
- 17.0g agar
- dissolved in 1 liter of distilled water.
- pH adjusted to neutral at 25 °C.
Five percent sheep blood and nicotinamide adenine dinucleotide may also be added when susceptibility testing is done on Streptococcus species. This type is also commonly used for susceptibility testing of Campylobacter.
It has a few properties that make it excellent for antibiotic use. First of all, it is a nonselective, nondifferential medium. This means that almost all organisms plated on it will grow. Additionally, it contains starch. Starch is known to absorb toxins released from bacteria, so that they cannot interfere with the antibiotics. Second, it is a loose agar. This allows for better diffusion of the antibiotics than most other plates. A better diffusion leads to a truer zone of inhibition.
- "Susceptibility testing of Salmonella using disk diffusion" (PDF). World Health Organization. July 2002. p. 9. Retrieved 12 May 2016.
- Mueller, J. H.; Hinton, J. (1 October 1941). "A Protein-Free Medium for Primary Isolation of the Gonococcus and Meningococcus". Experimental Biology and Medicine. 48 (1): 330–333. doi:10.3181/00379727-48-13311.
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