Sorbitol MacConkey (SMAC) agar is:

Question

BlackTom AI · Accepted Answer

To approach the question, I’ll restate what SMAC stands for and what it does in laboratory use.
Option 1: 'Selective media' — While SMAC does contain bile salts and other components that inhibit many Gram-positive bacteria and some Gram-negatives, making it selective, this option omits its differential capacity. Therefore this option is incomplete.
Option 2: 'Differential media' — SMAC also differentiates organisms based on their ability to ferment sorbitol; some strains ferment sorbitol and appear pink/red, while others (notably E. coli O157:H7) do not ferment sorbitol and remain colorless. This makes SMAC differential as well. However, this option ignores its selective aspect, so it is not fully correct.
Option 3: 'Selective and differential media' — This combines both key features: the selective components (bile salts, dyes) suppress unwanted bacteria, and the differential aspect (sorbitol fermentation) allows distinction among certain enteric bacteria on the same plate. The combination aligns with the known purpose and formulation of SMAC.
Option 4: 'None of the above' — Given that SMAC indeed has both selective and differential properties, this option is inaccurate.
In summary, the correct interpretation is that SMAC agar serves dual roles: it is designed to selectively permit the growth of certain Gram-negative enterics while inhibiting others, and it differentiates organisms based on their sorbitol fermentation profile. The presence of both selective and differential characteristics is what makes the medium particularly useful for identifying specific pathogens in stool specimens. This explains why the combined description in option 3 is the accurate characterization among the choices.

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Sorbitol MacConkey (SMAC) agar is:

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