Thayer – Main media is used for –
First, I remember that Thayer-Main agar is selective for certain bacteria. It's used in the isolation of Neisseria gonorrhoeae, which causes gonorrhea. The medium contains specific components like vancomycin, nystatin, and colistin to inhibit other bacteria and fungi. The crystal violet in it helps prevent gram-positive organisms from growing. The glucose and peptone provide nutrients, and the agar solidifies the medium.
Now, looking at possible distractors. Common options might include other bacteria like Streptococcus, Staphylococcus, or maybe even something like Salmonella. For example, if an option says "Streptococcus pyogenes," that's incorrect because Thayer-Main isn't selective for streptococci. Another option might be "Salmonella typhi," which is typically isolated on other media like SS agar. Another distractor could be "Escherichia coli," but E. coli isn't the target here either.
The clinical pearl here is that Thayer-Main is specifically for Neisseria gonorrhoeae. Students should remember that selective media have specific inhibitors for particular pathogens. Also, differentiating between media like Thayer-Main and others used for similar organisms is key.
So, putting it all together, the correct answer is Neisseria gonorrhoeae. The explanation needs to cover the selective agents in Thayer-Main, why it's used for this organism, and why other options are incorrect. Each wrong option's reasoning should address why they don't fit, maybe mentioning the specific inhibitors or the type of organism they're used for instead.
**Core Concept**
Thayer-Main agar is a selective and differential culture medium designed for the isolation of *Neisseria gonorrhoeae*, the causative agent of gonorrhea. It contains inhibitors like vancomycin, nystatin, and colistin to suppress contaminating organisms while supporting the growth of *N. gonorrhoeae*.
**Why the Correct Answer is Right**
Thayer-Main agar is specifically formulated to isolate *Neisseria gonorrhoeae* from clinical specimens like urethral or cervical swabs. The medium’s selective agents (e.g., vancomycin inhibits gram-positive bacteria, colistin inhibits gram-negative rods) and enriched nutrients (peptone, glucose) create an environment where *N. gonorrhoeae* thrives. The presence of crystal violet enhances selectivity by inhibiting gram-positive organisms further.
**Why Each Wrong Option is Incorrect**
**Option A:** *Streptococcus pyogenes* requires blood agar with specific growth factors, not Thayer-Main.
**Option B:** *Salmonella typhi* is isolated on SS agar or MacConkey agar, not Thayer-Main.
**Option C:** *Staphylococcus aureus* grows on Mannitol salt agar, which is selective for staphylococci.
**Clinical Pearl / High-Y