Which organism is commonly identified by Thayer-Martin medium as smooth gray translucent colonies after 3 days and is a gram-negative diplococcus?

Which organism is commonly identified by Thayer-Martin medium as smooth gray translucent colonies after 3 days and is a gram-negative diplococcus?

• A. Neisseria meningitidis
• B. Neisseria gonorrhoeae
• C. Streptococcus agalactiae
• D. Staphylococcus aureus

Answer: (B)

Thayer-Martin medium is a selective medium designed to isolate pathogenic Neisseria species, especially Neisseria gonorrhoeae, by inhibiting many other bacteria and fungi. Neisseria gonorrhoeae on this medium forms small, smooth, gray translucent colonies within a couple of days. Microscopically, Neisseria are gram-negative diplococci, typically seen as paired cocci. This combination of selective growth, colony appearance, and the characteristic gram-negative diplococcus shape is why Neisseria gonorrhoeae is the organism described. The other organisms are gram-positive cocci and do not grow with this colony morphology on Thayer-Martin, so they don’t fit the description.

Thayer-Martin medium is a selective medium designed to isolate pathogenic Neisseria species, especially Neisseria gonorrhoeae, by inhibiting many other bacteria and fungi. Neisseria gonorrhoeae on this medium forms small, smooth, gray translucent colonies within a couple of days. Microscopically, Neisseria are gram-negative diplococci, typically seen as paired cocci. This combination of selective growth, colony appearance, and the characteristic gram-negative diplococcus shape is why Neisseria gonorrhoeae is the organism described. The other organisms are gram-positive cocci and do not grow with this colony morphology on Thayer-Martin, so they don’t fit the description.