What distinguishes Thayer-Martin medium from modified Thayer-Martin medium?

Thayer-Martin medium is a selective culture medium used primarily for the isolation of Neisseria gonorrhoeae and other Neisseria species. The distinguishing feature of modified Thayer-Martin medium is the inclusion of trimethoprim lactate. This compound acts as an antibiotic that inhibits the growth of other bacteria, allowing for a more effective isolation of Neisseria species.

While Thayer-Martin medium contains antibiotics such as vancomycin, colistin, and nystatin to suppress the growth of competing flora, the addition of trimethoprim lactate in the modified version further enhances the selectivity of the medium. This modification is particularly useful in clinical settings where Neisseria gonorrhoeae needs to be isolated from specimens that may be contaminated with a variety of other bacteria.

The other options do not accurately reflect the key differences between these two media. For example, the presence of sheep blood does not distinguish these media as neither is typically enriched with this component. Increased salt concentration is not a defining factor between the two mediums, as both maintain similar levels for osmotic balance. Finally, the absence of antibiotics does not apply, as both media contain antibiotics aimed at providing selectivity. Thus, the correct choice, which