Staphylococcus aureus can be isolated from stool cultures by using which type of medium?

Staphylococcus aureus is a halophilic organism, meaning it thrives in high-salt environments. The medium with 7.5% salt concentration is particularly conducive to isolating S. aureus because this high salt level inhibits the growth of many other types of bacteria, allowing Staphylococcus aureus to proliferate in the culture. This selective pressure means that when using this medium, the growth of competing flora from stool samples is suppressed, and S. aureus can be effectively isolated for further study or identification.

In contrast, potassium tellurite medium is generally used for isolating diphtheroids and not specifically for Staphylococcus. McConkey agar is selective for Gram-negative bacteria, making it unsuitable for isolating Gram-positive organisms like S. aureus. Lowenstein-Jensen medium is primarily designed for the culture of Mycobacterium species and would not support the growth of S. aureus. Thus, the option with a 7.5% salt concentration is the most appropriate choice for isolating Staphylococcus aureus from stool cultures.