Colistin-nalidixic acid agar (CNA) is primarily utilized for the isolation of which type of bacteria?

Colistin-nalidixic acid agar (CNA) is designed specifically to enhance the isolation of gram-positive cocci, particularly Staphylococcus species, by inhibiting the growth of most gram-negative bacteria. The selective agents, colistin and nalidixic acid, effectively suppress the growth of undesired organisms, allowing for better isolation and identification of Staphylococcus.

This agar medium is especially useful in clinical settings where it is important to differentiate and isolate Staphylococcus species from mixed flora that might be present in samples. The formulation encourages the growth of these bacteria while minimizing contamination from other types of bacteria, making it a valuable tool for microbiologists.

In contrast, the other options listed do not align with the primary use of CNA. Neisseria species, Enterobacteriaceae, and Pseudomonas aeruginosa may require different selective media for optimal isolation and identification, as they do not thrive on CNA due to the inhibitory conditions it creates.