Which medium is not appropriate for the primary isolation of Bordetella pertussis?

• A. Modified Skirrow's medium
• B. Regan-Lowe
• C. Bordet-Gengou
• D. Buffered charcoal yeast extract

Answer: (A)

The main idea here is that isolating Bordetella pertussis requires a medium that is both nutrient-rich for this fastidious organism and selective enough to suppress competing flora. A medium designed to specifically favor Campylobacter uses antibiotic components that strongly inhibit Bordetella pertussis growth. Modified Skirrow's medium contains antibiotics (and other inhibitors) that create an environment that Campylobacter can survive in but Bordetella pertussis cannot, so it is not suitable for primary isolation of pertussis.

In contrast, Bordet-Gengou agar, which uses potato infusion with blood, provides nutrients that support Bordetella pertussis growth and has a long history of successful isolation from clinical specimens. Regan-Lowe medium is a charcoal-based, selective medium that suppresses contaminating flora while allowing Bordetella pertussis to grow, making it a standard choice in pertussis workups. Buffered charcoal yeast extract is a nutrient-rich medium that, while more commonly associated with other fastidious organisms, is also described in pertussis isolation protocols in some laboratory practices.

So the medium that would misfit the goal of primary isolation due to its Campylobacter-targeted selectivity is the one designed for Campylobacter, making it inappropriate for Bordetella pertussis.