Which of the following is NOT a classical infectious cause of granuloma formation?

Granulomas are a specific type of inflammatory response that occur as part of the immune system's reaction to persistent irritants, including certain infections. Classical infectious causes of granuloma formation typically include fungal infections such as histoplasmosis, coccidioidomycosis, and blastomycosis. These organisms provoke a robust immune response resulting in granuloma formation as the body attempts to wall off and contain the infection.

In this context, Streptococcus pyogenes, which is responsible for diseases like strep throat and rheumatic fever, does not usually lead to granuloma formation. While it can cause inflammation, its infection mechanism does not typically elicit the same chronic granulomatous response seen with the fungi mentioned. Instead, Streptococcus pyogenes is more associated with acute, suppurative infections characterized by neutrophilic infiltration, rather than the granulomatous inflammation seen with chronic infections.

Thus, identifying Streptococcus pyogenes as not being a classical infectious cause of granuloma formation is accurate, as it does not fit the profile of pathogens typically responsible for inducing this type of immune response.