– The organism is Haemophilus influenzae type b (requires X and V factors). Its polyribosylribitol phosphate (PRP) capsule is the major virulence factor for invasive disease (meningitis, epiglottitis). IgA protease (B) facilitates mucosal colonization but not invasion. Exotoxin A is from Pseudomonas . M protein is from Strep. pyogenes .