Final answer:
The capsule is the virulence factor strongly associated with Pneumococcal and Klebsiella pneumonia strains, contributing to their ability to evade the immune system and causing severe infections.
Step-by-step explanation:
The virulence factor that is strongly associated with both Pneumococcal and Klebsiella pneumonia strains is the capsule. The capsule serves not only in adhesion to host tissues but also plays a critical role in immune evasion. It acts as a barrier, protecting the bacteria from being readily phagocytosed by the immune system's cells.
Specifically, in Streptococcus pneumoniae, which causes pneumococcal pneumonia, the production of a polysaccharide capsule is a significant virulence factor. Capsulated strains of S. pneumoniae are more virulent compared to nonencapsulated strains. These encapsulated strains can invade the bloodstream, leading to septicemia and meningitis.
Klebsiella pneumoniae also possesses a capsule that enhances its ability to resist phagocytosis, contributing to its virulence and the severity of the infections it causes, which can include pneumonia and other healthcare-associated infections.