Final answer:
S. pneumoniae resists host defenses through virulence factors like PI-1 pilin, PavB, and choline-binding proteins for adherence, disruption of immune response, and a capsule that prevents phagocytosis.
Step-by-step explanation:
S. pneumoniae, or pneumococcus, combats host defenses through various virulence factors. These factors include PI-1 pilin and PavB, which assist in bacterial adherence to host cells, specifically for colonization in the respiratory tract. Another significant element is the choline-binding protein (cbpA), which binds to epithelial cells and disrupts the function of immune factors like IgA and C3. Perhaps most notably, S. pneumoniae's capsule plays a crucial role in evading the immune system by hindering phagocytosis. As the capsule constitutes a barrier that deters immune cells from adhering and consuming the pathogen, it also enlarges the bacterial cell, making them harder to engulf.
A potent cytoplasmic toxin, pneumolysin, induces an inflammatory response, which is another strategy by which S. pneumoniae resists the human immune defenses. These strategies collectively enable S. pneumoniae to survive within the host and contribute to its ability to cause diseases such as pneumonia, septicemia, and meningitis. Confronted with this pathogen's ability to resist standard treatments, healthcare providers often resort to alternative antibiotics when resistance to first-line drugs like penicillin arises. Preventative measures include vaccinations with pneumococcal conjugate vaccine (PCV13) and pneumococcal polysaccharide vaccine (PPSV23), most commonly administered to children under two years of age and adults over 65.