Final answer:
S. pneumoniae primarily invades the human respiratory tract causing pneumococcal pneumonia and meningitis. Diagnosis involves gram-stained specimens or cultures, and while antibiotics are the main treatment, resistance is a growing problem thus making vaccination a critical preventive measure.
Step-by-step explanation:
S. pneumoniae, also known as pneumococcus, is a bacterium that primarily invades the human respiratory tract, causing diseases such as pneumococcal pneumonia and pneumococcal meningitis. It is often present in the microbiota of the pharynx, especially in young children. The bacterium can invade different parts of the body such as the bronchioles and alveoli in the lungs and can even cross the blood-brain barrier causing meningitis. The presence of a polysaccharide capsule and various virulence factors including pneumolysins, PI-1 pilin, and PavB help it adhere to host cells and evade the immune system. Diagnosis of S. pneumoniae infections can be done using gram-stained specimens of cerebrospinal fluid (CSF) or blood cultures. The bacteria can be identified as gram-positive, lancet-shaped diplococci. Antibiotic treatment is the mainstay for combating pneumococcal infections, but resistance to common antibiotics such as ß-lactams, macrolides, and fluoroquinolones is on the rise. Vaccination is a key prevention strategy, with PCV13 and PPSV23 vaccines available to protect vulnerable populations.