Pneumonia occurs if the organisms are inhaled into the lungs and not cleared (again, viral infection, or smoking-induced ciliary paralysis might be contributing factors). The organisms polysaccharide capsule makes it resistant to phagocytosis and if there is no pre-existing anticapsular antibody alveolar macrophages cannot adequately kill the pneumococci. The organism spreads to the blood stream (where it can cause bacteremia) and is carried to the meninges, joint spaces, bones, and peritoneal cavity, and may result in meningitis, brain abscess, septic arthritis, or osteomyelitis.S. pneumoniae has several virulence factors, including the polysaccharide capsule mentioned earlier, that help it evade a hosts immune system. It has pneumococcal surface proteins that inhibit complement-mediated opsonization, and it secretes IgA1 protease that will destroy secretory IgA produced by the body and mediates its attachment to respiratory mucosa.The risk of pneumococcal infection is much increased in persons with impaired IgG synthesis, impaired phagocytosis, or defective clearance of pneumococci. In particular, the absence of a functional spleen, through congenital asplenia, surgical removal of the spleen, or sickle-cell disease predisposes one to a more severe course of infection (overwhelming post-splenectomy infection) and prevention measures are indicatedPeople with a compromised immune system, such as those living with HIV, are also at higher risk of pneumococcal disease. In HIV patients with access to treatment, the risk of invasive pneumoccal disease is 0.2–1% per year and has a fatality rate of 8%.There is an association between pneumococcal pneumonia and influenza.
Penicillin-resistant strains are more likely to be resistant to other antibiotics. Most isolates remain susceptible to vancomycin, though its use in a β-lactam-susceptible isolate is less desirable because of tissue distribution of the medication and concerns of development of vancomycin resistance.More advanced beta-lactam antibiotics (cephalosporins) are commonly used in combination with other antibiotics to treat meningitis and community-acquired pneumonia. In adults recently developed fluoroquinolones such as levofloxacin and moxifloxacin are often used to provide empiric coverage for patients with pneumonia, but in parts of the world where these medications are used to treat tuberculosis, resistance has been described.Susceptibility testing should be routine with empiric antibiotic treatment guided by resistance patterns in the community in which the organism was acquired. There is currently debate as to how relevant the results of susceptibility testing are to clinical outcome. There is slight clinical evidence that penicillins may act synergistically with macrolides to improve outcomes.Resistant Pneumococci strains are called penicillin-resistant Pneumococci (PRP), penicillin-resistant Streptococcus pneumoniae (PRSP), Streptococcus pneumoniae penicillin resistant (SPPR), or drug-resistant Strepotococcus pneumomoniae (DRSP). History
In the 19th century it was demonstrated that immunization of rabbits with killed pneumococci protected them against subsequent challenge with viable pneumococci. Serum from immunized rabbits or from humans who had recovered from pneumococcal pneumonia also conferred protection. In the 20th century, the efficacy of immunization was demonstrated in South African miners.It was discovered that the pneumococcuss capsule made it resistant to phagocytosis, and in the 1920s it was shown that an antibody specific for capsular polysaccharide aided the killing of S. pneumoniae.