Streptococcus pneumoniae (pneumococci) are gram-positive, alpha-hemolytic, aerobic, encapsulated diplococci. In the US, pneumococcal infection annually causes about 7 million cases of otitis media, 500,000 cases of pneumonia, 50,000 cases of sepsis, 3,000 cases of meningitis, and 40,000 deaths. Diagnosis is by Gram stain and culture. Treatment depends on the resistance profile and includes either a beta-lactam, a macrolide, a respiratory fluoroquinolone, or sometimes vancomycin .
Pneumococci are fastidious microorganisms that require catalase to grow on agar plates. In the laboratory, pneumococci are identified by
Gram-positive lancet-shaped diplococci
Catalase-negative
Alpha-hemolysis on blood agar
Sensitivity to optochin
Lysis by bile salts
Pneumococci commonly colonize the human respiratory tract, particularly in winter and early spring. Spread is via airborne droplets.
True epidemics of pneumococcal infections are rare; however, some serotypes seem to be associated with outbreaks in certain (eg, military, institutional) populations.