STREPTOCOCCUS PNEUMONIAE. STREPTOCOCCUS PNEUMONIAE Pneumococcus or streptococcus pneumoniae is a common host found in the mucosa of the mouth and pharynx. Under certain conditions, it can become the causal agent of pneumonia, meningitis, septicemia and otitis. Pneumococci are small round-shaped Gram-positive bacteria which generally form pairs (diplococci). They have a protective capsule preventing phagocytosis. SEM 7800x.