Which bacterium is commonly called the pneumococcus?

Which bacterium is commonly called the pneumococcus? The answer is Streptococcus pneumoniae.

Streptococcus pneumoniae is commonly called the pneumococcus. It is a Gram-positive, typically lancet-shaped, encapsulated bacterium that often colonizes the human nose and throat without causing illness. In some circumstances it invades tissues and produces serious disease.

Pneumococcus can cause pneumonia, meningitis, bloodstream infections, sinusitis, and middle-ear infections. Its polysaccharide capsule helps it evade immune defenses, and differences among capsule types are central to vaccine design. Laboratory identification may use its characteristic alpha-hemolysis, optochin susceptibility, or bile solubility.

The name can cause confusion because Klebsiella pneumoniae also contains “pneumoniae” in its scientific name, but it is not the pneumococcus. Pneumococcal conjugate vaccines and polysaccharide vaccines protect against selected serotypes, not every strain. Antibiotic resistance, including resistance to penicillin, remains an important clinical concern.