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Diagnosis of pneumococcal infection
Medical expert of the article
Last reviewed: 04.07.2025
Pneumococcal infection can be accurately diagnosed only after the pathogen has been isolated from the lesion or blood. Sputum is taken for examination in case of lobar pneumonia, blood in case of suspected sepsis, purulent discharge or inflammatory exudate in case of other diseases. Pathological material is subjected to microscopy. Detection of gram-positive lanceolate diplococci surrounded by a capsule serves as the basis for preliminary diagnosis of pneumococcal infection. Combined type-specific serums containing high titers of antibodies to all pneumococcal serotypes are used to establish whether the isolated diplococci belong to pneumococci. In the first days of pneumococcal meningitis, the pathogen can be detected in the cerebrospinal fluid, where it is located both extra- and intracellularly.
In order to isolate a pure culture, the material to be studied is sown on blood, serum or ascitic agar. On nutrient media, pneumococcus produces small transparent colonies. A biological sample can be used to isolate a pure culture. For this purpose, white mice are intraperitoneally infected with the material to be studied. If pathogenic pneumococci are present in the material, the mice die within 24-48 hours. Solid-phase immunoelectrophoresis and PCR can be used to detect pneumococcal antigens.
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