Laboratory diagnosis, Treatment and Prevention of Streptococcus pneumoniae

Laboratory diagnosis of Streptococcus pneumoniae

Specimen: Sputum, blood, endotracheal aspirate, bronchoalveolar lavage, cerebrospinal fluid (CSF), pleural fluid, joint fluid, abscess fluid, bones, and other biopsy material.


  • Gram staining of sputum shows lancet shaped Gram-positive cocci in pairs.
  • Fresh emulsified sputum mixed with antiserum causes capsule swelling (the quellung reaction) for identification of pneumococci.
  • In acute pneumococcal otitis media, Gram stain of an aspirated fluid smear from middle ear is useful to demonstrate the bacteria.


  • Sputum or blood is plated on blood agar and incubated at 37° C in the presence of 5–10% carbon dioxide.
  • Gray colonies with alpha-hemolysis are observed after overnight incubation.
  • Diagnosis of pneumococcal meningitis is confirmed by CSF culture.

Identification of bacteria

  • Optochin sensitivity test
    • S. pneumoniae is identified by its sensitivity to optochin (ethylhydrocupreine dihydrochloride).
    • The isolate is streaked onto a blood agar plate and a disk saturated with optochin is placed in the middle of the inoculum.
    • A zone of inhibited bacterial growth is seen around the disk after overnight incubation.
  • Bile solubility test
    • It detects an autolytic enzyme, amidase, present in pneumococci, which breaks the bond between alanine and muramic acid of the peptidoglycan of the pneumococcal cell wall.
    • Isolates of S. pneumoniae are lysed rapidly when the autolysins are activated after exposure to bile.
    • Thus the organism can be identified by placing a drop of bile on an isolated colony.
  • Inulin fermentation test
    • It ferments inulin and hence differentiate it from other streptococci.

Animal inoculation

  • S. pneumoniae can be isolated from clinical specimens containing few pneumococci by intraperitoneal inoculation in mice.
  • Pneumococci are demonstrated in the peritoneal exudate and heart blood of the mice, which die 1–3 days after inoculation.

Antigen detection

  • Pneumococcal C polysaccharide is excreted in urine and can be detected using a commercially prepared immunoassay.
  • The CIEP is a useful test to detect pneumococcal capsular polysaccharide antigen in the CSF for diagnosis of meningitis, and in the blood or urine for diagnosis of bacteremia and pneumonia.
  • Latex agglutination test using the latex particles coated with anti-CRP antibody is employed to detect C reactive protein.
  • The CRP is used as a prognostic marker in acute cases of acute pneumococcal pneumonia, acute rheumatic fever, and other infectious diseases.

Antibody detection

  • The indirect hemagglutination, indirect fluorescent antibody test, and ELISA are used to demonstrate specific pneumococcal antibodies in invasive pneumococcal diseases.

Nucleic Acid–Based Tests

  • Nucleic acid probes and PCR assays are used for identification of S. pneumoniae isolates in culture.

Laboratory diagnosis, Treatment and Prevention of Streptococcus pneumoniae

Treatment of Streptococcus pneumoniae

  • Most pneumococci are susceptible to penicillin.
  • Other antibiotics, such as macrolides or selected fluoroquinolones with activity against pneumococci, are available for patients who are allergic to penicillin.
  • Penicillin-resistant pneumococci are being increasingly documented.
  • The mechanism of this resistance is an alteration of one or more of the bacterium’s penicillin-binding proteins (PBPs) rather than production of beta-lactamase.
  • Most resistant strains remain sensitive to third generation cephalosporins (such as cefotaxime or ceftriaxone), and all are still sensitive to vancomycin.
  • For serious pneumococcal infections, treatment with a combination of antibiotics is recommended. Vancomycin combined with ceftriazone is used commonly for empiric treatment, followed by monotherapy with an effective cephalosporin, fluoroquinolone or vancomycin.
  • Ceftriaxone can be used for meningitis caused by ceftriaxone-susceptible pneumococci.
  • Amoxicillin is the drug of choice for treatment of otitis media, sinusitis, and pneumonia caused by penicillin-resistant pneumococci with intermediate resistance.
  • Ceftriaxone is the drug of choice for non-CNS invasive pneumococcal diseases caused by penicillin- and ceftriaxone resistant pneumococci.
  • Vancomycin is used if the pneumococcus is resistant to ceftriaxone.

Prevention and control of Streptococcus pneumoniae

  • Pneumococcal vaccines: 23 valent pneumococcal polysaccharide vaccine (PPSV23) and polyvalent pneumococcal conjugate vaccine (PCV13) play an important role in prevention of pneumococcal diseases.
  • Personal hygiene is another important factor.

About Author

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Sagar Aryal

Sagar Aryal is a microbiologist and a scientific blogger. He attended St. Xavier’s College, Maitighar, Kathmandu, Nepal, to complete his Master of Science in Microbiology. He worked as a Lecturer at St. Xavier’s College, Maitighar, Kathmandu, Nepal, from Feb 2015 to June 2019. After teaching microbiology for more than four years, he joined the Central Department of Microbiology, Tribhuvan University, to pursue his Ph.D. in collaboration with Helmholtz-Institute for Pharmaceutical Research Saarland (HIPS), Saarbrucken, Germany. He is interested in research on actinobacteria, myxobacteria, and natural products. He has published more than 15 research articles and book chapters in international journals and well-renowned publishers.

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