Pneumococcus and Viridans streptococci: Introduction, Differentiating Features, Keynotes, Pneumococcus, and Viridans streptococci Footages

Introduction of Streptococcus pneumoniae and Viridans streptococci

Streptococcus pneumoniae is also called pneumococcus and pneumococcus is the commensals of the upper respiratory tract. It is an important etiological agent of pneumonia and otitis media in children that differs from streptococci in its morphology (diplococci), bile solubility, optochin sensitivity, and a specific polysaccharide capsule. It is Gram-positive, small (1µm in diameter), slightly elongated cocci arranged in pairs i.e. diplococci with the broad ends in apposition.

Viridans streptococci produce alpha hemolysis on 5% sheep blood agar. Viridans means green in color. They are commensals of the mouth and upper respiratory tract. This group contains many species, like Streptococcus salivarius, Streptococcus sanguis, Streptococcus mutans, and Streptococcus milleri. They cause endocarditis and dental caries.

Differences between Streptococcus pneumoniae and Viridans streptococci

Differentiation features of pneumococcus and Viridans streptococci are as follows-

Character	Streptococcus pneumoniae	Viridans streptococci
Colony	Draughtsman	Dome-shaped
Bile solubility Test	Positive	Negative
Optochin (ethylhydrocupreine hydrochloride) 5 µg Sucsceptibility test	Sensitive	Resistant
Inulin fermentation	Positive	Negative
Mice intraperitoneally when injected	Death after 24 hours	No death
Mice intracerebrally when injected	Death after 6 hours	No death
Capsule	Present	Absent
Quellung Reaction	Positive	Negative

Keynotes

• Pneumococcus causes pneumonia and otitis media while Viridans streptococci are responsible for endocarditis and dental caries.
• The chemical name of optochin is ethylhydrocupreine hydrochloride.
• The quellung reaction is a biochemical reaction in which antibodies bind to the bacterial capsule of pneumococcus and it is also called the Neufeld reaction.
• Quellung reaction also occurs other than S. pneumoniae like K. pneumoniae, N. meningitidis, B. anthracis, H. influenzae, E. coli, and Salmonella.
• Sodium desoxycholate (bile salt) is used in bile solubility test.

Pneumococcus and Viridans streptococci Footages

Encapsulated (clear zone around the bacteria) strain of Streptococcus pneumoniae in Gram staining of CSF

Optochin Sensitive Pneumococcus Demonstration

Gram-positive diplococci in Gram staining of Streptococcus pneumoniae culture

Draughtsman colony of Streptococcus pneumoniae on blood agar demonstration

Gram-positive diplococci in Gram staining of Sputum

Numerous Gram-positive lanceolate diplococci and pus cells in sputum Gram staining

Gram-positive cocci in singles, pairs, short chains and long chains of Viridans streptococci in Gram staining of culture

Further Readings

• Bailey & Scott’s Diagnostic Microbiology. Editors: Bettey A. Forbes, Daniel F. Sahm & Alice S. Weissfeld, 12th ed 2007, Publisher Elsevier.
• Colour Atlas and Textbook of Diagnostic Microbiology. Editors: Koneman E.W., Allen D.D., Dowell V.R. Jr, and Sommers H.M.
• Cowan & Steel’s Manual for identification of Medical Bacteria. Editors: G.I. Barron & R.K. Felthani, 3rd ed 1993, Publisher Cambridge University Press.
• Jawetz, Melnick and Adelberg’s Medical Microbiology. Editors: Geo. F. Brook, Janet S. Butel & Stephen A. Morse, 21st ed 1998, Publisher Appleton & Lance, Co Stamford Connecticut.
• Clinical Microbiology Procedure Handbook Vol. I & II, Chief in editor H.D. Isenberg, Albert Einstein College of Medicine, New York, Publisher ASM (American Society for Microbiology), Washington DC.
• Mackie and Mc Cartney Practical Medical Microbiology. Editors: J.G. Colle, A.G. Fraser, B.P. Marmion, A. Simmous, 4th ed, Publisher Churchill Living Stone, New York, Melborne, Sans Franscisco 1996.
• District Laboratory Practice in  Tropical Countries  –  Part-2-   Monica Cheesebrough-   2nd Edn Update
• Manual of Clinical Microbiology. Editors: P.R. Murray, E. J. Baron, M. A. Pfaller, F. C. Tenover and R. H. Yolken, 7th ed 2005, Publisher ASM, USA
• Textbook of Diagnostic Microbiology. Editors: Connie R. Mahon, Donald G. Lehman & George Manuselis, 3rd edition2007, Publisher Elsevier.
• Topley & Wilsons Principle of Bacteriology, Virology, and immunology Vol I, II, III, IV & V. Editors: M.T. Parker & L.H. Collier, 8th ed 1990, Publisher Edward Arnold publication, London.
• Medical Microbiology-The Practice of Medical Microbiology Vol-2-12th Edn. –Robert Cruickshank