This organism stains positive on Gram stain due to thick peptidoglycan layer, which absorbs crystal violet.
This bacterium has a spherical shape and usually occurs as two joined cells.
This organism has a distinctive morphology on Gram stain called “lancet-shaped” diplococci.
Characteristically, Streptococcus pneumoniae is catalase-negative, which is helpful in distinguishing Streptococcus from Staphylococcal species that are catalase- positive.
The optochin test aids in the differentiation between Streptococcus pneumoniae and Streptococcus viridans. Streptococcus pneumoniae is optochin-sensitive, meaning the growth of bacteria is inhibited around an optochin disc, while growth of bacteria that are optochin-resistant will not be affected.
Streptococcus pneumoniae can be differentiated from Streptococcus viridans based on sensitivity to lysis by bile. Streptococcus pneumoniae is bile soluble and will lyse in presence of bile, while Streptococcus viridans will not.
This bacteria is alpha-hemolytic, which causes dark green colonies on blood agar. It is caused by hydrogen peroxide produced by bacterium, which oxidizes hemoglobin to green methemoglobin.
This organism has a capsule, which has anti-phagocytic properties.
A Quellung reaction is a biochemical reaction in which antibodies bind to a bacterial capsule, allowing species with a positive Quellung reaction to be visualized under a microscope. Streptococcus pneumoniae has a positive Quellung reaction.
An IgA protease is an enzyme that cleaves certain amino acid sequences of proteins, including immunoglobulin A. Streptococcus pneumoniae releases IgA proteases which destroy IgA, leading to increased pathogenicity. Other IgA protease producers include Neisseria gonorrhoeae, Neisseria meningitidis, and Haemophilus influenzae type B.
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