Question

Medical Microbiology

What physiological tests are necessary to differentiate the groups of alpha-hemolytic streptococci from one another? Which Lancefield groups contain alpha-hemolytic streptococci?

Answer 1

TESTS REQUIRED TO DIFFERENTIATE.

1. Isolation on Blood agar

Pneumococci frequently requires media which is enriched and increased CO2 tension for the initial isolations. They are mostly isolated on Blood agar and is incubated in a candle jar (a closed container in which a lit candle is placed to remove O2 and increase CO2 ) at 37C. On Blood agar, colonies appear small, shiny, and translucent. They are surrounded by a zone of alpha hemolysis Due to the process of autolysis with age, the colonies may show a depressed center with an elevated rim.

2. Optochin sensitivity

Pneumococci are the only streptococci that is sensitive to the drug optochin (ethylhydrocupreine hydrochloride). This is possible to be detected by a zone of inhibition around a Taxo P® disc, a paper disc containing the drug optochin, which is placed on the Blood agar plate prior to incubation.

3. Bile solubility test

Most colonies of S. pneumoniae dissolves within a few minutes when a drop of bile is placed upon them.

4. Gram stain of sputum

Streptococcus pneumoniae will usually appear as encapsulated, Gram-positive, lancet-shaped diplococci.

There are beta-hemolytic strains of each of the three species, and the strains may possess one of four different Lancefield group antigens or no group antigen. ... Non-beta-hemolytic varieties of each of the three species are grouped into the general classification of viridans streptococci.