Bile Solubility Test- Principle, Procedure, Types, Results, Uses


Bile solubility test is a biochemical test used for the differentiation and confirmation of Streptococcus pneumoniae from other alpha-hemolytic Streptococci .

Streptococcus pneumoniae is a Gram-positive, catalase-negative, lancet-shaped coccus that causes pneumonia, meningitis, otitis media, sinusitis, and other infections. It is also known as pneumococcus and is one of the most common causes of bacterial meningitis in adults and children.

The bile solubility test has been used as an essential test for the differentiation of S. pneumoniae as it allows the distinction between the two species S. pneumoniae and Streptococcus pseudopneumoniae, which is a challenging task.

The test is based on the lysis of the bacterial cells in the presence of certain bile salts like sodium desoxycholate under certain conditions. The organisms that lyse are considered positive, whereas those that do not are considered negative .

The exact working mechanism of the test is still not clearly understood, but it has been hypothesized that the lysis is brought about by the induction of autolytic enzymes .

The bile solubility test is generally considered to be an accurate test for differentiating S. pneumoniae from other mitis group streptococci, including S. pseudopneumoniae.

The test results from the method are, however, difficult to interpret, particularly because it is based on subjective human evaluation.

The bile solubility test can be performed using a cell suspension on a slide or in a tube or by adding the reagent directly to the colony .

The following sections will describe the objectives, principle, microorganisms tested, media, reagents, and supplies used, procedure, quality control, result interpretation, reporting results, uses, and limitations of the bile solubility test.