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Variants of the bile: solubility test to differentiate Streptococcus pneumoniae from other viridans group

María Ercibengoa1, María Morales1, Marta Alonso1

  • 1Biodonostia, Infectious Diseases Area, Respiratory Infection and Antimicrobial Resistance Group; Osakidetza Basque Health Service, Donostialdea Integrated Health Organisation, Microbiology Department, 20014 San Sebastian, Spain.

Future Microbiology
|August 3, 2019
PubMed

Insights

Bile-solubility testing accurately differentiates Streptococcus pneumoniae from other viridans group streptococci (VGS). This simple method uses bile salts to detect pneumococcal cell lysis, aiding in rapid identification.

Area of Science:

  • Microbiology
  • Clinical Diagnostics
  • Bacteriology

Background:

  • Accurate identification of Streptococcus pneumoniae is crucial for appropriate treatment.
  • Distinguishing S. pneumoniae from other viridans group streptococci (VGS) can be challenging with standard methods.
  • Bile salts are known to induce autolysis in pneumococcal species.

Purpose of the Study:

  • To evaluate the efficacy of bile-solubility testing in differentiating S. pneumoniae from VGS.
  • To compare different variants of bile-solubility tests for diagnostic accuracy.

Main Methods:

  • One hundred clinical VGS isolates were identified using 16S rRNA, groEL, and sodA gene sequencing.
  • Bile-solubility tests were performed using tube testing (visual and densitometric) and direct testing on blood agar plates.
  • Isolates were incubated with bile salts to observe for cell lysis.

Main Results:

  • All S. pneumoniae isolates, except one partially lysing isolate, showed complete lysis in the presence of bile salts.
  • No VGS isolates exhibited lysis when exposed to bile salts.
  • Bile-solubility tests demonstrated high accuracy in identifying S. pneumoniae.

Conclusions:

  • Bile-solubility testing is a reliable and straightforward method for distinguishing S. pneumoniae from other VGS species.
  • The technical simplicity of bile-solubility tests makes them suitable for routine clinical laboratory use.
  • This method aids in the accurate diagnosis and management of pneumococcal infections.
Keywords:
bile-solubility testoptochin resistantviridans group streptococci

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