Ethylhydrocupreine HCl susceptibility test is a presumptive identification test for which organism?

Ethylhydrocupreine HCl susceptibility test is a presumptive identification test for which organism?

• A. Viridans streptococci
• B. Streptococcus pyogenes
• C. Streptococcus agalactiae
• D. Streptococcus pneumoniae

Answer: (D)

The ethylhydrocupreine HCl susceptibility test, known as the optochin test, is used to distinguish Streptococcus pneumoniae from viridans group streptococci among alpha-hemolytic cocci. Pneumococcus is inhibited by optochin, so on a blood agar plate a clear zone around the optochin disk indicates sensitivity and points to Streptococcus pneumoniae. Viridans streptococci are resistant and grow up to the disk. This makes the test a presumptive identification for Streptococcus pneumoniae. For confirmation, bile solubility can be used, as Streptococcus pneumoniae is bile soluble while viridans streptococci are not.

The ethylhydrocupreine HCl susceptibility test, known as the optochin test, is used to distinguish Streptococcus pneumoniae from viridans group streptococci among alpha-hemolytic cocci. Pneumococcus is inhibited by optochin, so on a blood agar plate a clear zone around the optochin disk indicates sensitivity and points to Streptococcus pneumoniae. Viridans streptococci are resistant and grow up to the disk. This makes the test a presumptive identification for Streptococcus pneumoniae. For confirmation, bile solubility can be used, as Streptococcus pneumoniae is bile soluble while viridans streptococci are not.