Which organism is typically optochin sensitive, aiding identification of Streptococcus pneumoniae?

Which organism is typically optochin sensitive, aiding identification of Streptococcus pneumoniae?

• A. Streptococcus pneumoniae
• B. Viridans streptococci
• C. Enterococcus faecalis
• D. Staphylococcus aureus

Answer: (A)

Optochin sensitivity is a classic lab feature used to distinguish Streptococcus pneumoniae from other alpha-hemolytic streptococci. When an optochin-impregnated disk is placed on a lawn of growth, Streptococcus pneumoniae is inhibited even at low concentrations, producing a clear zone around the disk. This is why it’s used to identify the pneumococcus. Viridans streptococci, in contrast, are resistant to optochin and do not show a zone of inhibition, which helps separate them from pneumococcus. Other organisms mentioned don’t show this same optochin-sensitive pattern, so they aren’t identified by this test.

Optochin sensitivity is a classic lab feature used to distinguish Streptococcus pneumoniae from other alpha-hemolytic streptococci. When an optochin-impregnated disk is placed on a lawn of growth, Streptococcus pneumoniae is inhibited even at low concentrations, producing a clear zone around the disk. This is why it’s used to identify the pneumococcus. Viridans streptococci, in contrast, are resistant to optochin and do not show a zone of inhibition, which helps separate them from pneumococcus. Other organisms mentioned don’t show this same optochin-sensitive pattern, so they aren’t identified by this test.