Lab method
Optochin test
P-disk: pneumococcus sensitive, viridans resistant
OP-toh-kin
High-yield clue
Zone of inhibition around the optochin P-disk means Streptococcus pneumoniae (sensitive); viridans streptococci are resistant.
Overview
A disk-based susceptibility concept using an optochin (ethylhydrocupreine) P-disk to separate Streptococcus pneumoniae from other alpha-hemolytic streptococci.
Classification
- Differential disk concept
- Alpha-hemolytic cocci
- Zone-of-inhibition readout
Lab & identification clues
- P-disk sensitivity = S. pneumoniae
- No zone = viridans (resistant)
- Complements bile solubility result
- Read on blood agar
Associations
- Pneumococcus vs viridans differentiation
- Study pairing with bile solubility
- Alpha-hemolysis workup vocabulary
Commonly confused with
- Bacitracin test
- Bile solubility test
Frequently asked questions
What is Optochin test?
A disk-based susceptibility concept using an optochin (ethylhydrocupreine) P-disk to separate Streptococcus pneumoniae from other alpha-hemolytic streptococci.
What is the high-yield clue for Optochin test?
Zone of inhibition around the optochin P-disk means Streptococcus pneumoniae (sensitive); viridans streptococci are resistant.
What is Optochin test associated with?
Optochin test is associated with Pneumococcus vs viridans differentiation, Study pairing with bile solubility, and Alpha-hemolysis workup vocabulary.
What is Optochin test commonly confused with?
Optochin test is commonly confused with Bacitracin test and Bile solubility test.
Original concept summary for coursework. Sources checked: OpenStax Microbiology 2e and NCBI Bookshelf Medical Microbiology; reviewed 2026-06. Describes vocabulary and interpretation concepts only; not a lab protocol and not for handling specimens or identifying patient isolates.