- Optochin (ethylhydrocupreine hydrochloride), a quinine derivative, has a detergent-like action and causes selective lysis of pneumococci.
- A sterile disk impregnated with optochin is placed on the first sector of an isolation plate before incubation. A zone of inhibition (area with no growth) of 14 mm or more in diameter will be seen around the disk after incubation if the organism is Streptococcus pneumoniae.
- Other alpha-hemolytic streptococci are resistant to (not killed by) optochin. Their colonies will thus grow right up to the disk of optochin or have zones of inhibition less than 14 mm in diameter.
Streptococcus-Optochin Sensitivity Testing
