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Optochin test

Microbiology

Principle

S. pneumoniae is inhibited by ethylhydrocupreine (optochin); viridans streptococci are resistant.

Procedure

Streak an alpha-hemolytic colony on blood agar, place a 6 mm optochin disk and incubate at 35 °C in 5% CO2 overnight.

Results

Zone of 14 mm or more: susceptible = S. pneumoniae
Smaller zone: confirm with bile solubility

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