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Biochemical Test

Optichin Test
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Optichin Test

The optochin test is a presumptive test that is used to identify strains of Streptococcus pneumoniae. Optochin disks are placed on inoculated blood agar plates. Because S. pneumoniae is not optochin resistant, a zone of inhibition will develop around the disk where the bacteria have been lysed. This zone is typically 14mm from the disk or greater.

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Procedure to carry out Optochin test:

 

  • Pure Colony

o    Streak a blood plate with the organism to be tested.

o    Place an optochin disc in the centre of the inoculum.

o    Incubate at 35-37C for 18-24h in 5% CO2.

o    Examine for zones of inhibition.

 

Positive result zone of inhibition of ≥5mm radius from the edge of the disc eg. Test organism is S. pneumoniae.

Negative result no zone of inhibition, or a zone ‹5 mm radius from the edge of the disc eg. Test organism is not S. pneumoniae.