vPrinciple:-

               This test is used to identify pneumococci. Optochin lyses pneumococci.

       However, alpha-streptococci are resistant to optochin.

    v   Requirements:-

 1    Optochin disks

       2   Pure culture of suspected organisms on 5% sheep blood agar

vProcedure:-

1      Streak 2-3 suspect colonies of a pure culture onto half of a 5% sheep blood                agar.

      2    Aseptically place an optochin disk on upper third of the streaked area.

      3    Incubate the plate for 18-24 hours.

      4    Observe and measure the zone inhibition including the diameter of the disk.

v Observations:-

1     Positive: Zone of inhibition more than 14 mm in diameter with 6 mm disk: pneumococci

       2      Negative: No zone of inhibition

       3      Equivocal: Zone of inhibition less than 14 mm

 v  Quality control:-

         Use following microorganisms to confirm the reliability of reagents:

         Positive test: Pneumococci

         Negative test: alpha-streptococci