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OPTOCHIN DISCS

Code: DD0001

For the differentiation of Streptococcus pneumoniae.

Contents
1 cartridge. containing 50 discs.

Description
Bowers and Jeffries¹ have shown that there is complete correlation between bile-solubility and full `Optochin’ susceptibility for the differentiation of Streptococcus pneumoniae from other streptococci. Oxoid `Optochin’ Discs are paper discs ready impregnated with `Optochin’ (ethylhydrocuprein hydrochloride) which provide a convenient and reliable alternative to the bile-solubility test. Pneumococci are sensitive to `Optochin’ so that a culture shows a zone of inhibition around the impregnated disc, whilst streptococci either grow right up to the edge of the disc or, occasionally, show a very small zone of inhibition.

Technique
Streak a pure culture of the organism to be tested across one half of a Blood Agar plate (Blood Agar Base CM0055 with 7% sterile blood) and apply an `Optochin’ Disc immediately before incubation. At the same time apply a second `Optochin’ Disc to the other half of the plate, previously streaked with a known pneumococcus, in order to provide a positive control. After incubation, pneumococci show a zone of inhibition at least 4 mm from the edge of the disc, whilst streptococci are completely resistant or show a small zone of inhibition extending not more than 2 mm from the edge of the disc.
Oxoid `Optochin’ Discs may also be placed on the primary culture plate, before incubation, in order to provide rapid indication of the presence of large numbers of pneumococci.

Quality Control
See under Technique.

Reference
1 Bowers E. F. and Jeffries L. R. (1955) J. Clin. Path. 8. 58.