Optochin Sensitivity Test: Introduction, Principle, Test Requirements, Test Procedure, Result and Interpretation and Keynotes

achaurasiya

5 years ago

Optochin Sensitivity Test: Introduction, Principle, Test Requirements, Test Procedure, Result and Interpretation and Keynotes

Introduction of Optochin Sensitivity Test

Optochin sensitivity test uses for presumptive identification of Streptococcus pneumoniae from viridans streptococci.

Principle of Optochin Sensitivity Test

Ethylhydrocupreine hydrochloride (Optochin), a quinine derivative, selectively inhibits the growth of S. pneumoniae at a very low concentration (5ug/ml). Optochin may also inhibit other viridians streptococci, but only at much higher concentrations. The test has a sensitivity of more than 95%. Optochin is water-soluble and diffuses readily into an agar medium. Therefore, filter paper impregnated with Optochin is used in a disk diffusion test format to determine the susceptibility of suspected pneumococci and thereby confirm their identity as such S. pneumoniae cells surrounding the disk are lysed owing to changes in the surface tension, and a zone of inhibition is produced.

Test Requirements for Optochin Sensitivity Test

Test organism-Alpha hemolytic streptococci
5% sheep blood agar
Optochin disk(6 mm diameter in size)-5μg
Forceps
5% CO₂incubator
Scale

Test Procedure of Optochin Sensitivity Test

Select and streak using a straight wire, three to four well-isolated colonies of the suspected organism over a blood agar.
Place an Optochin disk was over it firmly.
Incubate the plate at 35°C for 18-24 hours in a CO2 incubator (5-10% CO2).
Observe the zone of inhibition around the disk. was ≥ 14 mm around the disk, the organism was considered as S. pneumoniae.

Result and Interpretation of Optochin Sensitivity Test

Sensitive: zone of inhibition of optochin disk 14 mm or greater

Resistant: Zone of inhibition of optochin disk is less than 14 mm

Control strains

Streptococcus pneumoniae: Sensitive

Viridans streptococci: Resistant

Keynotes on Optochin Sensitivity Test

Report an identiﬁcation of S. pneumoniae, if the alpha-hemolytic colony from gram-positive cocci in pairs is catalase-negative and susceptible to optochin.
For any alpha-hemolytic colonies from gram-positive cocci in pairs that are catalase-negative but produce zone sizes with intermediate results, perform spot bile solubility test for conﬁrmation of identiﬁcation. Report as Streptococcus pneumoniae if positive.
If the organism is optochin resistant and is a catalase-negative, alpha-hemolytic colony from gram-positive cocci in pairs, report as a viridans group streptococcus.
Optochin susceptibility is an excellent test to identify S. pneumoniae, with a 99% sensitivity for encapsulated strains and 98 to 99% speciﬁcity.