Cat. no. Z7011 Optochin Differentiation Disks 1 x 50 disks/cartridge
Cat. no. Z7015 Optochin Differentiation Disks 5 x 50 disks/cartridge


Hardy Diagnostics Optochin Differentiation Disks are recommended for use in the presumptive identification of Streptococcus pneumoniae from other alpha-hemolytic streptococci.


Streptococcus pneumoniae is found commonly in the human respiratory tract flora, as are other streptococci. When implicated in disease states and isolated onto blood agar for identification, the hemolytic pattern this organism gives is not distinguishable from other alpha-hemolytic streptococci. Thus, differentiation and identification must be performed via biochemical and serological testing.

Sensitivity to optochin (ethylhydrocupreine hydrochloride) is a well established phenomenon for Streptococcus pneumoniae.(5) A positive presumptive identification of S. pneumoniae is made when a well defined zone of inhibition results around the impregnated disk. Other alpha-hemolytic streptococci do not display this clear zone of inhibition when in the presence of optochin.


Each disk is impregnated with a solution of ethylhydrocupreine hydrochloride.


Storage: Upon receipt, store at -20 to 8ºC. away from direct light. The disks should not be used if there are any signs of deterioration, discoloration, or if the expiration date has passed. Protect from light, excessive heat, and moisture.



Specimen Collection: This product is not intended for primary isolation of patient specimens. This product is used in conjunction with other biochemical tests to identify cultures of isolated organism in pure culture.


1. Using an inoculating loop, select three to four well-isolated colonies of the alpha-hemolytic organism to be tested. An 18-24 hour culture (either BHI Broth, Cat. no. R20 or TSB, Cat. no. R30) of isolated organism can also be used for testing.

2. Streak the isolate onto one-half of a TSA-5% sheep blood agar plate (Cat. no. A10) so as to obtain confluent growth.(8)

Important: Use of media other than TSA-5% sheep blood agar is not recommended, as false identification may result.

3. Using sterile forceps, place an optochin disk onto the inoculated surface of the agar.

4. Press disk gently with the sterile forceps or loop so that the disk adheres firmly to the agar surface.

5. Incubate the plate at 35 +/- 2.0ºC. for 18-24 hours in 5-10% CO2 enriched environment.(8)

6. If zone of inhibition is present, measure the diameter with a millimeter ruler or caliper.


A presumptive identification for S. pneumoniae can be made if the alpha-hemolytic colony produces a zone of inhibition of 14mm or greater around the disk. Organisms producing smaller zone sizes should be tested for bile solubility. Organisms with questionable zone sizes (6-14mm) around the disk should be presumptively identified as a pneumococci only if it is bile soluble.(2)

A non-pneumococcal alpha-hemolytic streptococci should grow right up to and under the optochin disk.


It has been shown that other strains of alpha-hemolytic streptococci may show a slight susceptibility to optochin.

Optochin susceptibility is a presumptive test only. It is recommended that further biochemical tests be performed for complete identification.

Many isolates will show indeterminate zones on media other than TSA-sheep blood agar. Isolates showing the indeterminate zones would require further testing to identify them as S. pneumoniae.(8)

S. pneumoniae isolates should be incubated in a CO2 enriched environment, as some isolates will grow poorly or not at all aerobically.(8)


Standard microbiological supplies and equipment such as loops, incinerators, CO2 incubators, swabs, and culture media, etc., as well as serological and biochemical reagents, are not provided.


Test Organisms Zone Diameter
Streptococcus pneumoniae
ATCC ® 6305
> 14mm
Streptococcus pyogenes ATCC® 19615 No zone

User Quality Control

Physical Appearance

HardyDisk™ Optichin Differentiation Disks are 6mm (in diameter) filter paper disks with the letters OP printed on both sides and should appear white in color.


Optochin-sensitive (zone > 14mm)
Streptococcus pneumoniae (ATCC® 6305) growing around a HardyDisk™ Optochin Differentiation Disk (Cat. no. Z7011) on Blood Agar (Cat. no. A10). Incubated in CO2 for 24 hours at 35ºC.


Optochin-resistant (no zone)
Streptococcus pyogenes (ATCC ® 19615) growing around a HardyDisk™ Optochin Differentiation Disk (Cat. no. Z7011) on Blood Agar (Cat. no. A10). Incubated in CO2 for 24 hours at 35ºC.


1. Commission on Laboratory Accreditation, Laboratory Accreditation Program Microbiology Checklist. College of American Pathologists. Rev. 9/30/2004.

2. Jorgensen., et al. Manual of Clinical Microbiology, American Society for Microbiology, Washington, D.C.

3. Tille, P., et al. Bailey and Scott's Diagnostic Microbiology, C.V. Mosby Company, St. Louis, MO.

4. Isenberg, H.D. Clinical Microbiology Procedures Handbook, Vol. I, II & III. American Society for Microbiology, Washington, D.C.

5. J. Exp. Med. 1915; 22:269.

6. Koneman, E.W., et al. Color Atlas and Textbook of Diagnostic Microbiology, J.B. Lippincott Company, Philadelphia, PA.

7. Ragsdale, A.R. and Sanford, J.P. 1971. Appl. Microbiol.; 22:854-855.

8. Gardam, M.A. and M.A. Miller. 1998. J. Clinical Micro.; 63:3.

9. Centers for Medicare and Medicaid, Appendix C, Survey Procedures and Interpretive Guidelines for Laboratories and Laboratory Services. Subpart K - Quality System for Non-Waived Testing. 493;1200-1265. www.cms.hhs.gov/clia.

ATCC is a registered trademark of the American Type Culture Collection.