DISKS - For in vitro use only - Catalogue No. DO60

Our Optochin Disks are used to aid in the greater around the disk. Alpha-hemolytic organisms presumptive identification of producing smaller zone sizes (6 to 13-mm) should be pneumoniae from other alpha-hemolytic streptococci. tested for bile solubility; if they are bile soluble they is commonly found in can be presumptively identified as pneumococci until the human respiratory tract along with other further tests are performed. streptococci. When thought to be implicated in Other non-pneumococcal alpha-hemolytic disease, Streptococcus pneumonia can be streptococci will grow right up to the disk and show differentiated from other alpha-hemolytic streptococci no zone of inhibition. based on its susceptibility to optochin This is only a presumptive test, therefore (ethylhydrocupreine hydrochloride). The growth of additional biochemical and/or serological tests may pneumococci is markedly inhibited by optochin, need to be performed on isolated colonies from pure which results in the formation of zones of inhibition culture in order to complete identification. around disks impregnated with optochin. • Occasional, rare strains of pneumococci not inhibited by optochin have been reported Recommended Procedure • Some strains of non-pneumococcal alpha 1. Obtain a fresh, overnight culture of the alpha- streptococci have been reported to form zones of hemolytic test organism grown on blood agar. inhibition approximately 10-12-mm in diameter Ensure that it is from a pure culture and not a when light inocula was used. Therefore ensure mixed culture plate. that you are getting a confluent lawn of 2. Using a sterile swab, streak a sample of the when reading results organism onto a non-selective TSA blood in three directions to obtain a confluent lawn of bacteria. Quality Control 3. Aseptically, place an optochin disk on the agar surface using sterilized forceps or tweezers. Tap Organism Expected Results gently to ensure that the disk is adhering to the agar surface. Streptococcus pneumoniae Susceptible 4. Incubate at 35 °C in an aerobic environment ATCC 6305 Growth with zone of inhibition ≥ 14-mm supplemented with 5% CO 2. 5. Examine the growth pattern around the disk after Resistant ATCC 12384 Growth up to the disk with 24 hours of incubation. If zone of inhibition is no zone of inhibition present measure the diameter using a millimeter ruler or caliper.

Storage and Shelf Life Interpretation of Results Our Optochin Disks should be stored at -20 °C A presumptive identification of Streptococcus and protected from light. Under these conditions they pneumoniae can be made if the alpha-hemolytic have a shelf life of 52 weeks from the date of organism produces a zone of inhibition of 14-mm or manufacture.

References

1. Bowers EF, Jeffries LR. Optochin in the identification of Str. Pneumoniae. J Clin Pathol 1955; 8:58-60. 2. Bower MK, Thiele LC, Sterman BD, Schaub IG. The optochin sensitivity test: a reliable method for identification of pneumococci. J Clin Microbiol 1957; 49:641-2. 3. Ragsdale AR, Sanford JP. Interfering effect of incubation in carbon dioxide on the identification of pneumococci by optochin discs. Appl Microbiol 1971; 22:854-5. 4. Murray PR, Baron EJ, Pfaller MA, Tenover FC, Yolken RH. Manual of clinical microbiology. 7th ed. Washington, DC: ASM, 1999.

Original: September 2008 Revised / Reviewed: May 2014