J Clin Pathol Qual Control.
1999 Dec;21(2):275-280.
Evaluation of Optochin Disk Test for the Presumptive Identification of Streptococcus pneumoniae
- Affiliations
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- 1Department of Clinical Pathology , Yonsei University Wonju College of Medicine, Wonju, Korea.
Abstract
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BACKGROUND: To determine the optimal media and procedures of optochin test for presumptive identification of Streptococcus pneumoniae, we measured inhibition zones in various conditions.
METHODS
Each swab suspended with 0.5% MacFarland turbidity of 58 S. penumoniae and 11 alpha-hemolytic streptococci was inoculated into six kinds of media with difference in blood type (5% sheep blood vs. 5% human blood), media composition (Trypticase soy agar [TSA] vs. Mueller Hinton agar [MHA]), and media depth (3 mm vs. 4 mm). Additionally, a few colonies of tested organisms were streaked into TSA with 3 mm depth of media. After overnight incubation at 35degrees C in both of 5% CO2 and aerobic condition, inhibition zones were measured and a zone of > or =14 mm was interpreted as susceptible. Latex agglutination test was done by Slidex pneumo-kit to confirm S. pneumoniae.
RESULTS
Susceptibility rates of optochin test for S. pneumoniae were as follows. Human blood containing media : 100% with the exception of MHA; sheep blood containing media : MHA; 100%, others; ranged from 98.3% to 94.8%. Among the 11 alpha-hemolytic streptococci, no isolate was susceptible to optochin in sheep blood TSA (3 mm depth) with streaking method, while the susceptibility rate by the other methods ranged from 9.1% to 36.4%.
CONCLUSIONS
Sheep blood containing TSA with streaking method is the most efficient method for the primary presumptive identification of S. pneumoniae because of its low false positivity and high sensitivity.