Comparison of media and culture techniques for detection of Streptococcus pneumoniae in respiratory secretions.

We compared the relative efficacy of three methods for the isolation of Streptococcus pneumoniae in lower respiratory secretions. Based on results from 294 clinical specimens, we found that S. pneumoniae was isolated at a frequency of 65% with 5% sheep blood agar or 5% sheep blood agar containing 5 micrograms of gentamicin per ml, both incubated in 5% CO2. Anaerobic incubation of 5% sheep blood agar enhanced the recovery rate of S. pneumoniae to 93%. The improved efficacy with anaerobic incubation is due to the greater ease of recognition of the larger and more mucoid colonies of S. pneumoniae, and to the suppression of the growth of other oral bacteria present in the respiratory sections.