Table 3.
Isolation of optochin-sensitive pneumococcal colonies (number of optochin-sensitive/number of colonies selected), using the standard dilution method compared with the MBS method
| Number of 19A colonies identified in Saliva A | Number of 19A colonies identified in Saliva B | |||
|---|---|---|---|---|
| CFU/mL of S. pneumoniae 19A | Saliva A with MBS method | Saliva B with standard dilution method | Saliva A with MBS method | Saliva B with standard dilution method |
| 5×104 | 15/16 | 15/16 | 15/16 | 1/16 |
| 5×103 | 15/16 | 5/16 | 5/16 | 0/16 |
| 5×102 | 16/16 | 2/16 | 0/16 | 0/16 |
| 5×101 | 6/24 | 0/24 | 0/24 | 0/24 |
Two pneumococcal-negative saliva samples (A and B) were spiked with four concentrations of serotype 19A. Pure pneumococcal colonies were identified by a zone of inhibition around the optochin disk, and any colonies that were mixed colonies (i.e., those with a zone of inhibition but some secondary growth [a non-pneumococcal contaminant] growing within the zone of inhibition or had satellite colonies appearing withing the zone of inhibition) were considered to be successful isolation of pneumococcus.