Effect of agitation and frequent subculturing on recovery of aerobic and facultative pathogens by Roche Septi-Chek and BACTEC blood culture systems

Abstract

The positivity rate and time to recovery of pathogens were compared in Roche Septi-Chek (RSC-TSB) and BACTEC radiometric systems on 3,539 paired blood cultures. Both systems were steadily agitated, with frequent subculturing or processing of the RSC-TSB agar slides and BACTEC bottles, respectively, during the first 24 h of incubation. The RSC-TSB system recovered 249 pathogens (7.0% positivity rate), compared with 234 (6.6% positivity rate) isolates recovered from BACTEC. For the most common isolates, Staphylococcus aureus and the Enterobacteriaceae, the median time to detection was 15.8 h for BACTEC and 18.6 h for the RSC-TSB system. No statistically significant difference was observed in recovery of organisms from the two systems, except for S. aureus (P less than 0.05). In the RSC-TSB system, 42% of S. aureus, 58% of the Enterobacteriaceae, and 45% of Pseudomonas aeruginosa isolates had sufficient growth on the agar slant to allow performance of rapid standardized identification and susceptibility studies. In comparison with other studies using static incubation, it appears that agitation and frequent subculturing of the RSC-TSB system during the first 24 h of incubation decreased the time to detection for the majority of significant blood culture isolates.