Direct Comparison of the BACTEC 9240 and BacT/ALERT 3D Automated Blood Culture Systems for Candida Growth Detection

A direct comparison of two automated blood culture systems was conducted to compare their ability to detect Candida growth. The systems evaluated were the BACTEC 9240 (Bactec) and BacT/ALERT 3D (BacT). The aerobic, anaerobic, and mycology media for each system were evaluated: Bactec Plus Aerobic/F, Plus Anaerobic/F, and Myco/F Lytic bottles, respectively, and BacT FA, SN, and MB bottles, respectively. Each blood culture bottle was inoculated with fresh blood from healthy donors. Fifty isolates of Candida spp. were used. The six different blood culture bottles were each inoculated with 1,000 yeasts per bottle and then incubated in the corresponding automated system. The BacT detected growth of 90% (135 of 150) of Candida pathogens, while Bactec detected 66% (100 of 150). Growth was detected in all BacT and Bactec mycology bottles, all BacT aerobic bottles, and by terminal subculture of all bottles. Sixty-five of 300 (22%) bottles had no growth detected; 50 from the Bactec (5 aerobic and 45 anaerobic) and 15 from the BacT (all anaerobic). Terminal subculture of "negative" bottles demonstrated viable yeast growth from all 65 bottles, representing 65 false-negatives. The mean time to growth detection in the BacT system was 25.62 h while the Bactec was 27.30 h (P < 0.01). Both automated blood culture systems detected all episodes of simulated candidemia when specialized mycology media were used. However, when only standard aerobic and anaerobic media were used, the BacT performed better than the Bactec in overall growth detection, time to growth detection, and number of false-negatives.