Comparison of the two blood culture systems, Bactec 9240 and BacT/Alert 3D, in the detection of Candida spp. and bacteria with polymicrobial sepsis

The purpose of this investigation was to evaluate the performance of the Bactec 9240 and BacT/Alert 3D blood culture systems in the detection of Candida spp. and bacteria in simulated polymicrobial sepsis models. A total of 28 clinical isolates of Escherichia coli, Staphylococcus aureus, Candida albicans, and Candida glabrata were studied. Five polymicrobial models of C. albicans + S. aureus, C. albicans + E. coli, C. glabrata + S. aureus, C. glabrata + E. coli, and C. albicans + C. glabrata were prepared. Each combination was inoculated in five different blood culture vials. The two systems were compared for culture positivity and time to detection (TTD). Twenty-four mixed cultures with a yeast and a bacteria were tested. Bactec Mycosis vials could detect yeasts in all 24 cultures. The aerobic vials from both Bactec and BacT/Alert could detect both yeasts and bacteria in 22/24 (91.66 %) cultures. Bactec Plus Anaerobic/F and BacT/Alert FN vials could detect both microorganisms in 19/24 (79.16 %) and 4/24 (16.67 %) vials, respectively. Seven polymicrobial sepsis models with C. albicans + C. glabrata were also tested. Mycosis vials could detect both yeasts in 7/7 mixed cultures. The aerobic vials from Bactec and BacT/Alert could detect both yeasts in 3/7 and 2/7 mixed cultures, respectively. Bactec Plus Aerobic/F had a shorter TTD compared to BacT/Alert FA and Bactec Plus Anaerobic/F vials (p < 0.0001 and p < 0.01, respectively). The present study shows that the Bactec and BacT/Alert systems have different characteristics in the detection of yeasts and bacteria with polymicrobial sepsis.