Comparison of growth performance of the BacT/ALERT VIRTUO and BACTEC FX blood culture systems under simulated bloodstream infection conditions

Background: We evaluated growth performance of the BacT/ALERT VIRTUO and the BACTEC FX blood culture (BC) systems based on recovery rate and time to detect microorganisms under simulated bloodstream infection conditions. Methods: Three expected concentrations of 125,30, and 5 CFU/mL of eighteen reference microorganisms were diluted with 5 mL blood for adult aerobic/anaerobic culture and with 3 mL for pediatric aerobic culture and inoculated, and each of three BC bottles were loaded into the two BC systems. Results: A total of 405 comparative bottles were analyzed in this study. The percent agreement between the BacT/ALERT VIRTUO and BACTEC FX systems after comparing the positive results was 96.8% (392/405). The BacT/ALERT VIRTUO and BACTEC FX systems yielded 100% positive signals at 125 and 30 CFU/mL, whereas there were 5.2% (7/135) and 8.1% (11/135) false-negative results at 5 CFU/mL, respectively. No statistical difference in recovery rate based on the overall concentration of microorganisms was observed between the two BC systems (p = 0.329). No statistical difference in time to detection (TTD) was observed between the two BC systems based on the overall concentration of microorganisms (p = 0.067). Inter-instrument comparisons of TTD resulted in a good correlation (r = 0.947) for all inoculated bottles. Conclusions: The BacT/ALERT VIRTUO showed similar recovery rate and TTD of microorganisms, compared to BACTEC FX BC system. Due to its versatility to accommodate a higher workload through automated loading and unloading of BC bottles with faster detection of pathogens from bloodstream, the BacT/ALERT VIRTUO system may establish itself as a useful alternative.