In vitro Evaluation of BACT/ALERT® VIRTUO®, BACT/ALERT 3D®, and BACTEC™ FX Automated Blood Culture Systems for Detection of Microbial Pathogens Using Simulated Human Blood Samples

Abstract

Blood culture (BC) is still the standard for diagnosing bloodstream infections (BSIs), especially those caused by bacteria and fungi. Infection-complicating sepsis or septic shock often occurs at BSI onset, making necessary to improve the diagnostic yield of positive BCs. Among the BC systems currently available, the BACT/ALERT® VIRTUO® (VIRTUO) system has been developed to shorten time to detection (TTD) of positive BCs. In this study, we assessed TTD for 330 clinically relevant species including 14 Gram-positive, 14 Gram-negative, and 5 yeast isolates in spiked human blood samples that were tested in parallel with VIRTUO BACT/ALERT® 3D (BTA3D) and BACTEC™ FX (BACTEC) systems. We inoculated 30 colony-forming unit (CFU) from each microbial suspension into BACT/ALERT® Plus or BACTEC™ Plus (aerobic/anaerobic or pediatric) BC bottles, and we used two different blood volumes to simulate, respectively, the BCs collected from adult and pediatric patients. Of 2,610 bottles tested, 2,600 (99.6%) signaled positive in the three systems. Only the BACTEC system did not detect Staphylococcus lugdunensis isolates in anaerobic bottles. Among adult simulated cultures, the median TTD was significantly shorter for aerobic/anaerobic bottles incubated in VIRTUO (11.6 h and 10.1 h) compared to bottles incubated in either BTA3D (13.3 and 12.3 h) or BACTEC (13.5 and 12.2 h) system. Among pediatric simulated cultures, the median TTD was significantly shorter for bottles incubated in VIRTUO (11.2 h) compared to bottles incubated in either the BTA3D (13.0 h) or BACTEC (12.5 h) system. Compared to BTA3D and/or BACTEC systems, VIRTUO allowed faster growth detection for most of the 33 microbial species tested. Notable examples were Salmonella spp. (7.4 h by VIRTUO vs. 10.1 h and 9.2 h by either BTA3D or BACTEC) and Streptococcus agalactiae (8.1 h by VIRTUO vs. 10.3 and 9.4 h by either BTA3D or BACTEC). The few notable exceptions included Stenotrophomonas maltophilia and some Candida species. Together, these findings confirm that VIRTUO has greater potential of improving the laboratory detection of bacteremia and fungemia than the progenitor BTA3D or the competitor BACTEC system.

Recovery of Gram-Negative Bacteria from Aerobic Blood Culture Bottles Containing Antibiotic Binding Resins after Exposure to β-Lactam and Fluoroquinolone Concentrations

“…TTD was also compared between the BacT/Alert and Bactec bottles in their respective systems. For all isolates tested in the absence of any antibiotic concentrations (i.e., control bottles), TTD was faster for the BacT/Alert bottles in the Virtuo system, which is consistent with previous studies (21). These observations carried over to the antibioticcontaining bottles, where TTD was significantly shorter for BacT/Alert bottles when inoculated with E. coli and K. pneumoniae.…”

Efficient Inactivation of Clinically Relevant Antimicrobial Drug Concentrations by BacT/Alert or Bactec Resin-Containing Media in Simulated Adult Blood Cultures

“…Before testing, the bacterial strains were subcultured twice overnight on standard solid media at 37°C, and their MICs were determined with the broth microdilution method according to the ISO 20776-1/2006 procedure as recommended by EUCAST (18). In our BC simulation model (19), each bottle was spiked with 8-ml banked whole blood (obtained from the Division of Transfusion Medicine at our institution), 0.5-ml antibiotic solution (obtained as described above), and 0.5-ml bacterial suspension (50 to 100 CFU, achieved after diluting a suspension of ϳ5 ϫ 10 8 CFU/ml in phosphate-buffered saline). Resins are equally useful in the presence of lower and higher microbe quantities, as those present in blood during BSIs (20), but we decided on a more stringent experimental approach and used only one inoculum in the study.…”

Modern Blood Culture

“…Although all 3 systems flagged positive for 99.6% of all cultures, the median time to positivity for the BacT/ALERT VIRTUO was significant shorter. 28 A previous study comparing the BacT/ALERT 3D and VersaTREK using patient specimens found no overall difference in time to positivity or isolation of microorganisms, but there was a higher false-positive rate with the VersaTREK system (ie, 1.6% vs 0.7% for aerobic bottles). 29 However, the VersaTREK demonstrated a statistically significant higher recovery of streptococci and enterococci.…”