Controlled Clinical Laboratory Comparison of Two Supplemented Aerobic and Anaerobic Media Used in Automated Blood Culture Systems To Detect Bloodstream Infections

Abstract

A 20-ml blood sample was collected from adult patients with suspected bloodstream infections and distributed equally into the four volume-controlled bottles of a blood culture set consisting of aerobic and anaerobic BACTEC Plus/F bottles and aerobic and anaerobic BacT/Alert FAN bottles. All bottles were incubated in their respective instruments for a standard 5-day protocol or until the instruments signalled positivity. Samples in all bottles with negative results by these instruments were terminally subcultured. A total of 8,390 blood culture sets were obtained during the study period, of which 4,402 (52.5%) met the study criteria. Of these, 946 (21.5%) were positive either by instrument signal or by additional terminal subculture of all negative bottles and yielded growth of microorganisms. Five hundred eighty-nine (13.4%) blood culture sets were considered to have recovered 663 clinically significant organisms. When both the BACTEC and the BacT/Alert systems were used, 465 positive sets were detected; BACTEC alone detected 52 positive sets and BacT/Alert alone detected 72 (P = 0.09). No differences were found between the two systems in microbial recovery rate from blood cultures obtained from patients on antibiotic therapy. Significantly more members of the family Enterobacteriaceae (P < 0.01) were detected from patients without antimicrobial therapy by BacT/Alert than by BACTEC. The false-negative rates were 0.20% for BACTEC and 0.32% for BacT/Alert. A significantly higher false-positive rate was found for BACTEC (P < 0.0001). Both systems were comparable for the time to detection of microorganisms. However, gram-positive bacteria were detected faster by BACTEC andEnterobacteriaceae were detected faster on average by BacT/Alert. We concluded that both systems are comparable in their abilities to recover aerobic and anaerobic organisms from blood cultures and a terminal subculture might not be necessary for either of the two systems. The increased positivity rate when using an anaerobic bottle in a two-bottle blood culture set is due to the additional blood volume rather than to the use of an anaerobic medium.

Bacterial contamination of ex vivo processed PBPC products under clean room conditions

“…Many different blood culture systems are in use for the detection of microorganisms in human blood or body fluids. Others tested the blood culture systems used in our study and found comparable abilities of recovering aerobic and anaerobic organ‐isms 20‐22 . Therefore, we believe that the blood culture systems used in our study does not contribute to the differences in contamination rate.…”

“…Nevertheless, the volume of material inoculated in the blood culture bottles might influence the detection rate 20 . Weinstein and colleagues, 23 who performed a study to evaluate 5 versus 10 mL of blood cultured in aerobic BacT/Alert blood culture bottles, found a significant increase in the yield and speed of detection of blood pathogens 23 .…”

Failure of an Automated Blood Culture System To Detect Nonfermentative Gram-Negative Bacteria

“…Recently, in a comparative study between the BACTEC 9240 (Becton Dickinson, Heidelberg, Germany) and the BacT/ Alert system, Ziegler et al reported 9 versus 14 false-negative blood cultures, respectively (8). Although the overall falsenegative rate for the BacT/Alert was only 0.32% in that study, more than 64% of the false-negative cultures were P. aeruginosa, Acinetobacter spp., and S. maltophilia.…”

“…In response to these demands, the development of continuously monitoring blood culture systems took place. The BacT/ Alert system (Organon Teknika, Eppelheim, Germany) is one of the fully automated blood culture systems (8). The BacT/ Alert software examines the readings from each bottle to determine if there is evidence for bacterial growth.…”

“…The detection system accomplishes this by using three types of measurements of the CO 2 level: (i) the present CO 2 level in the bottle, (ii) the rate of CO 2 production, and (iii) the acceleration of this rate. The combination of the three measurements allows the system a high degree of accuracy and specificity (8).…”