Performance of Two Resin-Containing Blood Culture Media in Detection of Bloodstream Infections and in Direct Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry (MALDI-TOF MS) Broth Assays for Isolate Identification: Clinical Comparison of the BacT/Alert Plus and Bactec Plus Systems

Abstract

We compared the clinical performances of the BacT/Alert Plus (bioMérieux) and Bactec Plus (Becton Dickinson) aerobic and anaerobic blood culture (BC) media with adsorbent polymeric beads. Patients >16 years old with suspected bloodstream infections (BSIs) were enrolled in intensive care units and infectious disease wards. A single 40-ml blood sample was collected from each and used to inoculate (10 ml/bottle) one set of BacT/Alert Plus cultures and one set of Bactec Plus cultures, each set consisting of one aerobic and one anaerobic bottle. Cultures were incubated <5 days in the BacT/Alert 3D and Bactec FX instruments, respectively. A total of 128 unique BSI episodes were identified based on the recovery of clinically significant growth in 212 aerobic cultures (106 BacT/Alert and 106 Bactec) and 151 anaerobic cultures (82 BacT/Alert and 69 Bactec). The BacT/Alert aerobic medium had higher recovery rates for Gram-positive cocci (P ‫؍‬ 0.024), whereas the Bactec aerobic medium was superior for recovery of Gram-negative bacilli (P ‫؍‬ 0.006). BacT/Alert anaerobic medium recovery rates exceeded those of the Bactec anaerobic medium for total organisms (P ‫؍‬ 0.003), Gram-positive cocci (P ‫؍‬ 0.013), and Escherichia coli (P ‫؍‬ 0.030). In terms of capacity for diagnosing the 128 septic episodes, the BacT/Alert and Bactec sets were comparable, although the former sets diagnosed more BSIs caused by Gram-positive cocci (P ‫؍‬ 0.008). They also allowed earlier identification of coagulase-negative staphylococcal growth (mean, 2.8 h; P ‫؍‬ 0.003) and growth in samples from patients not on antimicrobial therapy that yielded positive results (mean, 1.3 h; P < 0.001). Similarly high percentages of microorganisms in BacT/Alert and Bactec cultures (93.8% and 93.3%, respectively) were identified by direct matrix-assisted laser desorption ionization-time of flight mass spectrometry assay of BC broths. The BacT/Alert Plus media line appears to be a reliable, timesaving tool for routine detection of BSIs in the population we studied, although further studies are needed to evaluate their performance in other settings.

Optimized Use of the MALDI BioTyper System and the FilmArray BCID Panel for Direct Identification of Microbial Pathogens from Positive Blood Cultures

“…All consecutive positive BC bottles representing clinically significant BSI episodes (defined a posteriori as the isolation of bacteria and/or yeasts from the blood in the presence of signs and/or symptoms of infection and/or the isolation of at least one organism that was considered clinically relevant by the treating physician with the support of an infectious disease consultant [25,26]) were included in the final evaluation of our MALDI BioTyper/FilmArray BCID panel-based diagnostic algorithm. Cultures growing commensal organisms, such as coagulase-negative staphylococcus (CoNS) and viridans streptococcus, were judged to be clinically relevant when these organisms were recovered from Ͼ2 BCs in patients with clinical manifestations of infection that were not explained by other causes (15). BSI episodes separated by Ͼ1 week were considered to represent different episodes per patient.…”

“…Aliquots from each positive BC bottle/broth were subjected to routine Gram staining microscopy and solid-medium subcultures. After isolation from the cultures, bacteria and yeasts were identified by MALDI BioTyper analysis; in cases in which the isolate could not be identified (i.e., ID score was Ͻ2.0), conventional phenotypical tests and/or sequencing of the 16S rRNA gene or the rpoB gene (for bacterial isolates) and the internal transcribed spacer 1 (ITS1)-5.8S-ITS2 rRNA gene region (for fungal isolates) were performed as previously described (11,15,27). Antimicrobial susceptibility testing of the bacterial isolates was performed as part of the routine BC analyses with the Vitek 2 (bioMérieux) and/or Etest (bioMérieux), and interpreted according to EUCAST guidelines.…”

“…MALDI-TOF MS assays were performed starting from 8-ml BC aliquots, as previously described (11,15). Briefly, pellets containing bacterial or yeast cells were washed and then suspended in distilled water plus absolute ethanol.…”

“…The direct assays were performed several times daily on weekdays (from 7:30 a.m. to 7:00 p.m., Monday through Saturday). Blood cultures that arrived when the laboratory was closed were stored at room temperature, as previously described (15). All consecutive positive BC bottles representing clinically significant BSI episodes (defined a posteriori as the isolation of bacteria and/or yeasts from the blood in the presence of signs and/or symptoms of infection and/or the isolation of at least one organism that was considered clinically relevant by the treating physician with the support of an infectious disease consultant [25,26]) were included in the final evaluation of our MALDI BioTyper/FilmArray BCID panel-based diagnostic algorithm.…”

“…However, despite its well-documented good performance (8)(9)(10)(11)(12)(13)(14)(15)(16)(17), this method often fails to identify polymicrobial BCs in their entirety.…”