Processing of Positive Blood Cultures Using a Total Laboratory Automation System: Workflow and Clinical Validation
Authors: Mitchell Kaitlin , Crozier Abby , Burnham Carey-Ann , Yarbrough Melanie 
Published: September 2019

Automated systems for culture-based microbiology are in the early phase of implementation in clinical laboratories. Here, our objective was to evaluate the performance of the BD Kiestra Total Laboratory Automation (TLA) System for inoculation, incubation, and imaging of positive blood culture broth specimens. To optimize parameters for clinical testing, 56 clinical specimens were processed using both TLA and manual standard-of-care (SOC) methods. For TLA processing, 3 mL positive blood culture broth (35 VersaTREK: 19 aerobic, 16 anaerobic; 21 BD BACTEC: 15 aerobic, 6 anaerobic) was transferred to a no-additive vacutainer using a safety adapter and syringe. This aliquot was then placed on TLA for fully automated processing: 10 µL was inoculated to blood, chocolate, and MacConkey agar (Remel) and, for anaerobic bottles only, Brucella blood agar (Hardy Diagnostics). Kiestra cross-streak pattern 5 was optimal for obtaining isolated colonies and was superior to quadrant-streaking methods. Additional media types were added based on Gram stain results of the positive blood specimen: CandiSelect (Bio-Rad) and Sabouraud Dextrose (Remel) were added if yeast were identified, and Colistin Nalidixic Acid agar (Remel) for Gram stains with mixed Gram-positive and Gram-negative morphology. Plates were imaged at 6, 8, 10, 12, 18, 38, and 62 hours. Anaerobic media were placed by the system in a media stacker, incubated off-line, and then imaged on the TLA at 24, 48, and 72 hours. SOC cultures were evaluated after overnight incubation and on days 2 and 3. Organism identification was performed using MALDI-TOF MS (Bruker). Based on our evaluation, optimal parameters for clinical implementation of TLA were identified. Microbial growth was scant at 6 hours of incubation, but by 8 hours, small discrete colonies were observed for most aerobes. Thus, imaging parameters selected for routine clinical testing were 8, 18, and 38 hours for aerobic media and one image taken at 38 hours for anaerobic media. TLA and SOC culture results had 96% agreement (29 Gram positive, 12 Gram negative, 5 mixed, 6 yeast, 1 no growth). Two specimens with a second low-abundance bacterial population were observed on TLA that were not observed with SOC. Reproducibility of TLA was tested by processing 6 positive samples in triplicate and found to be 100%. There was no carryover or contamination noted between specimens processed simultaneously on TLA. To evaluate if implementation of TLA impacted epidemiology of positive blood cultures, we compared the 10 most common organisms recovered pre- and post-TLA implementation (August-November 2017 compared to August-November 2018). We found these organisms were not significantly impacted by TLA processing. In conclusion, automated processing of positive blood cultures improves laboratory workflows and facilitates faster workup at 8 hours of incubation. These results demonstrate that automation is a viable avenue for the processing of positive blood cultures.