Biphasic Versus Monophasic Manual Blood Culture Bottles for Low-Resource Settings: An In-Depth <i>in vitro</i> Evaluation Using Simulated Blood Cultures

Abstract

Introduction: Manual (visually read) blood culture bottles (BCB) are frequently used in low-resource settings (LRS) where automated alternatives are less suitable. Yet performance evaluations of these BCBs are lacking, especially in comparison to automated systems. We evaluated two manual BCB types (the Bi-State BCB, Autobio; visually read BacT/ALERT bottles, bioMerieux) and used BacT/ALERT BCB monitored in a BacT/ALERT automate as a reference method. Methods: BCBs were spiked in triplicate with 177 clinical isolates representing pathogens frequently found in LRS (19 bacterial, 1 yeast species) for both adult and pediatric formulations. Growth in manual BCBs was evaluated by visually inspecting the broth, agar slant, and – for BacT/ALERT BCB – color change of the growth indicator. Blind subculture was conducted after overnight incubation (Day 1). Results: Overall yield was 95·9% and 95·5% for Bi-State and manual BacT/ALERT respectively, versus 96·1% for the reference method. The lowest yield occurred for Neisseria meningitidis and Burkholderia cepacia (83·3% and 83·1%) and was consistent among the three BC systems. On Day 1, growth was detected in 90·7% and 75·0% of grown BCBs in Bi-State and BacT/ALERT respectively, versus 99·3% for the reference method. On Day 2 detection rates were 100%, 97·7% and 100% respectively. Among 1013 grown Bi-State BCBs, growth mostly co-occurred in broth and slant (81·7%). Sufficient colony growth on the slant to perform further tests was present in only 44·1% and 59·0% of biphasic bottles on Day 2 and Day 3 respectively. Blind subculture generated colonies on Day 2 for 99·7% grown Bi-State and 99·2% of manual BacT/ALERT bottles respectively. Conclusion: In these in-vitro experiments, the yield and time-to-detection of manual BCBs were comparable to an automated system. Bi-State BCBs outperformed manual BacT/ALERT bottles, but the agar slant did not allow earlier detection nor earlier colony growth when compared to blind subculture on Day 1. Funding Statement: This research was funded by Medecins Sans Frontieres (Mini-Lab project). Medecins Sans Frontieres participated in study design, interpretation and writing of the manuscript. Declaration of Interests: None to declare. Ethics Approval Statement: Leftover blood from blood bank volunteers was used under research contract (file number CM20180327A). Clinical strains were obtained from ITM travel clinic and microbiological surveillance studies (Surveillance of antimicrobial resistance among consecutive blood culture isolates in tropical settings, Institutional Review Board 613/08, Ethical Committee University Hospital of Antwerp 8/20/96).