Modification of the rapid antimicrobial susceptibility testing from blood culture protocol for a resource-limited setting

Abstract

Background: Sepsis is a medical emergency and rapid antimicrobial susceptibility testing (RAST) is essential for patient management. However, existing RAST protocols may be unsuitable for resource-limited settings due to the need for rapid species identification, which may require specialized equipment or expensive reagents. Aims: To minimize the requirement of the RAST protocol while maintaining its efficacy, focusing on Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii and Staphylococcus aureus. Methods: Positive blood cultures suspected of having these pathogens underwent RAST with three main modifications: delayed species identification, implementation of pan-species breakpoints and the change in the quality control process. Twelve antimicrobials were tested for Gram-negative bacilli, and three for S. aureus. Species identification was performed by both the MALDI-TOF MS and the rapid phenotypic tests at the final RAST time point. The categorical agreement was evaluated against the standard AST method and the RAST protocol. Results: Among 398 samples, gentamicin, ampicillin, meropenem and trimethoprim-sulfamethoxazole met the accuracy criteria for Gram-negative bacilli. Ceftriaxone, imipenem and ciprofloxacin had slightly reduced agreement (80%–90%) due to a high false resistance. The remaining antimicrobials either had a low agreement or high false susceptibility. Only gentamicin passed the agreement criteria for S. aureus. The use of pan-species breakpoints resulted in several failed results without improvement in the concordance. The quality control process with and without sheep blood yielded comparable results. Conclusion: RAST reduced the time-to-result for key antimicrobial agents for at least 24 h while requiring minimal workflow disruption, enabling early adjustment of antimicrobial treatment.