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

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.

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.

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.

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.

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.