Diagnostic accuracy of short-incubation cultures versus standard protocols for bacterial identification and susceptibility testing via VITEK® MS and VITEK®2 XL

Sepsis is a medical emergency associated with high morbidity and mortality rates. Rapid pathogen identification and early antimicrobial susceptibility results are essential for optimizing treatment. Conventional protocols require at least 24 h, delaying clinical decision-making. This study evaluated the accuracy and feasibility of a short-incubation protocol compared to the traditional method.

This diagnostic accuracy study included positive monomicrobial blood cultures from patients across all age groups. The index test used biomass collected after a 6-h incubation on solid media, whereas the reference standard employed the conventional 24-h protocol. Outcomes assessed were agreement in bacterial identification by MALDI-TOF MS, detection of resistance mechanisms, and categorical agreement in antimicrobial susceptibility profiles (AST) using the VITEK® 2 XL system. Diagnostic performance was determined by overall agreement, Cohen's kappa (κ), sensitivity, and predictive values.

154 monomicrobial blood cultures were analyzed. For bacterial identification, the short-incubation protocol demonstrated overall agreement (κ = 0.99; 95% CI: 0.96-1.00), with only one discordant result. For AST, overall agreement reached 96.5% (κ = 0.91). While the highest concordance was observed for common Enterobacterales such as Escherichia coli and Klebsiella pneumoniae, discrepancies were noted for specific drug-organism pairs, particularly among Gram-positive cocci and for certain beta-lactams.

The 6-h short-incubation protocol represents a robust alternative for rapid pathogen identification via MALDI-TOF MS, reducing diagnostic turnaround time by up to 18 h. However, the observed variability in AST for critical combinations suggests that clinical implementation must be stratified and selective, prioritizing patient safety over reporting speed.