Detection of β-lactam resistance genes in Gram-negative bacteria from positive blood cultures using a microchip-based molecular assay.

Background: Accurate detection of β-lactam resistance genes in bloodstream infections is critical for guiding antimicrobial therapy. This study evaluates the Alifax Gram-negative resistance (GNR) microchip assay for detecting β-lactam resistance genes directly from positive blood cultures (PBCs) for Gram-negative (GN) bacteria, including Enterobacterales, , and .

Methods: Simulated (n=146) and clinical (n=106) GN-PBC samples were tested for , , , , -like, -like, -ESBL, group, and -like genes using the GNR microchip assay. Whole-genome sequencing (WGS) served as the reference assay for simulated samples and, selectively, for clinical samples. The bioMérieux BioFire Blood Culture Identification 2 (BCID2) panel assay was used as a comparator for clinical samples.

Results: The GNR microchip assay correctly identified 203 (99.5%) of 204 β-lactam resistance genes in simulated samples. One sample tested false negative for a -ESBL gene but true positive for a gene. In clinical samples, GNR results were concordant with BCID2 for 113 (100%) of 113 genes included in both assays. Additionally, the GNR assay detected bla -like (n=6), -like (n=5), and -ESBL (n=2), which are not targeted by BCID2, all confirmed by WGS. In two β-lactam-resistant samples but negative by the GNR assay, WGS confirmed the absence of acquired β-lactam resistance genes, suggesting alternative resistance mechanisms.

Conclusion: The GNR microchip assay demonstrated high concordance and broader β-lactam resistance gene coverage compared to BCID2, supporting its potential role in routine diagnostics. Further validation in larger, prospective studies is warranted.