Development of multiplex Luminex assays for the surveillance of antimicrobial resistance genes in nasal samples.

Bovine respiratory disease (BRD) is the major cause of morbidity and mortality in feedlot cattle. It is the major driver for the therapeutic use of antimicrobials in feedlot cattle with their continued use and effectiveness being underpinned through the implementation of stewardship programs that include monitoring of resistance levels. To enable these programs, rapid and user-friendly assays are needed to detect antimicrobial resistance genes (ARG) for efficient monitoring. This study developed multiplex Luminex assays targeting 34 ARGs and validated them using reference strains of Pasteurellaceae and other bacteria, as well as field samples from nasal swabs of cattle (n = 94) undergoing BRD treatment at an Australian feedlot. One swab was collected from each nostril of every animal, with one being used for bacterial culture and conventional PCR analyses for ARGs, while the DNA extracted from the second swab was analyzed using the novel Luminex assays for the presence or absence of the ARGs of interest. The pathogens isolated by culture were tested for macrolide resistance genes erm(42), mph(E) and msr(E); sulfonamide resistance genes, sul1 and sul2; florfenicol resistance gene floR; β-lactam resistance gene blaRob-1 and tetracycline resistance genes tet(Q) and tet(Y), by conventional PCR. Kappa statistics suggested a moderate agreement between the tests in detecting the macrolide resistance genes. Luminex based analyses identified more resistance genes than PCR on cultured organisms, revealing the presence of a broader array of these genes than previously reported. In addition to detecting more genes, Luminex assays could process a higher number of samples in a single day, making them well-suited for ongoing surveillance of antimicrobial resistance in BRD affected cattle. This capability is essential for optimising therapeutic use and detecting emerging resistance patterns.