Evaluation of the AID AmpC line probe assay for molecular detection of AmpC producing Enterobacterales

Abstract Objectives In this study, the commercially available AID AmpC line probe assay (LPA) was evaluated for detection of plasmid-mediatedblaAmpC β-lactamase genes in Enterobacterales as well as chromosomal mutations in the blaAmpC promoter/attenuator regions in Escherichia coli. Methods Accuracy of the AID AmpC probes was assessed using Enterobacterales clinical isolates harbouring diverse plasmid-mediated AmpC enzymes (ACC, ACT, DHA, FOX, CMY and MOX) and E. coli clinical isolates with mutations in the chromosomal blaAmpC promoter/attenuator regions. The diagnostic performance of the AID AmpC LPA for blaAmpC detection directly from clinical specimens was determined using 99 clinical urine specimens with bacterial cell counts >105 CFU/mL and the results were compared with culture-based phenotypic drug susceptibility testing (DST). Results Detection of blaAmpC genes in Enterobacterales clinical isolates showed 100% congruence with phenotypic DST results. The AID AmpC LPA showed 100% specificity [95% confidence interval (CI) 96–100%] and 100% sensitivity (95% CI 75–100%) for detection of plasmid-meditated blaAmpC and E. coli genomic blaAmpC promoter/attenuator mutations directly from clinical urine specimens. The AID AmpC LPA detected three AmpC-producers in urine specimens with bacterial cell counts >105 CFU/mL that were missed by culture-based phenotypic DST, thereby displaying higher diagnostic sensitivity. Conclusion The AID AmpC LPA is an accurate, sensitive and easy-to-use test that can be readily implemented in any diagnostic laboratory for molecular detection of blaAmpC genes in Enterobacterales.