Performance of a novel fluorogenic chimeric analog for the detection of third-generation cephalosporin resistant bacteria

Resistance to third generation cephalosporins is widely disseminated in Enterobacteriaceae mainly due to extended-spectrum-β-lactamases, plasmid AmpC β-lactamases, and hyperproduction of chromosomal AmpC β-lactamases. Here we evaluated the performance of a novel fluorogenic probe rapid test and compared the results with the phenol red assay using a total of 77 characterized organisms (44 extended-spectrum-β-lactamases, 33 chromosomal or plasmid AmpC β-lactamases) and 46 susceptible organisms. The fluorescent assay showed higher sensitivity than the phenol red assay in cefotaximase type extended-spectrum-β-lactamases, non- cefotaximase type extended-spectrum-β-lactamases, chromosomal AmpC β-lactamases, and plasmid AmpC β-lactamases (96.7% vs. 90.0%, p=0.157; 71.4% vs. 7.1%, p=0.003; 100.0% vs. 64.7%, p<0.001; 100.0% vs. 6.3%, p<0.001). The fluorescent assay had a positive correlation with the exponents of cefotaxime and ceftazidime minimum inhibitory concentrations (p<0.001 for both). The new fluorescent assay will be very useful for the rapid detection of resistance to third generation cephalosporins that originates from various β-lactamases.