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

•Rapid detection of resistance to third generation cephalosporins due to β-lactamases•Novel fluorescent probe for detecting hydrolysis of cefotaxime and ceftazidime•Performance of novel fluorescent assay and comparison with other rapid test, phenol red assay

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.