Amperometric detection of extended-spectrum beta-lactamase activity: application to the characterization of resistant E. coli strains

The amperometric detection of extended-spectrum beta-lactamase (ESBL) with carbon screen-printed sensors was investigated in the presence of the Nitrocefin, a commercially-available beta-lactamase chromogenic cephalosporin substrate. Using an ESBL isolated from a clinical sample, it was shown for the first time that the intensity of a specific anodic pic current (E-P = similar to+ 0.3 V vs. Ag/AgCl) resulting from the catalytic hydrolysis of the beta-lactam ring was proportional to the amount of ESBL. The proof-of-principle of a novel susceptibility assay for the rapid and accurate identification of ESBL-producing bacteria was then demonstrated. The detection scheme relied on (i) the culture of the sample in a medium containing the cefotaxime supplemented or not with the clavulanic acid inhibitor to allow the specific determination of ESBL producers (ii) followed by the incubation of the bacteria with the Nitrocefin and (iii) the measurement of the enzyme product by cyclic voltammetry. The amperometric assay was further applied to the characterization of E. coli strains and to the quantification of the ESBL producers. A detection limit of 5 x 10(4) cfu mL(-1) ESBL-producing E. coli was achieved after a 10 min incubation time. In contrast to the approved routine assays, the electrochemical approach, which did not require isolated colonies to be performed, provided quantified results regarding ESBL activity within a few hours. Finally, owing to its cost-effectiveness, portability and simplicity, this test holds great promise for clinical and environmental applications.