Towards the early detection of β-lactamase-producing Enterobacteriaceae by MALDI-TOF MS analysis

Development of a novel MALDI-TOF MS-based method for the rapid detection of ESBL-producing Enterobacteriaceae.

The method was evaluated in terms of sensitivity, specificity and turnaround time regarding the antibiotic used (cefotaxime, ceftazidime, ceftriaxone, cefpodoxime or cefepime) and the performance of the automated MBT STAR-BL software (Bruker Daltonik GmbH, Germany) relative to qualitative interpretation of spectra for detecting β-lactamase resistance by MALDI-TOF MS (Bruker Daltonik) in a collection of 11 isogenic Escherichia coli control strains expressing different β-lactamases. Finally, for clinical validation, β-lactamase activity was determined under previously evaluated conditions in 100 clinical isolates previously characterized by PCR and sequencing.

Clinical validation of the assay showed 100% sensitivity and specificity for detecting β-lactam resistance in 30 min by measuring hydrolysis of ceftriaxone (0.50 mg/mL) with the automated MBT STAR-BL software. Regarding the antibiotics evaluated, ceftriaxone yielded 70% more positive results than cefotaxime, 80% more than ceftazidime and 20% more than cefpodoxime, with 100% specificity. Cefepime revealed 100% sensitivity, but only 27% specificity. For the same incubation time, the automated software yielded on average 41% more positive results in relation to detecting resistance than qualitative interpretation of spectra.

Our clinical validation of the method proved it to be highly reliable, simple to perform and time saving, transforming β-lactam resistance detection by MALDI-TOF MS into a ready-to-use technique in clinical laboratories.