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

Objectives: Development of a novel MALDI-TOF MS-based method for the rapid detection of ESBL-producing Enterobacteriaceae. Methods: 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. Results: 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. Conclusions: 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.