Maldi biotyper smart system

The MBT STAR^®-Carba IVD kit (Bruker Daltonik) was tested according to the manufacturer’s instructions. Briefly one to five colonies from overnight cultures or the pellet obtained from positive blood cultures was mixed with the reconstituted MBT STAR^®-Carba Antibiotic Reagent containing imipenem (0.25 mg/mL). After incubation at 35°C under agitation for 30 min (60 min for Acinetobacter spp. and for blood culture derived samples), the reaction mixture was centrifuged and 1 μL of the supernatant was spotted in duplicate onto the MALDI target. Dried spots were overlaid with MBT STAR^®Matrix and were analyszed on the MALDI Biotyper smart system (Bruker Daltonik GmbH) with the MBT STAR^®-BL IVD module (Figure 1). This software provides an interpretation of the carbapenemase activity of each tested isolate based on the imipenem hydrolysis intensity compared with a negative and positive control strain, respectively, Escherichia coli ATCC 25922 and a characterized clinical KPC-producing Klebsiella pneumoniae (Figure 2). Discordant results between the assay and the molecular resistance gene identification led to repetition of both methods.

To confirm species-level identification, each strain within S. aureus complex underwent MALDI-TOF MS identification using the MALDI Biotyper SMART system (Bruker Daltonics, Bremen, Germany) with the MBT IVD Library DB-Revision G (10694 MSP). The ethanol formic acid extraction method was used for all 275 isolates. Species identifications with score >2.0 in the top 10 identification results were taken into consideration.