MALDI biotyper-based rapid resistance detection by stable-isotope labeling.

Against the background of increasing numbers of resistant microorganisms, the fast and cost-efficient detection of microbial resistance is an important clinical requirement for optimal therapeutic intervention. Current routine assays take at least 5 h, but in most cases an overnight incubation is necessary to identify resistant isolates. The usage of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) profiling in combination with growth media containing isotopically labeled amino acids facilitates the detection of resistant microorganisms after 3 h or less directly from the profile spectrum. Growing microorganisms incorporate isotopically labeled amino acids, increasing protein masses and thereby leading to mass shifts of their corresponding peaks in the profile spectra. In the presence of antibiotics, only resistant microorganisms are able to grow and to incorporate the labeled amino acids. This leads to a difference in the mass spectra of susceptible and resistant isolates, allowing their differentiation. In the presented study, we demonstrated the applicability of this novel approach for the detection of methicillin-resistant Staphylococcus aureus and tested different bioinformatics approaches for automated data interpretation.