TABLE 1.

Principal assays to determine resistance or susceptibility of microbes by mass spectral techniques.

Assay principle	R/S	Technique	Targeted resistance mechanism	Targeted taxa and prerequisites
Identification of resistant phylogroups	R	WCMS	taxon-specific	Selected taxa for which molecular reference data are available
Direct detection of proteins conferring resistance	R	MALDI MS LC-MS	General, but with largely technical limitations	General, but protein sequences have to be known
Detection of biomarkers associated with antibiotic resistance	R	MALDI MS	Specific for selected mechanisms	Individual taxa, preferably with sufficient genomic or PCR data
Monitoring antibiotic degradation	R	MALDI MS LC-MS	Lactamases (carbapenemases)	Possibly general; explored mostly for Enterobacteriaceae, Pseudomonas, Acinetobacter
Detection of microbial growth	S	MALDI MS	General	General for taxa growing in homogeneous suspension

In column R/S it is indicated whether resistance (R) or susceptibility (S) is determined.