Rapid antimicrobial susceptibility testing by matrix-assisted laser desorption ionization-time of flight mass spectrometry using a qualitative method in Acinetobacter baumannii complex

The transmission and infections of multidrug-resistant bacteria can be prevented by rapid identification and antibiotic susceptibility testing (AST) for pathogenic bacteria in a clinical microbiology laboratory. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has been routinely used as a tool for the identification of pathogens; however, a simple and accurate method for a rapid determination of the antimicrobial susceptibility profile is an urgent requisite. The present study established a method based on mass spectrometry to determine the drug resistance. Acinetobacter baumannii complex isolates were tested as an example. After short-term culture, the isolates were incubated with meropenem of different concentrations to determine the growth or the inhibition of the growth by MALDI-TOF MS. The agreement of minimum inhibitory concentration (MIC) values between MALDI-TOF MS-based rapid AST and broth microdilution method in susceptible and resistant strains was 77.1% and 70.1%, respectively. The susceptibility-breakpoint concentration (2 μg/mL) achieved a 98.9% sensitivity and 100% specificity with respect to resistance detection. Similarly, 96.9% sensitivity and 100% specificity were obtained for resistance detection with meropenem concentration at 8 μg/mL. MALDI-TOF MS-based rapid AST was applied to determine the drug resistance at breakpoint concentration, although MS-MICs might shift to a low dilution. Thus, it is critical for patients to accelerate the AST result from two days to several hours.