Semi-quantitative MALDI-TOF for antimicrobial susceptibility testing in Staphylococcus aureus

Abstract

Antibiotic resistant bacterial infections are a significant problem in the healthcare setting, in many cases requiring the rapid administration of appropriate and effective antibiotic therapy. Diagnostic assays capable of quickly and accurately determining the pathogen resistance profile are therefore crucial to initiate or modify care. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) is a standard method for species identification in many clinical microbiology laboratories and is well positioned to be applied towards antimicrobial susceptibility testing. One recently reported approach utilizes semi-quantitative MALDI-TOF MS for growth rate analysis to provide a resistance profile independent of resistance mechanism. This method was previously successfully applied to Gram-negative pathogens and mycobacteria; here, we evaluated this method with the Gram-positive pathogen Staphylococcus aureus. Specifically, we used 35 strains of S. aureus and four antibiotics to optimize and test the assay, resulting in an overall accuracy rate of 95%. Application of the optimized assay also successfully determined susceptibility from mock blood cultures, allowing both species identification and resistance determination for all four antibiotics within 3 hours of blood culture positivity.

Proof of Concept for MBT ASTRA, a Rapid Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry (MALDI-TOF MS)-Based Method To Detect Caspofungin Resistance in Candida albicans and Candida glabrata

“…Standard AFST by microdilution methods takes at least 24 h, but the application of MALDI-TOF MS may accelerate susceptibility testing. So far, rapid susceptibility testing by MALDI-TOF MS has mainly been described for bacteria (23,27,(30)(31)(32)(33). One research group has reported on a rapid AFST approach by analyzing the similarities of the MALDI-TOF MS profile spectra derived from different setups containing increasing antibiotic concentrations (34)(35)(36).…”

“…MBT ASTRA is a semiquantitative method that was first applied for the detection of meropenem susceptibility in bacteria derived from culture plates or from positive blood cultures within 1 to 4 h (32). Subsequently, additional studies demonstrating the successful applicability of MBT ASTRA for detection of strains resistant to gentamicin, cefotaxime (37), and rifampin (31,38) were performed. In all these studies, the time to the result was significantly reduced from at least 24 h to 3 to 6 h by use of the MALDI-TOF MS approach.…”

Antimicrobial susceptibility testing: currently used methods and devices and the near future in clinical practice

“…However, the first attempts to use mass spectrometry for micro-organism identification date back to 1975 (Anhalt and Fenselau 1975). In recent years, MALDI-TOF MS has been introduced into clinical microbiology laboratories as a time-and cost-saving method based on the determination of mass/charge (m/z) ratio and strain differentiation using their ribosomal proteins (Maxson et al 2017). MALDI-TOF MS does not depend on metabolic activity and can directly identify within minutes colonies of Gram-positive and Gram-negative bacteria and yeasts grown on agar plates (Wieser et al 2012).…”

Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry for the Rapid Detection of Antimicrobial Resistance Mechanisms and Beyond

“…The assay yielded almost 100% sensitivity and specificity for all antibiotics evaluated, with poorer results for piperacillintazobactam. Identification of bacteria and analysis of susceptibility are possible within 4 h. In another study, Maxson et al applied this method for the first time to study the susceptibilities of 35 S. aureus isolates to several antibiotics, such as ciprofloxacin, oxacillin, cefepime, and vancomycin (116). The incubation time was established as 2 h, and the resistance breakpoints for classifying the isolates were based on current guidelines from the CLSI (117).…”