Multicenter evaluation of the VITEK MS matrix-assisted laser desorption/ionization-time of flight mass spectrometry system for identification of bacteria, including Brucella, and yeasts

Rapid detection of antimicrobial resistance in methicillin-resistant Staphylococcus aureus using MALDI-TOF mass spectrometry

Antimicrobial resistance is a growing problem in modern healthcare. Most antimicrobial susceptibility tests (AST) require long culture times which delay diagnosis and effective treatment. Our group has previously reported a proof-of-concept demonstration of a rapid AST in Escherichia coli using deuterium labeling and MALDI mass spectrometry. Culturing bacteria in D2O containing media incorporates deuterium in newly synthesized lipids, resulting in a mass shift that can be easily detected by mass spectrometry. The extent of new growth is measured by the average mass of synthesized lipids that can be correlated with resistance in the presence of antimicrobials. In this work, we adapt this procedure to methicillin-resistant Staphylococcus aureus using the Bruker MALDI-TOF Biotyper, a low-cost instrument commonly available in diagnostic laboratories. The susceptible strain showed a significant decrease in average mass in on-target microdroplet cultures after 3 hours of incubation with 10 µg/mL methicillin, while the resistant strain showed consistent labeling regardless of methicillin concentration. This assay allows us to confidently detect methicillin resistance in S. aureus after only 3 hours of culture time and minimal sample processing, reducing the turn-around-time significantly over conventional assays. The success of this work suggests its potential as a rapid AST widely applicable in many clinical microbiology labs with minimal additional costs.

Evaluation of Formic Acid Sandwich (FA-sandwich), A Pretreatment method for Filamentous Fungi, for the Identification of Clinically Relevant Filamentous Fungi by Two MALDI-TOF MS systems

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been successfully applied to identify microorganisms. However, unlike bacteria and yeast where identification results can be obtained rapidly and accurately by using a simple direct-coating pretreatment method, the traditional pretreatment methods for filamentous fungi are more complex, involving ethanol, formic acid, acetonitrile, and a protein extraction process by centrifugation, i.e., the EtOH-FA full extraction. This cumbersome pretreatment for filamentous fungi is a major reason for the lack of widespread use of MALDI-TOF MS for the identification of filamentous fungi in clinical settings. The present study describes an alternative method, the FA-sandwich, and demonstrates that the approach is efficient and effective. 148 clinical filamentous fungal isolates collected from three large general hospitals in Hubei Province, China, were processed by the FA-sandwich method and identified by two MALDI-TOF MS platforms, Autof ms and Vitek MS. The FA-sandwich allowed a 93.9% species-level identification with Autof ms, and 97.3% species-level identification rates were found for Vitek MS when the IVD, the RUO and in-house databases are used in combination. Further comparison of the ease of FA-sandwich with the EtOH-FA full extraction showed that the FA-sandwich is a more convenient, time- and reagent-saving, and sensitive pretreatment method. These findings indicate that the FA-sandwich method is suitable for pretreating filamentous fungi followed by MALDI-TOF MS identification in clinical microbiology laboratories.