Mass spectrometry — a technology for the characterization and detection of organic molecules — has evolved to the detection of large biomolecules, ranging from structural proteins to large protein complexes. The invention of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) technology enables scientists to determine the nucleotide, or fingerprint, of proteins associated with different diseases.
The sensitivity of MALDI-TOF MS for the detection of proteins to femtomolar range (1 femtomolar = 10-15 molar), rapid detection time, and low cost of operation provided a new horizon for the use of MALDI-TOF MS. An important advance made with this technology is the ability to analyze whole cells or crude cell extracts which eliminates the manual-processing steps needed for enriching proteins.
Having rapid and accurate microbial identification to improve and target patient therapy made clear the potential for microbial identification where the microbes can be placed directly onto the target slide without purification steps.
In MALDI-TOF, a sample is mixed with another compound called the matrix. This mixture is applied to a metal plate and irradiated with a laser. The mixture absorbs the laser light and vaporizes, along with the sample. In this process, the sample is ionized.
An electric field is applied to lift these ions into the time-of-flight mass spectrometer, which separates them according to their mass and charge, displaying the results as a series of peaks or spectra which correspond to different proteins and peptides expressed by the organism. These proteins provide a unique fingerprint that is used to identify a specific organism being tested.
Ongoing development of MALDI-TOF
While the first commercially available MALDI-TOF system was launched in 1988, the first study for use of MALDI-TOF MS for bacterial identification took place in 1996. A wide range of studies followed — from enhancing protocols to building a database of organisms identified using MALDI-TOF MS.
Another important component in utilizing the system for microbial identification was the creation of the first validated reference database introduced in 1998 by AnagnosTec. The database was needed to match or compare spectra generated from the organism tested to the database’s reference spectra corresponding to a specific microbial identification.
Updates to the database quickly followed, expanding identification for rare and newly emerging pathogens. A key feature in developing the database is having an intelligent algorithm that can differentiate between organism-specific peaks versus commonly expressed proteins.
By integrating a particular knowledge base of infectious agents into a MALDI-TOF platform, the goal among clinical-laboratory innovators is to apply mass spectrometry for microbial identification in order to create a microorganism-identification system that can perform faster compared to standard laboratory methods. Such a solution would become part of a full microbiology laboratory-automation solution, interconnected using a middleware solution to improve connectivity, information exchange, and workflow.
Dramatic shift in lab ID methods
MALDI-TOF MS use for microbial identification provides a leap forward in the field of microbiology from a diagnostic and patient-outcome perspective. Application of this technology in the microbiology lab will offer rapid results that can be provided to physicians within minutes, generating the microbial identification needed to target patient therapy effectively. The simple workflow and high-throughput capabilities of MALDI-TOF MS can enable a laboratory to increase testing capacity without adding costs.
Expanded testing capabilities enable the lab to test bacteria, yeast, fungi, mycobacterium, and other organisms. This technology for microbial identification is generally recognized to provide highly accurate and reproducible results compared to conventional methods. Commonly used growth media do not interfere with the identification results.
MALDI-TOF mass spectrometry, when applied to our understanding of microorganisms, holds the potential to provide a dramatically improved alternative to traditional laboratory identification methods for microorganisms in the process of medical diagnosis. The speed, robustness, and minimal costs of sample prep and measurement make this solution ideal for high-throughput use.
Nedal Safwat, PhD,
is the marketing manager for bioM’erieux in Durham, NC.
Andrew N. Eaton, PhD,
is the MALDI sales and marketing manager for Shimadzu is headquartered in Kyoto, Japan. The two companies have partnered to integrate bioM’erieux’s knowledge base of infectious agents into the MALDI-TOF platform for a full microbiology laboratory automation solution.