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Beyond culture: What is matrix-assisted laser desorption ionization time of flight mass spectrometry?
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Pathogen identification remains a challenge and culture methods have limitations. Novel molecular methods have become clinically available. Matrix-assisted laser desorption ionization-time of flight mass spectrometry — MALDI-TOF — is a new technology for rapid and cost-effective identification of microorganisms, including those implicated in periprosthetic joint infection. Current methods for identification of pathogens rely upon costly and time-consuming culture techniques. MALDI-TOF exploits the proteome of microorganisms for pathogen recognition. It is efficient for implementation at the large institution-level and can precisely classify microorganisms down to the strain.
MALDI-TOF uses mass spectroscopy to analyze large biologic molecules. Ultraviolet light is emitted onto culture samples in a prepared matrix, which is vaporized producing protonated ions from analytes, which are separated by mass-to-charge ratio. Time of flight analyzers create a picture profile from the spectrum produced by the analytes called a peptide mass fingerprint (PMF). Each micobe-specific PMF is subsequently matched with its corresponding PMF in the proteome database and used for identification.
In a study into the accuracy of MALDI-TOF in detecting species within a bacterial colony, MALDI-TOF correctly identified 95.4% of bacteria and 84.1% of these were correctly classified at the species level. Other studies found rates of accurate MALDI-TOF identification upward of 97.7%. Among cultures of periprosthetic joint infection (PJI) isolated from synovial fluid of septic and aseptic patients, MALDI-TOF correctly identified the species in 89% of cases, and the genus in an additional 2% of cases. There is value in this technique as an ancillary test for distinguishing true-positive culture results from false-positives due to contamination.
A cost-effectiveness study that examined annual microbiology laboratory activity demonstrated a reduction in half of annual expenditures associated with microorganism identification after MALDI-TOF use began. The initial expense of MALDI-TOF was offset within 3 years of laboratory use.
Orthopedic applications of MALDI-TOF are promising in PJI. It can be used for organism identification, and examining sensitivities and strain virulence. There is encouraging evidence in vivo for its use in staging biofilms and in the differentiation of planktonic cells vs. biofilm formation. More work, however, is needed to refine this technique before it can be definitively used as a diagnostic and decision-making tool in the PJI setting. Its use is reliant upon an updated and accurate proteomic database. However, it is still an invaluable instrument for any clinical microbiological laboratory.
- References:
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- For more information:
- Kier Blevins, BA; Karan Goswami, MD; and Javad Parvizi, MD, FRCS, can be reached at Rothman Institute at Thomas Jefferson University Hospital, Sheridan Building, Suite 1000, 125 S. 9th St., Philadelphia, PA 19107. Blevin’s email: kierblevins@gmail.com. Goswami’s email: karan.goswami@mail.com. Parvizi’s email: parvj@aol.com.
Disclosures: Blevins and Goswami report no relevant financial disclosures. Parvizi reports he is a paid consultant for Zimmer Biomet, ConvaTec, TissueGene, CeramTec and Ethicon; has stock options with Parvizi Surgical Innovations, Hip Innovation Technology, CD Diagnostics, CorenTec, Alphaeon, Joint Purification Systems, Ceribell, MedAp, MicroGenDx, Cross Current Business Intelligence, Invisible Sentinel, Physician Recommended Nutriceuticals and Intellijoint; he receives royalties from CorenTec, Datatrace, Elsevier, Jaypee, SLACK Incorporated and Wolters Kluwer.