Laboratories around the world are quickly embracing MALDI-TOF MS as a fast, easy, cost-effective and accurate way to identify grown bacteria and fungi, based on mass distribution of bacterial proteins in cultured bacteria or fungi, according to a new review published in Clinical Chemistry. In the past, identifying bacteria and fungi has been a challenging process with many steps, depending on the organism.
In MALDI (matrix-assisted laser desorption ionization), a matrix “assists in the desorption and ionization of microbial analytes through the energy of a laser,” wrote author Robin Patel in “MALDI-TOF MS for the Diagnosis of Infectious Diseases.” Patel is director of the infectious diseases research laboratory at Mayo Clinic in Rochester, Minnesota.
“As a result of being ‘shot’ by the laser, microbial and matrix molecules are desorbed, with the majority of energy being absorbed by the matrix, converting it to an ionized state.” Then, random collision in the gas phase occurs, and the charge is transferred from matrix to microbial molecules. “The ionized microbial molecules are accelerated, based on mass-to-charge ratio, into a TOF (time-of-flight) mass analyzer, a tube under vacuum,” she explained.
Next, ions travel toward an ion detector, “with smaller analytes reaching the detector first, followed by progressively larger analytes,” Patel said. “A mass spectrum is generated, representing the number of ions of a given mass impacting the ion detector over time.”
Recent commercial and regulatory developments for MALDI-TOF MS make the technology more easily accessible to laboratories. VITEK MS and the MALDI Biotyper CA System both were cleared in the last two years by the U.S. Food and Drug Administration, according to Patel.
“The technology is automated, high throughput, and applicable to a broad range of common as well as esoteric bacteria and fungi,” wrote Patel. “MALDI-TOF MS is an incontrovertibly beneficial technology for the clinical microbiology laboratory.” It was developed quickly for use in clinical microbiology laboratories, and “iterative improvements continue to improve its performance for microbial identification,” which can make it difficult to interpret scientific literature on the subject, according to Patel.
“The technology “performs at least as well as, if not better than, automated biochemical identification for commonly encountered bacteria and yeast,” the review states, and it has become the “method of choice for identification of anaerobic bacteria.” Many clinical microbiology laboratories previously did not have tools available to identify this type of bacteria, so the ability to do so using MALDI-TOF MS can help to inform interpretation of the clinical significance and susceptibility of anaerobes. It can also be used to identify mycobacteria, with some limitations.
Read the review online.