System for Identification of Filamentous Fungi Evaluated

The utilization of matrix-assisted laser desorption/ionization – time of flight (MALDI-TOF) mass spectrometry has the potential to speed up and improve the accuracy of identification of filamentous fungi.

Invasive fungal infections are an important cause of morbidity and mortality affecting primarily immunocompromised patients. While fungal identification to the species level is critical to providing appropriate therapy, it can be slow, laborious, and often relies on subjective morphologic criteria.

A team of collaborating scientists led by those at the ARUP Laboratories (Salt Lake City, UT, USA) in a multi-center study used MALDI-TOF mass spectrometry, to evaluate the accuracy of the system in identifying 1,601 clinical mold isolates as compared to identification by DNA sequence analysis and supported by morphologic and phenotypic testing.

The team used the VITEK MS v3.0 system (bioMérieux, Marcy l'Etoile. France) to correctly identify 91% of 1,519 samples to the species level of isolates representing organisms in the v3.0 database. An additional 27 isolates (2%) were correctly identified to the genus level. Fifteen isolates were incorrectly identified, either due to a single incorrect identification or multiple identifications from different genera. In those cases, when a single identification was provided that was not correct, the misidentification was within the same genus. The VITEK MS v3.0 was unable to identify 91 (6%) isolates, despite repeat testing. These isolates were distributed among all the genera.

Jenna Rychert, PhD, a research and development scientist and lead author of the study, said, “While speed is commonly cited as a major advantage of MALDI methods in the bacterial ID space, this is less of a factor with molds. As clinicians still have to take the organism of interest through the culturing process. However, in cases where clinicians aren't able to make an identification based on their visual inspection of the organism's morphology, using MALDI could allow them to skip the various additional, and time-consuming, tests required to further evaluating the organism.”

Dr. Rychert added, “I think if you compare the performance of the Vitek MS to someone who is a trained mycologist who has been looking at cultures for 20 years, it's probably not a whole lot different. But if you compare it to a whole mycology laboratory that has everyone from someone who just got out of school to that 20-year veteran, it's going to give you a more accurate answer more of the time.” The study was published on November 27, 2017, in the Journal of Clinical Microbiology.