Keeping labs proficient in the detection of invasive fungi
In June 2023, the US CDC published the first of communications regarding an outbreak of meningitis by Fusarium species in patients who had been exposed to contaminated epidural anesthesia in Matamoros, Tamaulipas, Mexico.
Officials identified two clinics associated with the outbreak; these clinics were closed and as of July 28, 2023 there were 151 persons under investigation, 10 suspected cases, 14 probable cases, 10 confirmed cases, and 9 deaths.
CMPT recently sent a Mycology Proficiency Testing challenge on Fusarium species. Here is an extract from the educational critique (MY2304-3 April 2023)
Fusarium species can be recovered easily on routine media, and there are no specific growth requirements. The colony is usually white and cottony but can develop a pink or violet centre; the reverse is usually light (Figure 1) however, Fusarium species can exhibit a remarkable degree of variation with respect to morphological and physiological characteristics. 1,2
Figure 1. Colony of Fusarium species on Sabouraud’s dextrose agar. A: front B: reverse.
PCR has emerged as both a sensitive and specific test for the diagnosing of Fusarium infections. 3,4 Some methods allow for rapid species identification aiding in the selection of appropriate treatment as certain species, like Fusarium solani, have shown to have a worse prognosis and higher resistance to voriconazole. 5
Matrix-assisted laser desorption/ionization time of flight-mass spectrometry (MALDI-ToF MS) is a rapid and reliable tool for the identification of microorganisms, allowing the identification of fungal isolates within minutes. 6,7 Several studies have been conducted on Fusarium species with high success rates of 82%‒99%.8 It is important particularly for species that are uncommonly recovered that each laboratory validate their own MALDI-ToF MS system (usually at least five isolates) of the suspected species before using this method to report such strains to the species level.8
In vitro susceptibility testing of Fusarium is becoming increasingly important because of frequency and diversity of infections and because resistance profiles are species-specific. Reference methods for antifungal susceptibility testing have been established by Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility (EUCAST).
Because different Fusarium species show different tendencies in their susceptibility against various antifungal compounds,9 susceptibility testing should be included in particularly in severe infections. 10
- Larone Davise H. Medically Important Fungi. A Guide to Identification 5th Ed. 4th ed. ASM Press; 2011.
- Nelson PE, Dignani MC, Anaissie EJ. Taxonomy, biology, and clinical aspects of Fusarium species. Clin Microbiol Rev. 1994;7(4):479-504.
- Manikandan P, Abdel-hadi A, Randhir Babu Singh Y, et al. Fungal Keratitis: Epidemiology, Rapid Detection, and Antifungal Susceptibilities of Fusarium and Aspergillus Isolates from Corneal Scrapings. Ilkit M, ed. BioMed Res Int. 2019;2019:6395840. doi:10.1155/2019/6395840
- Tananuvat N, Salakthuantee K, Vanittanakom N, Pongpom M, Ausayakhun S. Prospective comparison between conventional microbial work-up vs PCR in the diagnosis of fungal keratitis. Eye. 2012;26(10):1337-1343. doi:10.1038/eye.2012.162
- Oechsler RA, Feilmeier MR, Miller D, Shi W, Hofling-Lima AL, Alfonso EC. Fusarium keratitis: genotyping, in vitro susceptibility and clinical outcomes. Cornea. 2013;32(5):667-673. doi:10.1097/ICO.0b013e318277ac74
- Dingle TC, Butler-Wu SM. MALDI-TOF Mass Spectrometry for Microorganism Identification. Autom Emerg Technol Clin Microbiol. 2013;33(3):589-609. doi:10.1016/j.cll.2013.03.001
- Rohilla R, Meena S, Mohanty A, et al. Etiological spectrum of infectious keratitis in the era of MALDI-TOF-MS at a tertiary care hospital. J Fam Med Prim Care. 2020;9(9).
- Triest David, Stubbe Dirk, De Cremer Koen, et al. Use of Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry for Identification of Molds of the Fusarium Genus. J Clin Microbiol. 2015;53(2):465-476. doi:10.1128/jcm.02213-14
- Al-Hatmi AMS, van Diepeningen AD, Curfs-Breuker I, de Hoog GS, Meis JF. Specific antifungal susceptibility profiles of opportunists in the Fusarium fujikuroi complex. J Antimicrob Chemother. 2015;70(4):1068-1071. doi:10.1093/jac/dku505
- Espinel-Ingroff A., Colombo A. L., Cordoba S., et al. International Evaluation of MIC Distributions and Epidemiological Cutoff Value (ECV) Definitions for Fusarium Species Identified by Molecular Methods for the CLSI Broth Microdilution Method. Antimicrob Agents Chemother. 2016;60(2):1079-1084. doi:10.1128/aac.02456-15