Diagnosis of dermatophytes: from microscopy to direct PCR
Sarah E. Kidd A and Gerhard F. Weldhagen AA National Mycology Reference Centre, Microbiology and Infectious Diseases, SA Pathology, Frome Road, Adelaide, SA 5000, Australia.
Sarah Kidd is the Head of the National Mycology Reference Centre at SA Pathology, as well as Adjunct Senior Lecturer at the University of Adelaide. She completed a Bachelor of Medical Science with Honours (1999) and a PhD in Medicine (2003), both at the University of Sydney, and has undertaken postdoctoral training and research at the University of British Columbia, Vancouver, Canada, and at Monash University–The Alfred Hospital, Melbourne. She is a Fellow of the Australian Society for Microbiology (FASM), Secretary of the Australia and New Zealand Mycoses Interest Group (ANZMIG), convenes the biennial Mycology Masterclass, and provides mycology expertise to the Royal College of Pathologists of Australasia Quality Assurance Programs. |
Gerhard Weldhagen is the supervising pathologist for the National Mycology Reference Centre at SA Pathology. He completed his undergraduate studies in 1993, receiving a Bachelor’s degree in Medicine and Surgery (MBChB) from the University of Pretoria, South Africa. This was followed by a Master’s degree in Clinical Microbiology (MMed (Path) cum laude) and subsequently a PhD in Microbiology, conferred by the University of Pretoria in 2002 and 2005 respectively. After settling in Australia during 2009, a Fellowship of the Royal College of Pathologists of Australasia (FRCPA) was attained during the same year. Current interests include the role of molecular assays in diagnostic microbiology, including mycology. |
Microbiology Australia 43(1) 9-13 https://doi.org/10.1071/MA22005
Submitted: 31 December 2021 Accepted: 5 February 2022 Published: 8 April 2022
© 2022 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the ASM. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)
Abstract
Dermatophyte fungi are a common cause of skin, nail and hair infections globally, ranging from mild to cosmetically disfiguring, or even invasive infections in rare cases. Specimens requiring fungal microscopy and culture for suspected dermatophyte infection make up a significant portion of the workload in diagnostic microbiology laboratories. Whilst still considered the gold standard, a dermatophyte culture-based method is labour intensive, has poor sensitivity, slow result turnaround time and requires significant expertise for identification of the fungi. Molecular diagnostics, especially real-time PCR, have the potential to improve diagnostic sensitivity, reduce labour requirements and decrease result turnaround times. Despite these advantages, a PCR-based approach may present some difficulties and disadvantages, most notably its diagnostic range and incompatibility with oral therapy prescribing requirements under the Pharmaceutical Benefits Scheme. Here we review current best practices and future prospects for laboratory diagnosis of dermatophyte infections, including the role of microscopy, culture and direct PCR.
Keywords: dermatophyte, Epidermophyton, fungal culture, medical mycology, microscopy, Microsporum, onychomycosis, real-time PCR, tinea pedis, Trichophyton.
References
[1] Ghannoum, MA et al.. (2000) A large-scale North American study of fungal isolates from nails: the frequency of onychomycosis, fungal distribution, and antifungal susceptibility patterns. J Am Acad Dermatol 43, 641–648.| A large-scale North American study of fungal isolates from nails: the frequency of onychomycosis, fungal distribution, and antifungal susceptibility patterns.Crossref | GoogleScholarGoogle Scholar | 11004620PubMed |
[2] Ilkit, M and Durdu, M (2015) Tinea pedis: the etiology and global epidemiology of a common fungal infection. Crit Rev Microbiol 41, 374–388.
| Tinea pedis: the etiology and global epidemiology of a common fungal infection.Crossref | GoogleScholarGoogle Scholar | 24495093PubMed |
[3] Nowicka, D and Nawrot, U (2021) Tinea pedis-An embarrassing problem for health and beauty: a narrative review. Mycoses 64, 1140–1150.
| Tinea pedis-An embarrassing problem for health and beauty: a narrative review.Crossref | GoogleScholarGoogle Scholar | 34145648PubMed |
[4] Teo, TSP et al.. (2021) Mycetoma caused by Microsporum canis in a patient with renal transplant: a case report and review of the literature. Transpl Infect Dis 23, e13516.
| Mycetoma caused by Microsporum canis in a patient with renal transplant: a case report and review of the literature.Crossref | GoogleScholarGoogle Scholar | 33217133PubMed |
[5] Wang, R et al.. (2021) Invasive dermatophyte infection: a systematic review. Mycoses 64, 340–348.
| Invasive dermatophyte infection: a systematic review.Crossref | GoogleScholarGoogle Scholar | 33217082PubMed |
[6] Thomas, J et al.. (2010) Toenail onychomycosis: an important global disease burden. J Clin Pharm Ther 35, 497–519.
| Toenail onychomycosis: an important global disease burden.Crossref | GoogleScholarGoogle Scholar | 20831675PubMed |
[7] Bongomin, F et al.. (2018) A review of onychomycosis due to Aspergillus species. Mycopathologia 183, 485–493.
| A review of onychomycosis due to Aspergillus species.Crossref | GoogleScholarGoogle Scholar | 29147866PubMed |
[8] Ellis, DH et al.. (1997) Non-dermatophytes in onychomycosis of the toenails. Br J Dermatol 136, 490–493.
| Non-dermatophytes in onychomycosis of the toenails.Crossref | GoogleScholarGoogle Scholar | 9155945PubMed |
[9] Shemer, A et al.. (2009) New criteria for the laboratory diagnosis of nondermatophyte moulds in onychomycosis. Br J Dermatol 160, 37–39.
| New criteria for the laboratory diagnosis of nondermatophyte moulds in onychomycosis.Crossref | GoogleScholarGoogle Scholar | 18764841PubMed |
[10] Pharmaceutical Benefits Scheme (PBS) (2021) General schedule, antifungals for systemic use, Terbinafine. Available at https://www.pbs.gov.au/medicine/item/2285G-2804N-4011D [Accessed 23 December 2021]
[11] Weitzman, I and Summerbell, RC (1995) The dermatophytes. Clin Microbiol Rev 8, 240–259.
| The dermatophytes.Crossref | GoogleScholarGoogle Scholar | 7621400PubMed |
[12] Weinberg, JM et al.. (2003) Comparison of diagnostic methods in the evaluation of onychomycosis. J Am Acad Dermatol 49, 193–197.
| Comparison of diagnostic methods in the evaluation of onychomycosis.Crossref | GoogleScholarGoogle Scholar | 12894064PubMed |
[13] Haghani, I et al.. (2013) Comparison of diagnostic methods in the evaluation of onychomycosis. Mycopathologia 175, 315–321.
| Comparison of diagnostic methods in the evaluation of onychomycosis.Crossref | GoogleScholarGoogle Scholar | 23371413PubMed |
[14] Public Health England (2016) UK Standards for Microbiology Investigations. SMI B39. Investigation of Dermatological Specimens for Superficial Mycoses. Available at https://www.gov.uk/government/publications/smi-b-39-investigation-of-dermatological-specimens-for-superficial-mycoses [Accessed 13 December 2021]
[15] Ghannoum, M et al.. (2018) Examining the importance of laboratory and diagnostic testing when treating and diagnosing onychomycosis. Int J Dermatol 57, 131–138.
| Examining the importance of laboratory and diagnostic testing when treating and diagnosing onychomycosis.Crossref | GoogleScholarGoogle Scholar | 28653769PubMed |
[16] Bruker Daltonics GmbH & Co. KG. (2021) MBT Filamentous Fungi Library 4.0 Release Notes. Revision D Doc. no. 5027071.
[17] L’Ollivier, C et al.. (2013) A MALDI-TOF MS procedure for clinical dermatophyte species identification in the routine laboratory. Med Mycol 51, 713–720.
| A MALDI-TOF MS procedure for clinical dermatophyte species identification in the routine laboratory.Crossref | GoogleScholarGoogle Scholar | 23611419PubMed |
[18] Shaw, D (2021) Matrix-assisted laser desorption/ionisation-time of flight mass spectrometry: protocol standardisation, comparison and database expansion for faster and reliable identification of dermatophytes. Mycoses 64, 926–935.
| Matrix-assisted laser desorption/ionisation-time of flight mass spectrometry: protocol standardisation, comparison and database expansion for faster and reliable identification of dermatophytes.Crossref | GoogleScholarGoogle Scholar | 33851439PubMed |
[19] Normand, AC et al.. (2018) Nucleotide sequence database comparison for routine dermatophyte identification by internal transcribed spacer 2 genetic region DNA barcoding. J Clin Microbiol 56, e00046–18.
| Nucleotide sequence database comparison for routine dermatophyte identification by internal transcribed spacer 2 genetic region DNA barcoding.Crossref | GoogleScholarGoogle Scholar | 29491019PubMed |
[20] Arabatzis, M et al.. (2007) Diagnosis of common dermatophyte infections by a novel multiplex real-time polymerase chain reaction detection/identification scheme. Br J Dermatol 157, 681–689.
| Diagnosis of common dermatophyte infections by a novel multiplex real-time polymerase chain reaction detection/identification scheme.Crossref | GoogleScholarGoogle Scholar | 17672875PubMed |
[21] Ross, IL et al.. (2020) Detection and identification of dermatophyte fungi in clinical samples using a commercial multiplex tandem PCR assay. Pathology 52, 473–477.
| Detection and identification of dermatophyte fungi in clinical samples using a commercial multiplex tandem PCR assay.Crossref | GoogleScholarGoogle Scholar | 32307094PubMed |
[22] Lin, BB et al.. (2021) Multiplex RT-PCR provides improved diagnosis of skin and nail dermatophyte infections compared to microscopy and culture: a laboratory study and review of the literature. Diagn Microbiol Infect Dis 101, 115413.
| Multiplex RT-PCR provides improved diagnosis of skin and nail dermatophyte infections compared to microscopy and culture: a laboratory study and review of the literature.Crossref | GoogleScholarGoogle Scholar | 34256251PubMed |
[23] Kabtani, J et al.. (2021) Real-time PCR assay for the detection of dermatophytes: comparison between an in-house method and a commercial kit for the diagnosis of dermatophytoses in patients from Dakar, Senegal. J Fungi (Basel) 7, 949.
| Real-time PCR assay for the detection of dermatophytes: comparison between an in-house method and a commercial kit for the diagnosis of dermatophytoses in patients from Dakar, Senegal.Crossref | GoogleScholarGoogle Scholar |
[24] Cuchí-Burgos, E et al.. (2021) Commercial real time PCR implementation for rapid diagnosis of onychomycosis: a new workflow in a clinical laboratory. Enferm Infecc Microbiol Clin (Engl Ed) 39, 326–329.
| Commercial real time PCR implementation for rapid diagnosis of onychomycosis: a new workflow in a clinical laboratory.Crossref | GoogleScholarGoogle Scholar | 34353508PubMed |
[25] Spiliopoulou, A et al.. (2015) Evaluation of a commercial PCR test for the diagnosis of dermatophyte nail infections. J Med Microbiol 64, 25–31.
| Evaluation of a commercial PCR test for the diagnosis of dermatophyte nail infections.Crossref | GoogleScholarGoogle Scholar | 25418736PubMed |
[26] Hayette, MP et al.. (2019) Clinical evaluation of the DermaGenius® Nail real-time PCR assay for the detection of dermatophytes and Candida albicans in nails. Med Mycol 57, 277–283.
| Clinical evaluation of the DermaGenius® Nail real-time PCR assay for the detection of dermatophytes and Candida albicans in nails.Crossref | GoogleScholarGoogle Scholar | 29762721PubMed |
[27] Laroche, L et al.. (2021) Epidemiological analysis of nail aspergillosis and non-dermatophyte moulds. Criteria for the involvement of Aspergillus in 102 cases of onychomycosis at Montpellier University Hospital, France (1991–2019). Mycoses 64, 1546–1553.
| Epidemiological analysis of nail aspergillosis and non-dermatophyte moulds. Criteria for the involvement of Aspergillus in 102 cases of onychomycosis at Montpellier University Hospital, France (1991–2019).Crossref | GoogleScholarGoogle Scholar | 34467565PubMed |
[28] Moreno, G and Arenas, R (2010) Other fungi causing onychomycosis. Clin Dermatol 28, 160–163.
| Other fungi causing onychomycosis.Crossref | GoogleScholarGoogle Scholar | 20347658PubMed |
[29] Singh, A et al.. (2021) Evaluation of DermaGenius® resistance real-time polymerase chain reaction for rapid detection of terbinafine-resistant Trichophyton species. Mycoses 64, 721–726.
| Evaluation of DermaGenius® resistance real-time polymerase chain reaction for rapid detection of terbinafine-resistant Trichophyton species.Crossref | GoogleScholarGoogle Scholar | 33760310PubMed |
[30] The European Committee on Antimicrobial Susceptibility Testing (2020) Overview of antifungal ECOFFs and clinical breakpoints for yeasts, moulds and dermatophytes using the EUCAST E.Def 7.3, E.Def 9.3 and E.Def 11.0 procedures. Version 2. Available at http://www.eucast.org
