Fast and sensitive detection of Trichophyton rubrum DNA from the nail samples of patients with onychomycosis by a double-round polymerase chain reaction-based assay

Deep Learning Assisted Diagnosis of Onychomycosis on Whole-Slide Images

Background: Onychomycosis numbers among the most common fungal infections in humans affecting finger- or toenails. Histology remains a frequently applied screening technique to diagnose onychomycosis. Screening slides for fungal elements can be time-consuming for pathologists, and sensitivity in cases with low amounts of fungi remains a concern. Convolutional neural networks (CNNs) have revolutionized image classification in recent years. The goal of our project was to evaluate if a U-NET-based segmentation approach as a subcategory of CNNs can be applied to detect fungal elements on digitized histologic sections of human nail specimens and to compare it with the performance of 11 board-certified dermatopathologists. Methods: In total, 664 corresponding H&E- and PAS-stained histologic whole-slide images (WSIs) of human nail plates from four different laboratories were digitized. Histologic structures were manually annotated. A U-NET image segmentation model was trained for binary segmentation on the dataset generated by annotated slides. Results: The U-NET algorithm detected 90.5% of WSIs with fungi, demonstrating a comparable sensitivity with that of the 11 board-certified dermatopathologists (sensitivity of 89.2%). Conclusions: Our results demonstrate that machine-learning-based algorithms applied to real-world clinical cases can produce comparable sensitivities to human pathologists. Our established U-NET may be used as a supportive diagnostic tool to preselect possible slides with fungal elements. Slides where fungal elements are indicated by our U-NET should be reevaluated by the pathologist to confirm or refute the diagnosis of onychomycosis.

Comparison of Samples of Blister Fluid and Scales in the diagnosis of dermatomycosis

BACKGROUND

The successful diagnosis of dermatomycosis depends on specimen collection. Dermatomycosis is sampled mainly for scales, but there is a lack of research on specimens of blister fluid.

OBJECTIVES

To explore whether blister fluid can diagnose dermatomycosis and compare blister fluid and scale specimens for dermatomycosis diagnosis.

METHODS

From April to July 2021, we prospectively gathered 34 patients who needed to meet all inclusion criteria simultaneously and collected their blister fluid and scales as specimens. The two samples were tested by fluorescent stain microscopy, fungal culture, and PCR, and the diagnosis results were compared.

RESULTS

The blister fluid sample's sensitivity, specificity, and accuracy were 90%, 100%, and 94.1%, respectively, whereas the scales sample were 60%, 100%, and 76.5%, respectively. The positive likelihood ratios were>10 for both blister fluid and scales specimen, and the negative likelihood ratios were not < 0.1. On the Youden's index, the blister fluid specimen was 90%, and the scales specimen was 60%. As for the diagnostic odds ratio, both of them were >1. By fungal culture, we detected 14 cases of fungi in blister fluid and eight in scales. On PCR, 22 cases of fungi in blister fluid and ten in scales were identified.

CONCLUSIONS

This study demonstrated that a sample of blister fluid had better sensitivity, accuracy, and Youden's index in diagnosing dermatomycosis with blister fluid. Collection of blister fluid might compensate for the inadequacy of collecting only scales specimens for mycological testing.

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

Background. PCR assays have been developed for the diagnosis of dermatophytes, yet data in African populations are scarce. Objective. This study aimed to compare two PCR assays for the diagnosis of dermatophytosis in outpatients at the Aristide Le Dantec University Hospital in Dakar, Senegal. Patients and methods. A total of 105 samples, including 24 skin, 19 nail and 62 hair samples collected from 99 patients were included in this study. Each sample was subjected to conventional diagnosis (CD), including direct microscopy and culture, and two real-time PCR assays: one in-house (IH)-PCR, used at the University Hospital of Marseille and the Eurobio Scientific commercial kit (CK): designed for the specific detection of six dermatophytes not including Microsporum audouinii. Results. Of the 105 specimens, 24.8%, 36.2% and 20% were positive by CD, IH-PCR and CK-PCR, respectively. The IH-PCR and CK-PCR exhibited 88.9% and 65.4% sensitivity, respectively. With a 36.6 diagnostic odd ratio and 1.41 needed to diagnose, the IH-PCR displayed better diagnostic indices than the CK-PCR. It is notable that, when considering the species that it claims to detect, when it came to skin and nail samples, CK-PCR sensitivity increased to 77%. Conclusions. The pan-dermatophyte IH-PCR performed better in the diagnosis of dermatophytosis in this African population than the CK-PCR, which is not designed to detect M. audouinii. Nevertheless, both assays exhibited similarly good diagnostic indices for tinea corporis and tinea unguium, both of which are localisations where M. audouinii is more rarely involved than in tinea capitis.

Nondermatophyte mould onychomycosis

Nondermatophyte moulds (NDMs) onychomycosis is often difficult to diagnose as NDMs have been considered contaminants of nails. There are several diagnostic methods used to identify NDMs, however, repeated laboratory isolation is recommended to validate pathogenicity. With NDM and mixed infection (dermatophytes plus NDM) onychomycosis on the rise, accurate clinical diagnosis along with mycological tests is recommended. Systemic antifungal agents such as itraconazole and terbinafine (e.g. pulse regimen: 1 pulse = every day for one week, followed by no treatment for three weeks) have shown efficacy in treating onychomycosis caused by various NDMs such as Aspergillus spp., Fusarium spp., Scopulariopsis brevicaulis, and Onychocola canadensis. Studies investigating topical therapy and devices for NDM onychomycosis are limited. The emergence of antifungal resistance necessitates the incorporation of antifungal susceptibility testing into diagnosis when possible, for the management of recalcitrant infections. Case studies documented in the literature show newer azoles such as posaconazole and voriconazole as sometimes effective in treating resistant NDM onychomycosis. Treatment with broad-spectrum antifungal agents (e.g. itraconazole and efinaconazole) and other combination therapy (oral + oral and/or oral + topical) may be considerations in the management of NDM onychomycosis.

A Practical Guide to Curing Onychomycosis: How to Maximize Cure at the Patient, Organism, Treatment, and Environmental Level

Onychomycosis is a fungal nail infection caused by dermatophytes, non-dermatophyte molds, and yeasts. Treatment of this infection can be difficult, with relapse likely to occur within 2.5 years of cure. The objective of this article is to review factors that can impact cure and to suggest practical techniques that physicians can use to maximize cure rates. Co-morbidities, as well as disease severity and duration, are among the many patient factors that could influence the efficacy of antifungal therapies. Furthermore, organism, treatment, and environmental factors that may hinder cure include point mutations, biofilms, affinity for non-target enzymes, and exposure to fungal reservoirs. To address patient-related factors, physicians are encouraged to conduct confirmatory testing and treat co-morbidities such as tinea pedis early and completely. To combat organism-focused factors, it is recommended that disruption of biofilms is considered, and drugs with multiple routes of delivery and unique mechanisms of action are prescribed when traditional agents are not effective. Extending follow-up periods, using combination treatments, and considering pulse regimens may also be of benefit. Through these practical techniques, physicians can maximize cure and limit the risk of relapse and re-infection.

Diagnosis of Superficial Mycoses by a Rapid and Effective PCR Method from Samples of Scales, Nails and Hair

Superficial mycoses are the most frequently diagnosed affections of the stratum corneum of the skin, nails and hair. It is generally caused by the presence of yeasts and dermatophytes. Onychomycosis is the most common infection with an incidence of 80-90% in Europe generally produced by Trichophyton rubrum. The aim of this study is to compare the traditional diagnostic techniques of superficial mycoses with a homemade and wide-spectrum fungal polymerase chain reaction (PCR) technique that amplifies a specific region of the 18S ribosomal RNA (rRNA) directly from samples of scales, nails and hair. A total of 626 clinical samples (obtained in the Basurto University Hospital, Bilbao, Spain) were analysed by traditional culture, microscopy and PCR. DNA extraction was carried out by using an extraction buffer and bovine serum, and amplification of samples and performance of the PCR were checked by conventional agarose gel electrophoresis with subsequent sequencing of amplified samples. A total of 211 samples (34%) resulted in positive diagnosis with at least one of the two applied methods: culture (21%) and PCR (22%). Despite the low percentage of identification achieved by the sequencing technique (40%), the value contributed by the amplification of the 18S region of the rRNA was considered important in the identification as it showed a high predictive values for both positive and negative diagnoses (90.9% and 94.6%, respectively). The proposed PCR method has been confirmed as a complementary, rapid, and effective method in the diagnosis of superficial mycoses. Additionally, it reduces the time to obtain satisfactory results from 4 weeks to 7 h.

Confirmatory Testing Prior to Initiating Onychomycosis Therapy Is Cost-Effective

Background:

Onychomycosis can be investigated by sampling. Information gleaned includes nail bed involvement, nail plate penetration, fungal viability, and species identification. Testing samples can confirm a diagnosis. While diagnostic testing is considered useful in directing therapy, a substantial number of clinicians do not confirm diagnosis prior to treatment.

Objectives:

The aim of this study is to quantify the benefit of confirmatory testing prior to treating toenail onychomycosis.

Methods:

The cost of mycological cure (negative potassium hydroxide and negative culture) and the cost-effectiveness of confirmatory testing were determined using the average cost of potassium hydroxide (KOH), culture, periodic acid–Schiff (PAS), efinaconazole, ciclopirox, terbinafine, and itraconazole. Costs were obtained through literature searches, public domain websites, and telephone surveys to local pharmacies and laboratories. To represent the potential risks of prescribing onychomycosis treatment, the costs associated with liver monitoring, potential life-threatening adverse events, and drug-drug interactions were obtained through public domain websites, published studies, and product inserts.

Results:

PAS was determined to be the most sensitive confirmatory test and KOH the least expensive. The overall cost of an incorrect diagnosis (no confirmatory test used) ranged between $350 and $1175 CAD per patient for treatment of 3 infected toenails. Comparatively, performing confirmatory testing prior to treatment decreases the overall cost to $320 to $930, depending on the therapy, physician, and test.

Conclusions:

It is preferred to diagnose onychomycosis prior to treatment. Furthermore, there are cost savings when confirmatory testing is performed before initiating treatment with both topical and oral antifungals in Canada.

Onychomycosis InfectionsDo Polymerase Chain Reaction and Culture Reports Agree?

BACKGROUND

Mycological culture is the traditional method for identifying infecting agents of onychomycosis despite high false-negative results, slower processing, and complications surrounding nondermatophyte mold (NDM) infections. Molecular polymerase chain reaction (PCR) methods are faster and suited for ascertaining NDM infections.

METHODS

To measure agreement between culture and PCR methods for identification of infecting species of suspected onychomycosis, single toenail samples from 167 patients and repeated serial samples from 43 patients with suspected onychomycosis were processed by culture and PCR for identification of 16 dermatophytes and five NDMs. Agreement between methods was quantified using the kappa statistic (κ).

RESULTS

The methods exhibited fair agreement for the identification of all infecting organisms (single samples: κ = 0.32; repeated samples: κ = 0.38). For dermatophytes, agreement was moderate (single samples: κ = 0.44; repeated samples: κ = 0.42). For NDMs, agreement was poor with single samples (κ = 0.16) but fair with repeated samples (κ = 0.25). Excluding false-negative reports from analyses improved agreement between methods in all cases except the identification of NDMs from single samples.

CONCLUSIONS

Culture was three or four times more likely to report a false-negative result compared with PCR. The increased agreement between methods observed by excluding false-negative reports statistically clarifies and highlights the major discord caused by false-negative cultures. The increased agreement of NDM identification from poor to fair with repeated sampling along with their poor agreement in the single samples, with and without false-negatives, affirms the complications of NDM identification and supports the recommendation that serial samples help confirm the diagnosis of NDM infections.

Onychomycosis in the 21st Century: An Update on Diagnosis, Epidemiology, and Treatment

Onychomycosis accounts for 50% of all nail disease cases and is commonly caused by dermatophytes. Diabetes, human immunodeficiency virus, immunosuppression, obesity, smoking, and advancing age are predisposing factors of this fungal infection. Potassium hydroxide and culture are considered the current standard for diagnosing onychomycosis, revealing both fungal viability and species identification. Other diagnostic tests currently available include periodic acid-Schiff staining, polymerase chain reaction techniques, and fluorescent staining. Across 6 recently published epidemiology studies, the global prevalence of onychomycosis was estimated to be 5.5%, falling within the range of previously reported estimates (2%-8%). Newly approved onychomycosis treatments include efinaconazole, tavaborole, and laser therapy with lasers only approved to temporarily increase the amount of clear nail. Additional onychomycosis treatments being investigated include iontophoresis and photodynamic therapy with small open-label studies reported thus far. Preventative strategies, to help decrease recurrence and reinfection rates, include sanitisation of footwear and prophylactic topical antifungal agents.

Reappraisal of Conventional Diagnosis for Dermatophytes

Dermatophytoses include a wide variety of diseases involving glabrous skin, nails and hair. These superficial infections are a common cause of consultation in dermatology. In many cases, their diagnosis is not clinically obvious, and mycological analysis therefore is required. Direct microscopic examination of the samples using clearing agents provides a quick response to the clinician and is usually combined with cultures on specific media, which must be used to overcome the growth of contaminating moulds that may hamper the recovery of dermatophytes. Accurate identification of the causative agent (i.e. at the species level), currently based on morphological criteria, is necessary not only to initiate an appropriate treatment but also for setting prophylactic measures. However, conventional methods often lack sensitivity and species identification may require up to 4 weeks if subcultures are needed. Histological analysis, which is considered the "gold standard" for the diagnosis of onychomycoses, is seldom performed, and as direct examination, it does not allow precise identification of the pathogen. Nevertheless, a particular attention to the quality of clinical specimens is warranted. Moreover, the sensitivity of direct examination may be greatly enhanced by the use of fluorochromes such as calcofluor white. Likewise, sensitivity of the cultures could be enhanced by the use of culture media containing antifungal deactivators. With the generalization of molecular identification by gene sequencing or MALDI-TOF mass spectrometry, the contribution of historical biochemical or physiological tests to species identification of atypical isolates is now limited. Nevertheless, despite the recent availability of several PCR-based kits and an extensive literature on molecular methods allowing the detection of fungal DNA or both detection and direct identification of the main dermatophyte species, the biological diagnosis of dermatophytosis in 2016 still relies on both direct examination and cultures of appropriate clinical specimens.

Diagnosis of Dermatophytosis Using Molecular Biology

Identification of fungi in dermatological samples using PCR is reliable and provides significantly improved results in comparison with cultures. It is possible to identify the infectious agent when negative results are obtained from cultures. In addition, identification of the infectious agent can be obtained in 1 day. Conventional and real-time PCR methods used for direct fungus identification in collected samples vary by DNA extraction methods, targeted DNA and primers, and the way of analysing the PCR products. The choice of a unique method in a laboratory is complicated because the results expected from skin and hair sample analysis are different from those expected in cases of onychomycosis. In skin and hair samples, one dermatophyte among about a dozen possible species has to be identified. In onychomycosis, the infectious agents are mainly Trichophyton rubrum and, to a lesser extent, Trichophyton interdigitale, but also moulds insensitive to oral treatments used for dermatophytes, which renders fungal identification mandatory. The benefits obtained with the use of PCR methods for routine analysis of dermatological samples have to be put in balance with the relative importance of getting a result in a short time, the price of molecular biology reagents and equipment, and especially the time spent conducting laboratory manipulations.

Molecular determination of mixed infections of dermatophytes and nondermatophyte molds in individuals with onychomycosis

BACKGROUND

Reports of mixed infections with nondermatophyte molds (NDMs) and dermatophytes in onychomycosis are rare, possibly owing to the inhibition of NDM growth during traditional culture. We sought to determine the prevalence of mixed infections in onychomycosis using molecular identification.

METHODS

Molecular analyses were used to identify infecting organisms directly from at least two serial great toenail samples from each of the 44 patients.

RESULTS

Mixed infections were present in 41% of the patients (18 of 44). A single coinfecting NDM was the most common mixed infection and was detected in 34% of patients with onychomycosis (15 of 44), with Fusarium oxysporum present in 14% (6 of 44), Scopulariopsis brevicaulis in 9% (4 of 44), Acremonium spp in 2% (1 of 44), Aspergillus spp in 4.5% (2 of 44), and Scytalidium spp in 4.5% (2 of 44). Mixed infections with two NDMs were found in 7% of patients (3 of 44).

CONCLUSIONS

Mixed onychomycosis infections may be more prevalent than previously reported.

Using a polymerase chain reaction as a complementary test to improve the detection of dermatophyte fungus in nails

BACKGROUND

Dermatomycoses are a group of pathologic abnormalities frequently seen in clinical practice, and their prevalence has increased in recent decades. Diagnostic confirmation of mycotic infection in nails is essential because there are several pathologic conditions with similar clinical manifestations. The classical method for confirming the presence of fungus in nail is microbiological culture and the identification of morphological structures by microscopy.

METHODS

We devised a nested polymerase chain reaction (PCR) that amplifies specific DNA sequences of dermatophyte fungus that is notably faster than the 3 to 4 weeks that the traditional procedure takes. We compared this new technique and the conventional plate culture method in 225 nail samples. The results were subjected to statistical analysis.

RESULTS

We found concordance in 78.2% of the samples analyzed by the two methods and increased sensitivity when simultaneously using the two methods to analyze clinical samples. Now we can confirm the presence of dermatophyte fungus in most of the positive samples in just 24 hours, and we have to wait for the result of culture only in negative PCR cases.

CONCLUSIONS

Although this PCR cannot, at present, substitute for the traditional culture method in the detection of dermatophyte infection of the nails, it can be used as a complementary technique because its main advantage lies in the significant reduction of time used for diagnosis, in addition to higher sensitivity.

Quantification of dermatophyte viability for evaluation of antifungal effect by quantitative PCR

Dermatophytosis is a common disease caused by dermatophyte fungi such as Trichophyton rubrum and Trichophyton mentagrophytes. A method of quantifying fungal viability in the lesions of dermatophytosis is indispensable for understanding the therapeutic process and outcome; however, no such method has yet been developed. The aim of this study was to develop a method for quantifying dermatophyte viability by quantitative polymerase chain reaction (qPCR). The internal transcribed spacer (ITS) and D1/D2 regions, including each of rRNA and rDNA, were chosen as the targets, and dermatophyte-specific primer pairs were designed corresponding to ITS and D1/D2 regions. The amounts of target RNA and DNA after heat or antifungal treatment were measured by qPCR and compared with colony-forming unit (CFU) counts. RNA and DNA could extract from dermatophytes by mechanical pulverization of conidia using a Multi-Beads Shocker cell disruptor. Our method was sufficiently sensitive to detect 10 copies by qPCR using both ITS and D1/D2 primer pairs. The most sensitive target was ITS-cDNA after heat or antifungal treatment, and essentially consistent with CFU counts. On the other hands, ITS-DNA and D1/D2-DNA were not decreased soon after heat or antifungal treatment, but those were decreased significantly and reflected the CFU counts after 48 h of antifungal treatment. We conclude that ITS-cDNA is useful mainly for quantifying dermatophyte viability at early responses, but ITS-DNA and D1/D2-DNA are also available for evaluation, which does not need an early response.

Multiplex PCR assay for the detection of common dermatophyte nail infections

Onychomycosis is one of the most prevalent dermatophytic diseases. Mycological methods used in the conventional diagnosis may not be optimal. Multiplex (MX) PCR was reported as a reliable alternative. Dermatophyte gene sequence records were used to design a MX PCR for detection and identification of dermatophytes in nail specimens. A MX PCR method based on the amplification of the chitin synthase 1 and internal transcribed spacer genes was developed. The study included 93 strains of dermatophytes and non-dermatophytic fungi, six dermatophytic reference strains and 201 nail specimens from patients with dermatophytic onyxis. DNA extraction directly from nail samples was carried out by using the QIAamp DNA extraction kit (Quiagen). A set of primers was designed and their specificity was assessed. MX PCR detected the causal agent in specimens from which Trichophyton rubrum and T. interdigitale grew in culture and also identified a dermatophyte species in an additional 32 specimens that were negative in microscopy and culture. None of the investigated non-dermatophytic strains was positive. Sensitivity of MX PCR was higher as compared to mycological examination (97% vs. 81.1%). MX PCR for direct detection of dermatophytes from nail samples yielded mixed flora in 32.8% of samples. MX PCR proved sensitive and adequate for the diagnosis of dermatophytic onychomycosis. It is much adapted to cases where culture is negative or contaminated by overgrowing moulds, which makes the identification of the causal agent problematic.

Molecular diagnosis of dermatophyte infections

PURPOSE OF REVIEW

Recent advances in the molecular diagnostics of dermatophytosis may improve speed, specificities and sensitivities. This review provides an update on the current available molecular techniques for the diagnosis of dermatophytosis.

RECENT FINDINGS

Molecular diagnostics of dermatophytosis relate to the direct detection of dermatophyte DNA in clinical specimens. Important challenges have been associated with the DNA extraction procedures, which despite improvement still lack consensus, and the fact that phenotypic species classification not always translates into distinct molecular taxonomic entities. Molecular methods are divided into conventional PCR, real-time PCR and post-PCR techniques. The former benefits from simplicity and being less expensive to implement, real-time PCR is less laborious, may enable a broader spectrum of simultaneous species detections and the closed system reduces contamination risk, whereas post-PCR strategies may increase the number of species identified but prolong the turnaround time, and the processing of PCR products increases the laboratory contamination risk.

SUMMARY

Current molecular methods are on the verge of overcoming most of the early challenges regarding dermatophyte taxonomy, DNA extraction procedures and species specificity, and thus may lead to an increased adoption of such methods. This may point towards a novel consensus in which molecular methods supplement or even replace classical diagnosis of dermatophytosis.

Identification of infectious agents in onychomycoses by PCR-terminal restriction fragment length polymorphism

A fast and reliable assay for the identification of dermatophyte fungi and nondermatophyte fungi (NDF) in onychomycosis is essential, since NDF are especially difficult to cure using standard treatment. Diagnosis is usually based on both direct microscopic examination of nail scrapings and macroscopic and microscopic identification of the infectious fungus in culture assays. In the last decade, PCR assays have been developed for the direct detection of fungi in nail samples. In this study, we describe a PCR-terminal restriction fragment length polymorphism (TRFLP) assay to directly and routinely identify the infecting fungi in nails. Fungal DNA was easily extracted using a commercial kit after dissolving nail fragments in an Na(2)S solution. Trichophyton spp., as well as 12 NDF, could be unambiguously identified by the specific restriction fragment size of 5'-end-labeled amplified 28S DNA. This assay enables the distinction of different fungal infectious agents and their identification in mixed infections. Infectious agents could be identified in 74% (162/219) of cases in which the culture results were negative. The PCR-TRFLP assay described here is simple and reliable. Furthermore, it has the possibility to be automated and thus routinely applied to the rapid diagnosis of a large number of clinical specimens in dermatology laboratories.

A rationale for systemic treatment in onychomycosis with negative results on fungal examination

BACKGROUND

Fungal infection of the nail affects millions of people worldwide, and has an estimated prevalence of about 10% of the general population. Laboratory confirmation of fungal infection is currently accepted as a requirement before initiation of antifungal treatment in clinical practice.

AIM

To examine the rationale for systemic treatment in cases of clinical onychomycosis with negative results on fungal examination (potassium hydroxide test and fungal culture).

METHODS

In total, 147 patients with suspected clinical toenail onychomycosis but with negative results on fungal examination underwent up to three consecutive fungal examinations of the affected nails. Patients who were negative after these examinations underwent a fourth set of investigations, including PCR.

RESULTS

Of the 147 cases initially thought to be negative, 138 (94%) were rated as positive after up to four consecutive sets of laboratory mycological investigations including PCR. Trichophyton rubrum was by far the commonest dermatophyte cultured from all samples.

CONCLUSIONS

In the majority of cases of initially negative examinations, consecutive laboratory fungal tests will eventually produce positive results. These findings suggest that systemic antifungal treatment should be started in patients with suspected fungal infections, even if they have negative laboratory fungal examinations.

Direct detection of five common dermatophyte species in clinical samples using a rapid and sensitive 24-h PCR-ELISA technique open to protocol transfer

Identification of dermatophytes is usually based on morphological characteristics determined by time-consuming microscopic and cultural examinations. An effective PCR-ELISA method has been developed for rapid detection of dermatophyte species directly from clinical specimens within 24 h. Isolated genomic DNA of skin scrapings and nail samples from patients with suspected dermatophyte infections is amplified with species-specific digoxigenin-labelled primers targeting the topoisomerase II gene. The subsequent ELISA procedure with biotin-labelled probes allows a sensitive and specific identification of the five common dermatophytes -Trichophyton rubrum, T. interdigitale, T. violaceum, Microsporum canis and Epidermophyton floccosum. PCR-ELISA, based on the new polyphasic species concept, was assessed using 204 microscopy-positive samples in two university mycological laboratories in Munich and Tübingen, and 316 consecutive specimens - regardless of mycological findings - in a dermatological practice laboratory in Neu-Ulm. One of the five dermatophytes was confirmed by PCR-ELISA in 163 of 204 (79.9%) of the clinical samples from the university hospitals found positive using microscopy. Culture was positive for dermatophytes in 59.8% of the same cases. A significant difference between these two methods could be demonstrated using the McNemar test (P < 0.005). Analysis of specimens from Neu-Ulm confirmed the results in a dermatological practice laboratory as 25.0% of the specimens had positive PCR results, whereas only 7.3% were positive according to culture. Direct DNA isolation from clinical specimens and the PCR-ELISA method employed in this study provide a rapid, reproducible and sensitive tool for detection and discrimination of five major dermatophytes at species level, independent of morphological and biochemical characteristics.

Molecular detection of dermatophytes and nondermatophytes in onychomycosis by nested polymerase chain reaction based on 28S ribosomal RNA gene sequences

BACKGROUND

Onychomycosis is often caused by dermatophytes, but the role of nondermatophytes is underestimated due to the difficulty of identifying them by conventional direct microscopy and culture.

OBJECTIVES

This study aims to detect nondermatophytes, as well as dermatophytes, in the nail samples of patients with onychomycosis using a polymerase chain reaction (PCR)-based culture-independent method.

MATERIALS AND METHODS

The nested PCR assay targeting the sequence of the 28S ribosomal RNA gene was used to amplify fungal DNAs from 50 microscopy-positive nail specimens. Newly designed primer sets for dermatophyte universal, Trichophyton rubrum, T. mentagrophytes, Aspergillus spp., Scopulariopsis brevicaulis, Fusarium solani, F. oxysporum, F. verticillioides, Candida albicans and C. tropicalis were used after confirmation of their specificity.

RESULTS

Forty-seven cases (94%) were positive for fungal DNA, among which dermatophytes were detected in 39 cases (83.0%): T. rubrum in 35 cases (74.5%) and T. mentagrophytes in eight cases (17.0%). Surprisingly, nondermatophytes were detected in 18 cases (38.3%), both dermatophytes and nondermatophytes in 10 cases (21.3%) and nondermatophytes alone in eight cases (17.0%). Aspergillus spp. alone was observed in five cases (10.6%).

CONCLUSIONS

This study indicates that most of the affected nail plates of patients with onychomycosis were positive for specific fungal DNAs, and suggests that nondermatophytes detected at high rates may be involved in the pathogenesis of onychomycosis.

[What's new in clinical dermatology]

This selection reviews several topics in the news: - in internal medicine, the cardiovascular and pulmonary risk factors in progressive systemic sclerosis (circulating lupus anticoagulant, smoking, NT-pro BNP marker); the relations between lupus erythematous and polymorphic light eruption, or Jessner-Kanof syndrome; the diagnostic score of autoinflammatory syndromes; and the dysmetabolism syndrome of psoriasis; - in infectious diseases, the return of epidemic typhus; the emergence of TIBOLA rickettsiosis; the development of methicillin-resistant Staphylococcus aureus strains in both the nosocomial and community settings; and finally news on herpes group viral infections.

Diagnosis of Trichophyton rubrum from onychomycotic nail samples using polymerase chain reaction and calcofluor white microscopy

BACKGROUND

A high rate of false-negative dermatophyte detection is observed when the most common laboratory methods are used. These methods include microscopic observation of potassium hydroxide-digested nail clippings and culture methods using agar-based media supplemented with cycloheximide, chloramphenicol, and gentamicin to isolate dermatophytes. Microscopic detection methods that use calcofluor white staining or periodic acid-Schiff staining may also be substituted for and have previously been reported to be more sensitive than potassium hydroxide-digested nail clippings.

METHODS

Trichophyton rubrum infections were detected directly from nails in a double-round polymerase chain reaction assay that uses actin gene-based primers. This method was compared with detection of fungal hyphae by using calcofluor white fluorescence microscopy of nail samples collected from 83 patients with onychomycosis who were undergoing antifungal drug therapy.

RESULTS

Twenty-six of 83 samples (31.3%) were found to be positive by calcofluor white fluorescence microscopy, and 21 of 83 samples (25.3%) yielded positive results for T rubrum when actin gene-based primers in a double-round polymerase chain reaction assay were used. When calcofluor white fluorescence microscopy and polymerase chain reaction assay were used, the combined detection was 46.9% compared with 31.3% when calcofluor microscopy and culture of nail samples on Sabouraud's dextrose agar supplemented with cycloheximide, chloramphenicol, and gentamicin were used.

CONCLUSIONS

These results suggest that the use of a direct DNA protocol is an alternative method for detecting Trichophyton infections. When this protocol is used, the presence of T rubrum DNA is directly detected. However, the viability of the dermatophyte is not addressed, and further methods need to be developed for the detection of viable T rubrum directly from nail samples.

Validation of PCR-reverse line blot, a method for rapid detection and identification of nine dermatophyte species in nail, skin and hair samples

A dermatophyte-specific PCR-reverse line blot (PCR-RLB) assay based on internal transcribed sequences was developed. This assay allows the rapid detection and identification of nine clinically relevant species within the three dermatophyte genera Trichophyton, Microsporum and Epidermophyton in nail, skin and hair samples within 1 day. Analysis of 819 clinical samples (596 nail, 203 skin and 20 hair) revealed a positive PCR-RLB result in 93.6% of 172 culture-positive and microscopy-positive samples. PCR-RLB was superior to culture and direct microscopy, in both detection and species identification. Comparison of identification results of 208 PCR-positive and culture-positive clinical samples showed five discrepancies (2.4%) between PCR-RLB identification and classical microscopic/biochemical identification of isolates. Comparison of PCR-RLB identification and classical identification of 98 other isolates (dermatophytes and non-dermatophytes) revealed 13 discrepancies (13.3%) and five incomplete identifications of Trichophyton spp. Sequence analysis of ITS1 regions of 23 samples with discrepant or incomplete identification results (four Centraalbureau voor Schimmelcultures dermatophyte strains, four clinical samples and 15 clinical isolates) confirmed identification results of PCR-RLB in 21 of the 23 analyzed samples. PCR-RLB proved to be extremely suitable for routine detection and identification of dermatophytes directly in nail, skin and hair samples because it is rapid, sensitive, specific and accurate.