Real-time PCR TaqMan assay for detectingTrichophyton tonsurans, a causative agent of tinea capitis, from hairbrushes

S1 guidelines: Tinea capitis

Tinea capitis describes a dermatophyte infection of scalp and hair that predominately occurs in children. The diagnostic workup includes microscopic examination, culture and/or molecular tests. Treatment is guided by the specific organism involved and should consist of systemic agents as well as adjuvant topical treatment. The aim of the present update of the interdisciplinary German S1 guidelines is to provide dermatologists, pediatricians and general practitioners with a decision tool for selecting and implementing appropriate diagnostic and therapeutic measures in patients with tinea capitis. The guidelines were developed based on current international guidelines, in particular the 2010 European Society for Pediatric Dermatology guidelines and the 2014 British Association of Dermatologists guidelines, as well as on a review of the literature conducted by the guideline committee. This multidisciplinary committee consists of representatives from the German Society of Dermatology (DDG), the German-Speaking Mycological Society (DMykG), the German Society for Hygiene and Microbiology (DGHM), the German Society of Pediatric and Adolescent Medicine (DGKJ) and the German Society for Pediatric Infectious Diseases (DGPI). The Division of Evidence-based Medicine (dEBM) provided methodological assistance. The guidelines were approved by the participating medical societies following a comprehensive internal and external review.

Scalp microbiota in members of a Japanese high school judo team including Trichophyton tonsurans carriers

Trichophyton tonsurans is a major causative fungus of human dermatophytosis, which has been isolated from contact sport players in Japan. The microbiome in the scalp of judoists with or without T. tonsurans infection was analyzed to investigate the correlation between T. tonsurans infection and microbiome profile. Among 30 members of the same judo team in a high school, samples were collected by scrubbing their scalp with shampoo hairbrushes; then, DNA was extracted directly from the obtained scales. Twenty-seven datasets were subjects for microbiome analysis and T. tonsurans was detected in six members (no T. tonsurans-positive participants had scalp lesions). Regarding the fungal microbiome, Cyphellophora were more abundant in the T. tonsurans-positive group (TP) than T. tonsurans-negative group (TN) (P < 0.05). Regarding the Malassezia microbiome, Malassezia caprae were more abundant in TP than TN (P < 0.01). Regarding the bacterial microbiome, Lactococcus, Actinobacillus, Beijerinckiaceae and Xanthomonas were more abundant in TP than TN (P < 0.05). Also, the Shannon diversity index revealed no significant diversity between TP and TN, and 3-D principal coordinate analysis revealed no clear separation between TP and TN. There was practically no difference in microbiome between TP and TN, indicating that T. tonsurans could colonize humans regardless of their original microbiome. T. tonsurans coexisted with other fungi and bacteria without affecting species diversity in asymptomatic carriers. To our knowledge, this is the first investigation of the correlation between T. tonsurans infection and microbiome profile.

Development a diagnostic pan-dermatophyte TaqMan probe real-time PCR assay based on beta tubulin gene

Early differentiation of dermatophytosis from other cutaneous mycoses is essential to avoid inaccurate therapy. DNA-based techniques including real-time PCR have increasingly been considered for detection of fungal elements in clinical specimens. In this study, after partial sequence analysis of beta tubulin (BT2) gene in 13 common and rare pathogenic dermatophyte species, a pan-dermatophyte primer and probe set was designed in a TaqMan probe-based PCR format. The sensitivity and specificity of the system was tested with 22 reference strains of dermatophytes, 234 positive clinical specimens, 32 DNA samples extracted from normal nails, several fungi other than dermatophytes and human DNAs. Analytical detection limit of the designed PCR on serially diluted DNAs of prepared recombinant plasmid indicated that only five molecules per sample are the minimum number for reliable detection by the assay. A total of 226 out of 234 (96.5%) DNAs extracted from clinical samples, but none of the 32 nail samples, from healthy volunteers were positive in PCR. The real-time PCR targeted beta tubulin gene established in this study could be a sensitive diagnostic tool which is significantly faster than the conventional culture method and should be useful in the clinical settings, in large-scale epidemiological studies and in clinical trials of antifungal therapy.

Detection and identification of Trichophyton tonsurans from clinical isolates and hairbrush samples by loop-mediated isothermal amplification system

Since the 1990s, there have been reports of the spread of dermatophytosis caused by Trichophyton tonsurans among contact sports athletes in several countries, including Japan. This study was performed to develop a loop-mediated isothermal amplification (LAMP) system for rapid and accurate detection and identification of T. tonsurans from clinical isolates or hairbrush samples for diagnosis and to prevent the spread of infection. A specific primer set was prepared by comparing the whole genome sequence of T. tonsurans with those of six other closely related dermatophytes. After confirming the sensitivity and specificity of this system, LAMP assay was performed using 37 clinical samples obtained from three healthy volunteers and 24 judo athletes. A total of 155 fungal isolates (56 strains of various standard fungi, 96 identified T. tonsurans isolates, three hairbrush-cultured isolates from judo athletes) and 37 hairbrush samples (34 samples from 24 judo athletes, and three samples from three healthy volunteers) were used for culture and LAMP assay, respectively. The assay showed no cross-reactivity to standard strains other than T. tonsurans. The detection limit was 100 copies of DNA template per tube. All of the 96 T. tonsurans isolates were amplified, and all samples from healthy volunteers showed negative results. Four of the 34 hairbrush samples obtained from judo athletes showed positive results in LAMP assay, and two of the four were positive in both culture and LAMP assay. We developed a rapid LAMP system with high specificity and sensitivity for diagnosis of T. tonsurans infection.

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.

Asymptomatic dermatophyte scalp carriage: laboratory diagnosis, epidemiology and management

Asymptomatic carrier is defined as an individual who has dermatophyte-positive scalp culture without signs or symptoms of tinea capitis. The prevalence of asymptomatic carriage differs from region to region with a rate of 0.1-49%. Anthropophilic dermatophytes, Trichophyton tonsurans and Trichophyton violaceum, have been generally associated with high rates of asymptomatic carriage. Hence, the presence of dermatophytes on healthy scalp hairs of children may be a potential source of infection for schoolmates, playmates and/or households. Although it was also reported in adults, most carriage has been observed in children especially among those between 4 and 8 years of age, while male to female ratios vary between studies. It is still unclear, whether carriers should be treated with topical antifungal shampoos or oral antifungals or both, as some studies indicate that some untreated cases become culture-negative after 2-12 months. This review provides details on related dermatophyte fungi, laboratory diagnosis, epidemiology, ways of spreading as well as treatment and follow-up results of asymptomatic carriage. An integration into the school health programs is proposed, which will render the possible dealing of the subject in a comprehensive and reasonable manner.

Diagnosis of common dermatophyte infections by a novel multiplex real-time polymerase chain reaction detection/identification scheme

BACKGROUND

In the absence of a functional dermatophyte-specific polymerase chain reaction (PCR), current diagnosis of dermatophytoses, which constitute the commonest communicable diseases worldwide, relies on microscopy and culture. This combination of techniques is time-consuming and notoriously low in sensitivity.

OBJECTIVES

Recent dermatophyte gene sequence records were used to design a real-time PCR assay for detection and identification of dermatophytes in clinical specimens in less than 24 h.

PATIENTS AND METHODS

Two assays based on amplification of ribosomal internal transcribed spacer regions and on the use of probes specific to relevant species and species-complexes were designed, optimised and clinically evaluated. One assay was for detecting the Trichophyton mentagrophytes species complex plus T. tonsurans and T. violaceum. The second assayed for the T. rubrum species complex, Microsporum canis and M. audouinii.

RESULTS

The analytical sensitivity of both assays was 0.1 pg DNA per reaction, corresponding to 2.5-3.3 genomes per sample. The protocol was clinically evaluated over 6 months by testing 92 skin, nail and hair specimens from 67 patients with suspected dermatophytosis. Real-time PCR detected and correctly identified the causal agent in specimens from which T. rubrum, T. interdigitale, M. audouinii or T. violaceum grew in culture, and also identified a dermatophyte species in an additional seven specimens that were negative in microscopy and culture.

CONCLUSIONS

This highly sensitive assay also proved to have high positive and negative predictive values (95.7% and 100%), facilitating the accurate, rapid diagnosis conducive to targeted rather than empirical therapy for dermatophytoses.