Rapid detection of Arthroderma vanbreuseghemii in rabbit skin specimens by PCR?RFLP

Recent trends in rapid diagnostic techniques for dermatophytosis

Dermatophytosis is a common contagious disease of both humans and animals. It is caused by a group of filamentous fungi known as dermatophytes, including several genera and various species. An accurate diagnosis of dermatophytes as a causative agent of a skin lesion requires up to one month of conventional laboratory diagnostics. The conventional gold standard diagnostic method is a direct microscopic examination followed by 3 to 4 weeks of Sabouraud's dextrose agar (SDA) culturing, and it may require further post-culturing identification through biochemical tests or microculture technique application. The laborious, exhaustive, and time-consuming gold standard method was a real challenge facing all dermatologists to achieve a rapid, accurate dermatophytosis diagnosis. Various studies developed more rapid, accurate, reliable, sensitive, and specific diagnostic tools. All developed techniques showed more rapidity than the classical method but variable specificities and sensitivities. An extensive bibliography is included and discussed through this review, showing recent variable dermatophytes diagnostic categories with an illustration of weaknesses, strengths, and prospects.

Relationship Between Phenotypic and Genotypic Characteristics of Trichophyton mentagrophytes Strains Isolated from Patients with Dermatophytosis

According to epidemiological, clinical and mycological criteria, it has long been admitted that the Trichophyton mentagrophytes species includes two varieties: a zoophilic variety (var. mentagrophytes) and an anthropophilic variety (var. interdigitale) that involve the upper and the lower part of the body, respectively. The further application of molecular techniques to the characterization of dermatophyte strains showed that this classification is unreliable. The aim of our study was to assess the usefulness of PCR-RFLP (restriction fragment length polymorphism) and sequencing in the characterization of T. mentagrophytes strains taken from Tunisian patients. The study was carried out in 2008 in the laboratory of Parasitology-Mycology of Farhat Hached University Hospital, Sousse, Tunisia. A total of 133 strains were isolated from 133 patients addressed to the laboratory for dermatological lesions very evocative of dermatomycosis. Eighty strains were isolated from lesions located on the lower part of the body (onychomycosis, tinea pedis) and 53 strains from the upper part of the body (tinea capitis, tinea corporis). All strains were submitted to mycological examination (direct microscopic examination and culture on Sabouraud medium) and further investigated by using RFLP analysis of the PCR-amplified ITS1-5.8 s-ITS2 region of the ribosomal DNA and the MvaI restriction enzyme. In addition, 62 strains were further submitted to a sequencing of the ITS1-5.8 s-ITS2 region. On the basis of mycological criteria, all strains were diagnosed as T. mentagrophytes. All strains produced the same RFLP pattern and were identified as T. mentagrophytes interdigitale regardless of the location of lesions. Out of the 62 sequenced strains, 16 were found anthropophilic and 46 were zoophilic. In conclusion, all strains provisionally diagnosed as T. mentagrophytes on the basis of mycological criteria were shown to belong to T. interdigitale by using PCR-RFLP and sequencing irrespective of the site of lesions. The predominance of zoophilic strains needs further investigation.

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.

Validation of High Resolution Melting Analysis (HRM) of the Amplified ITS2 Region for the Detection and Identification of Yeasts from Clinical Samples: Comparison with Culture and MALDI-TOF Based Identification

AIM

Candida species are known as opportunistic pathogens, and a possible cause of invasive infections. Because of their species-specific antimycotic resistance patterns, reliable techniques for their detection, quantification and identification are needed. We validated a DNA amplification method for direct detection of Candida spp. from clinical samples, namely the ITS2-High Resolution Melting Analysis (direct method), by comparing it with a culture and MALDI-TOF Mass Spectrometry based method (indirect method) to establish the presence of Candida species in three different types of clinical samples.

MATERIALS AND METHODS

A total of 347 clinical samples, i.e. throat swabs, rectal swabs and vaginal swabs, were collected from the gynaecology/obstetrics, intensive care and haematology wards at the Ghent University Hospital, Belgium. For the direct method, ITS2-HRM was preceded by NucliSENS easyMAG DNA extraction, directly on the clinical samples. For the indirect method, clinical samples were cultured on Candida ID and individual colonies were identified by MALDI-TOF.

RESULTS

For 83.9% of the samples there was complete concordance between both techniques, i.e. the same Candida species were detected in 31.1% of the samples or no Candida species were detected in 52.8% of the samples. In 16.1% of the clinical samples, discrepant results were obtained, of which only 6.01% were considered as major discrepancies. Discrepancies occurred mostly when overall numbers of Candida cells in the samples were low and/or when multiple species were present in the sample.

DISCUSSION

Most of the discrepancies could be decided in the advantage of the direct method. This is due to samples in which no yeast could be cultured whereas low amounts could be detected by the direct method and to samples in which high quantities of Candida robusta according to ITS2-HRM were missed by culture on Candida ID agar. It remains to be decided whether the diagnostic advantages of the direct method compensate for its disadvantages.

An improved molecular diagnostic assay for canine and feline dermatophytosis

The few studies attempting to specifically characterize dermatophytes from hair samples of dogs and cats using PCR-based methodology relied on sequence-based analysis of selected genetic markers. The aim of the present investigation was to establish and evaluate a PCR-based approach employing genetic markers of nuclear DNA for the specific detection of dermatophytes on such specimens. Using 183 hair samples, we directly compared the test results of our one-step and nested-PCR assays with those based on conventional microscopy and in vitro culture techniques (using the latter as the reference method). The one step-PCR was highly accurate (AUC > 90) for the testing of samples from dogs, but only moderately accurate (AUC = 78.6) for cats. A nested-PCR was accurate (AUC = 93.6) for samples from cats, and achieved higher specificity (94.1 and 94.4%) and sensitivity (100 and 94.9%) for samples from dogs and cats, respectively. In addition, the nested-PCR allowed the differentiation of Microsporum canis from Trichophyton interdigitale (zoophilic) and geophilic dermatophytes (i.e., Microsporum gypseum or Trichophyton terrestre), which was not possible using the one step-assay. The PCRs evaluated here provide practical tools for diagnostic applications to support clinicians in initiating prompt and targeted chemotherapy of dermatophytoses.

Arthroderma vanbreuseghemii infection in three family members with kerion and tinea corporis

We present a familial infection caused by Arthroderma vanbreuseghemii. The proband is a 4-year-old boy, who had played with rabbits at his rabbit-farm neighbor. He complained of pruritus and pain in his scalp, which displayed redness, alopecia and painful cysts and eventually discharged pus and scabbed. Several erythema on his face and abdomen were also presented. He was diagnosed as having impetigo but antibacterial agents were not effective and his clinical condition did not improve. Several days later, his parents also developed facial erythema and scaling. The development of a kerion in the boy and tinea corporis in his parents were diagnosed based on the positive KOH examination. Morphologic and biochemical characteristics confirmed that their infections were caused by the zoophilic Trichophyton mentagrophytes, while sequencing of the internal transcribed spacer (ITS) 1/4 polymerase chain reaction products, amplified from primary culture isolates, established its Arthroderma vanbreuseghemii lineage. Random amplified polymorphic DNA (RAPD) analysis indicated these isolates might be the same strain and that infection cruciata occurred in this family. Semi-quantitative analysis of these strains indicated multiple and main enzymatic activities of alkaline phosphatase, beta-glucosaccharase. The boy was cured through treatment with itraconazole 100 mg/day orally in combination with topical washes with 2% ketoconazole shampoo, and his parents were successfully treated by topical application of terbinafine cream.

Evaluation of internal transcribed spacer 2-RFLP analysis for the identification of dermatophytes

A total of 95 isolates, belonging to 33 species of five dermatophyte genera, i.e. Arthroderma (15 species), Chrysosporium (two), Epidermophyton (one), Microsporum (three) and Trichophyton (12), were studied using internal transcribed spacer 2 (ITS2)-PCR-RFLP analysis (ITS2-RFLP), consisting of amplification of the ITS2 region, restriction digestion with BstUI (CG/CG) and restriction fragment length determination by capillary electrophoresis. ITS2-RFLP analysis proved to be most useful for identification of species of the genera Arthroderma, Chrysosporium and Epidermophyton, but could not distinguish between several Trichophyton species. The identification results are in agreement with established and recent taxonomical insights into the dermatophytes; for example, highly related species also had closely related and sometimes difficult-to-discriminate ITS2-RFLP patterns. In some cases, several ITS2-RFLP groups could be distinguished within species, again mostly in agreement with the taxonomic delineations of subspecies and/or genomovars, confirming the relevance of ITS2-RFLP analysis as an identification technique and as a useful taxonomic approach.