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

Evaluation Of The Efficacy Of Fluorescent Staining And Chicago Sky Blue Staining As Methods For Diagnosis Of Dermatophytosis In Hair And Nails

Purpose

Dermatophytes are fungi that cause infections affecting hair, nail, and skin; in nails they cause onychomycosis, while in hair they lead to tinea capitis. Detection of dermatophytes using traditional methods, including potassium hydroxide (KOH) and culture on agar-based media leads to high rates of false-negative results. Here, we investigated more accurate diagnostic techniques, including Chicago sky blue staining and Calcofluor white fluorescent staining and compared them with traditional KOH and culture methods for the diagnosis of fungi causing onychomycosis and tinea capitis.

Patients and methods

This study was conducted using samples from 50 patients with dermatophytosis of the hair or nail. Samples were subjected to all the following laboratory investigations: KOH wet mount, culture on Sabouraud's dextrose agar, Chicago sky blue staining, and Calcofluor white staining. The results of the new diagnostic techniques were compared with those of the traditional methods.

Results

Calcofluor white stain and Chicago sky blue stain for dermatophytosis of hair and nail are more specific and sensitive as compared to traditional diagnostic methods. KOH wet mount is simple, rapid, and inexpensive test but lacks color contrast and gave more false positive (artifacts) and false-negative results as compared to these new stain methods.

Conclusion

Chicago sky blue and Calcofluor white staining are excellent methods for diagnosis of fungal infections, including those that cannot be confirmed using conventional methods.

Comparison of fungal fluorescent staining and ITS rDNA PCR-based sequencing with conventional methods for the diagnosis of onychomycosis

BACKGROUND

The current gold standard for diagnosing onychomycosis is direct microscopic examination and culturing. Fungal culture is a time-consuming procedure, while direct microscopy of potassium hydroxide (KOH) mounts suffers from low sensitivity. More rapid and sensitive methods for the diagnosis of onychomycosis are in high demand.

OBJECTIVE

To establish an effective method for the diagnosis of onychomycosis by assessing the efficacies of fungal fluorescent staining and internal transcribed spacer (ITS) ribosomal DNA (rDNA) polymerase chain reaction (PCR)-based sequencing.

METHODS

A total of 204 clinical specimens from patients with suspected onychomycosis were analysed. The gold standard for a true positive sample was positive by KOH, culturing or both methods. All specimens were also tested by fungal fluorescent staining and ITS rDNA PCR-based sequencing. We compared the detection, sensitivity and specificity for these two methods with conventional methods.

RESULTS

In total, 126 (62%) and 102 (50%) were detected by fluorescent staining and PCR-based sequencing, respectively. According to the conventional diagnostic standard, the sensitivity of fluorescent staining and PCR-based sequencing was 97% and 78%, respectively, and specificities of 89% and 90%, respectively. Use of fluorescence enhanced the sensitivity of direct examination by 12% compared with KOH. PCR-based sequencing increased the sensitivity by 6% compared with culturing.

CONCLUSIONS

Fluorescence microscopy has a higher sensitivity for the detection of fungi in nail specimens compared with KOH and can be used as a rapid screening tool. PCR-based sequencing was faster and more sensitive compared with culture and when used in conjunction with fluorescence microscopy resulted in higher efficiency.

Photodynamic action of protoporphyrin IX derivatives on Trichophyton rubrum

BACKGROUND

Dermatophytes are filamentous keratinophilic fungi. Trichophyton rubrum is a prevalent infectious agent in tineas and other skin diseases. Drug therapy is considered to be limited in the treatment of such infections, mainly due to low accessibility of the drug to the tissue attacked and development of antifungal resistance in these microorganisms. In this context, Photodynamic Therapy is presented as an alternative.

OBJECTIVE

Evaluate, in vitro, the photodynamic activity of four derivatives of Protoporphyrin IX by irradiation with LED 400 nm in T. rubrum.

METHOD

Assays were subjected to irradiation by twelve cycles of ten minutes at five minute intervals.

RESULT

Photodynamic action appeared as effective with total elimination of UFCs from the second irradiation cycle.

CONCLUSION

Studies show that the photodynamic activity on Trichophyton rubrum relates to a suitable embodiment of the photosensitizer, which can be maximized by functionalization of peripheral groups of the porphyrinic ring.

High throughput multiplex-PCR for direct detection and diagnosis of dermatophyte species, Candida albicans and Candida parapsilosis in clinical specimen

We have developed and validated a multiplex-PCR method for detection of dermatophyte spp., Candida albicans and parapsilosis for routine diagnostics. Our m-PCR showed excellent concordance with culture results in 475 clinical samples. Through the rapid diagnosis by our m-PCR, clinicians are able to initiate adequate antimycotic therapy much earlier.

Rapid detection of dermatophytes and Candida albicans in onychomycosis specimens by an oligonucleotide array

Background

Onychomycosis is a fungal infection of nails, leading to the gradual destruction of the nail plate. Treatment of onychomycosis may need long-time oral antifungal therapy that can have potential side effects, thus accurate diagnosis of the disease before treatment is important. Culture for diagnosis of onychomycosis is time-consuming and has high false-negative rates. To expedite the diagnosis, an oligonucleotide array, based on hybridization between immobilized oligonucleotide probes and PCR products, for direct detection of dermatophytes and Candida albicans in clinical specimens was evaluated.

Methods

Species-specific oligonucleotide probes designed from the internal transcribed spacer (ITS) regions of the rRNA gene were immobilized on a nylon membrane. The assay procedures consisted of PCR amplification of the ITS using universal primers, followed by hybridization of the digoxigenin-labeled amplicons to probes on the array. Thirty two nail samples (29 patients) were analyzed by the array, and the results were compared with those obtained by culture. Array-positive but culture-negative samples were confirmed by cloning and re-sequencing of the amplified ITS and by reviewing patient’s clinical data. The total recovery of culture and confirmed array-positive but culture-negative results was considered 100% and was used for performance evaluation of both methods.

Results

Concordant results were obtained in 21 samples (10 positives and 11 negatives) by both methods. Eleven samples were array-positive but culture-negative; among them, 9 samples were considered true positives after discrepant analysis. Comparing with culture, the array had significantly higher sensitivity [100% (95% CI 82.2% −100%) vs 52.6% (28.9% −75.5%), p <0.001] and negative predictive value [100% (71.3% −100%) vs 59.1% (36.4% −79.3%), p <0.05), while no significant differences were observed in specificity (84.6% vs 100%, p =0.48) and positive predictive value (90.5% vs 100%, p =1.0). The whole procedures of the array were about 24 h, whilst results from culture take 1 to 3 weeks.

Conclusions

The array offers an accurate and rapid alternative to culture. Rapid diagnosis can expedite appropriate antifungal treatment of onychomycosis. However, the single site nature of this study conducted at a referral hospital invites caution.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-014-0581-5) contains supplementary material, which is available to authorized users.

Evaluation of PCR for the diagnosis of dermatophytes in nail specimens from patients with suspected onychomycosis

BACKGROUND

Conventional methods for detecting fungi in nail specimens are either nonspecific (microscopy) or insensitive (culture). Recently, PCR has been used to improve sensitivity in detecting the causative fungi in nail specimens from patients with suspected onychomycosis.

AIM

To compare the detection rates of PCR with those of microscopy (with potassium hydroxide; KOH) and culture for dermatophytes in nail specimens from patients with suspected onychomycosis.

METHODS

In total, 120 patients with clinically suspected onychomycosis were recruited, and using a topoisomerase II-based PCR, we compared the detection rate of dermatophytes for the three methods.

RESULTS

KOH microscopy, culture and PCR respectively yielded positive rates of 35 (29.2%), 12 (10%) and 48 (40%), and negative rates of 85 (70.8%), 108 (90%) and 72 (60%). Two culture-positive specimens were not detected by PCR, but PCR picked up 38 specimens missed by culture. Of the 35 specimens that were microscopy-positive, 12 grew dermatophytes and 23 nondermatophytes.

CONCLUSIONS

This study demonstrates that PCR has a higher positive and lower negative rate for detection of dermatophytes compared with KOH microscopy or culture. We suggest that PCR should be used as a complementary method for confirmation of clinically suspected dermatophytic onychomycosis.