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Development of a New Dermatophyte-Detection Device using Immunochromatography

Wakamoto H, Miyamoto M

Background: The evaluation method for the diagnosis of tinea unguium is mainly microscopy. New antidermatophyte monoclonal antibody have been developed that recognizes the cell wall polysaccharide antigen of filamentous fungi, including dermatophytes, and applied it to immunochromatography. Some scientists focused on this technology, improved it, and determined that this test method provided useful information for a diagnosis of tinea unguium by analyzing large numbers of clinical specimens. However, these studies were carried out by a tentative method.

Objective: Establishment of the usage of this test strip for clinical use and the certification of the stability during long-term storage.

Methods: Various fungi and bacteria were cultured and extracted by extraction buffer to evaluate the reactivity and measurement range of dermatophytes. Trichophyton rubrum was used as a quality control antigen, and detection limits were set at 0.5 μg/ml as weak positive and set at a 100-fold concentration (50 μg/ml) as strong positive. Nail samples, which had already been identified as positive or negative using the test strips, were randomly selected, cut into fine pieces and mixed. Both positive and negative standard nail samples were prepared.

Results: Positive or negative results were obtained from test lines for 5 to 60 minutes at 1 to 30°C. The detection limits of dried 7 samples of dermatophytes were 0.3 to 3 μg/ml. The results of reactivity showed that 8 of dermatophytes were positive. On the other hand, the test strip did not react to Malassezia or Candida species and bacterial strains. Some of Aspergillus, Penicillium, and Fusarium, which are usually not resident microbiota that inhabit nails in healthy persons, showed a positive reaction. The antifungal agents, terbinafine, griseofulvin, and itraconazole did not affect the results. All 3 lots of the test strips met the standards set by the method of quality control after they were kept in storage at 30°C for up to 22 months.

Conclusion: A newly developed dermatophyte-detection device was easy to use, gave rapid results and high reproducibility, and was stable for 22 months at 30°C.