Onychomycosis (trichophyton mentagrophytes). A scanning electron microscopic observation

Scanning electron microscopy of the nail plate in onychomycosis patients with negative fungal culture

Onychomycosis is a common dermatological problem and can be identified by direct microscopic examination and fungal culture. However, the positive rate of fungal culture is low. This study investigated the application of scanning electron microscopy in the diagnosis of onychomycosis in 20 patients with negative fungal culture. In this study, a routine glutaraldehyde fixation method was used to prepare specimens for electron microscope examination. Results showed that under the scanning electron microscope, significant structural damage was observed in the nail plate in all patients. Hyphaes were seen in 70% of cases. A mixture of scattered hyphaes, pseudohyphaes, and spores was observed in 30% of cases. A mixture of spores and bacteria was observed in 10% of cases. A mixture of hyphaes and bacteria was observed in 20% of cases. The typical hyphae pierced a thin layer or single layer of corneocytes. Hyphaes could be smooth, sleek, and straight with visible separation, or dry, bent, and folded with a smooth surface. The diameter of hyphaes was 1-2 µm. The scattered spores were the main form of spore growth, and the growth of budding spores can be seen attached to the surface of layered armor. Most of the bacteria were gathered in clumps on the ventral surface, especially in grooves. In conclusion, scanning electron microscopy can be used to preliminarily identify the pathogen involved and the degree of damage in cases where onychomycosis is clinically diagnosed, but fungal culture is negative.

An ultrastructural study of Trichophyton rubrum induced onychomycosis

Background

Trichophyton rubrum (T.rubrum) caused onychomycosis is the most common nail fungal disease. The common diagnostic methods are direct microscopic examination and fungal culture. In this study we used scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to study the subungual ultrastructural changes in T. rubrum induced onychomycosis.

Methods

Six outpatients with onychomycosis were recruited and T.rubrum infection was confirmed by fungal culture. Six toenail samples were collected and prepared for SEM characterization. The cultured fugal colonies were prepared for SEM and TEM characterization.

Results

1) SEM showed significant structural damages and the formation of a thin layer or a single layer of keratinocytes in all infected nail plates. Hyphae (piercing or penetrating keratinocytes layers), arthrospores and local bacterial aggregation were observed on the ventral surface of the nail plates. 2) SEM of the cultured fungal colony showed relatively straight, highly branched hyphae and microconidias; TEM showed branching hyphae that were composed of double-layer cell walls. Hyphae had nucleus, mitochondria, liposomes, lysosomes, scattered rough endoplasmic reticulum, myeloid bodies and aggregated ribosomes. There were high-density particles outside the hyphae.

Conclusion

SEM showed a large number of hyphae penetrated the keratinocytes layer, suggesting that T. rubrum can cause severe damage to the stratum corneum. TEM showed the ultrastructural features of T. rubrum-induced infection before treatment.

Human nail plate modifications induced by onychomycosis: implications for topical therapy

PURPOSE

Through the characterisation of the human onchomycotic nail plate this study aimed to inform the design of new topical ungual formulations.

METHODS

The mechanical properties of the human nail were characterised using a Lloyd tensile strength tester. The nail's density was determined via pycnometry and the nail's ultrastructure by electron microscopy. Raman spectroscopy analysed the keratin disulphide bonds within the nail and its permeability properties were assessed by quantifying water and rhodamine uptake.

RESULTS

Chronic in vivo nail plate infection increased human nailplate thickness (healthy 0.49 ± 0.15 mm; diseased 1.20 ± 0.67 mm), but reduced its tensile strength (healthy 63.7 ± 13.4 MPa; diseased 41.7 ± 5.0 MPa) and density (healthy 1.34 ± 0.01 g/cm(3); diseased 1.29 ± 0.00 g/cm(3)). Onchomycosis caused cell-cell separation, without disrupting the nail disulfide bonds or desmosomes. The diseased and healthy nails showed equivalent water uptake profiles, but the rhodamine penetration was 4-fold higher in the diseased nails using a PBS vehicle and 3 -fold higher in an ethanol/PBS vehicle.

CONCLUSIONS

Onchomycotic nails presented a thicker but more porous barrier, and its eroded intracellular matrix rendered the tissue more permeable to topically applied chemicals when an aqueous vehicle was used.

Identification, antifungal susceptibility and scanning electron microscopy of a keratinolytic strain of Rhodotorula mucilaginosa: a primary causative agent of onychomycosis

Onychomycosis is a dermatological problem of high prevalence that mainly affects the hallux toenail. Onychomycosis caused by the yeast Rhodotorula mucilaginosa was identified using colony morphology, light microscopy, urease and carbohydrate metabolism in a 57-year-old immunocompetent patient from Rio de Janeiro, Brazil. High-resolution scanning electron microscopy of nail fragments, processed by a noncoating method, led to the observation with fine detail of the structures of both nail and fungus involved in the infection. Yeasts were mainly found inside grooves in the nail. Budding yeasts presented a spiral pattern of growth and blastoconidia were found in the nail groove region. Keratinase assays and keratin enzymography revealed that this isolate was highly capable of degrading keratin. Antifungal susceptibility tests showed that the fungus was susceptible to low concentrations of amphotericin B and 5-flucytosine and resistant to high concentrations of fluconazole, itraconazole, voriconazole and terbinafine. These findings showed data for the first time concerning the interaction of R. mucilaginosa in toenail infection and suggest that this emerging yeast should also be considered an opportunistic primary causative agent of onychomycosis.

Early events in the invasion of the human nail plate by Trichophyton mentagrophytes

A new in vitro model for the study of nail invasion by dermatophyte fungi was developed. The dermatophyte Trichophyton mentagrophytes, and fragments of finger-nails and toe-nails were used. Arthroconidia were inoculated on the ventral surface of the nails. After 6 h, adherence and germination of arthroconidia was observed. By 16 h, small germ tubes with side branches were evident. At about 24 h, micro-colonies had become established. At 48 h, a mycelium had formed, and at about 72 h most of the nail fragment was covered with fungal growth. Nail penetration occurred from the ventral surface through the intercellular spaces, and with longer incubation all three layers were invaded by arthroconidia growing through channels. Nail invasion occurred in the absence of added nutrients. Dermatophyte fungi appeared to invade the nail by a combination of mechanical and chemical factors. The model provides a substrate to study the pharmacokinetics and bioavailability of new antifungal agents in situ.

Treatment of brittle fingernails and onychoschizia with biotin: scanning electron microscopy

Pathologic hoof changes in horses and swine can be normalized by administration of biotin. This vitamin has been given orally to women with brittle fingernails or onychoschizia. The aim of the study was to test whether the favorable clinical results could be corroborated by scanning electron microscopy. We investigated the distal ends of the fingernails from 32 persons. They were placed into three groups: group A consisted of 10 control subjects with normal nails, group B comprised eight patients with brittle nails studied before and after biotin treatment, and group C was 14 patients with brittle nails in whom the administration of biotin did not coincide exactly with the initial and terminal clipping of the nails. The thickness of the nails in group B increased significantly by 25%. In group C, the increase was 7%. Splitting of the nails were reduced in groups B and C and the irregular cellular arrangement of the dorsal surface of brittle nails became more regular in all nails of group B and in 8 of 11 nails of group C.