Tinea unguium onychomycosis caused by dermatophytes: a ten-year (2005-2014) retrospective study in a tertiary hospital in Singapore.

INTRODUCTION: Tinea unguium is a common nail infection. We conducted a retrospective ten-year study of the patient demographics and species distribution of dermatophytes causing tinea unguium in a tertiary hospital from Singapore. METHODS: Results of fungal nail cultures were retrieved from our hospital's microbiology department. Samples from nail scrapings and clippings were inoculated onto agar plates (Sabouraud dextrose agar with chloramphenicol and Mycosel agar). Nail specimens that grew dermatophytes were included in the study. RESULTS: Overall, 229 (male: n = 164, 71.6%; female: n = 65, 28.4%) nail specimens grew dermatophytes. Mean patient age was 58 (range 18-93) years. A majority of specimens came from patients aged over 50 years (n = 162, 70.7%) and 60-79 years (n = 100, 43.7%). Ethnically, 160 (69.9%) patients were Chinese, 36 (15.7%) Indian, 18 (7.9%) Malay and 15 (6.6%) of other ethnicities. Among dermatophytes isolated were Trichophyton rubrum (n = 93, 40.6%), Trichophyton mentagrophytes (n = 60, 26.2%), unidentified Trichophyton spp. (n = 57, 24.9%), Trichophyton tonsurans (n = 10, 4.4%), Epidermophyton floccosum (n = 5, 2.2%), Trichophyton verrucosum (n = 2, 0.9%), Trichophyton soudanense (n = 1, 0.4%) and Trichophyton violaceum (n = 1, 0.4%). CONCLUSION: A majority of isolates were from elderly patients. Compared to Singapore's general population, patients of Indian and other ethnicities were over-represented for tinea unguium when compared to Chinese and Malay patients. Trichophyton rubrum was the most common dermatophyte isolated, while Trichophyton verrucosum, Trichophyton violaceum and Trichophyton soudanense were rare causes of tinea unguium.

Pathogenesis of Dermatophytosis: Sensing the Host Tissue.

The genera Trichophyton, Microsporum, and Epidermophyton include filamentous fungi that cause dermatophytosis, a superficial infection of the skin, stratum corneum, nail beds, and hair follicles. The ability of dermatophytes to adhere to these substrates and adapt to the host environment is essential for the establishment of infection. Several fungal enzymes and proteins participate in this adaptive response to the environment and to keratin degradation. Transcription factors such as PacC and Hfs1, as well as heat shock proteins, are involved in sensing and adapting to the acidic pH of the skin in the early stages of fungal-host interaction. During dermatophyte growth, with keratin as the sole carbon source, the extracellular pH shifts from acidic to alkaline. This creates an environment in which most of the known keratinolytic proteases exhibit optimal activity. These events culminate in the establishment and maintenance of the infection, which can be chronic or acute depending on the dermatophyte species. This review focuses on these and other molecular aspects of the dermatophyte-host interaction.

Haemolytic and co-haemolytic (CAMP-like) activity in dermatophytes.

Dermatophytes are some of the most common fungal pathogens in both humans and animals. These fungi release enzymes (e.g., keratinases) that play roles in their pathogenesis. Little is known about their haemolytic and co-haemolytic (CAMP-like) activities; however, in bacteria, these components play significant roles in pathogenesis. This study characterised these two factors in 45 dermatophyte strains (representing the genera Arthroderma, Epidermophyton, Microsporum and Trichophyton) using Columbia agar (CA) supplemented with 5% bovine, ovine and equine erythrocytes. Haemolysis was best observed on CA supplemented with ovine erythrocytes followed by equine and bovine erythrocytes, while CAMP-like reactions occurred using bovine and ovine but not equine erythrocytes. Haemolytic and CAMP-like activities were best observed using ovine and bovine erythrocytes in CA in 44 and 38 strains at 7 and 3 days respectively. Most dermatophytes recovered from both symptomatic and asymptomatic lesions had haemolytic and CAMP-like activities. We suggest that the haemolytic and CAMP-like activities are not correlated with ecological characteristics, isolation sites or clinical manifestations of dermatophytic fungi. We also believe that this study has the potential to contribute to the existing literature on dermatophytes and dermatophyte pathogenesis.

Tiña corporis y tiña capitis / Tinea corporis and tinea capitis

La tiña es una infección de la piel, piel cabelluda, uñas o pelo causada por hongos dermatofíticos que invaden el estrato corneo y usan la queratina como nutriente. Existen tres géneros de dermatofitos: Trichophyton, Epidermophyton y Microspurum.

[Exoenzymes of dermatophytes isolated from acute and chronic tinea]. / Exoenzimas de dermatofitos aislados de tiñas agudas y crónicas.

The presence of five enzymes (deoxyribonuclease, elastase, lipase, caseinase and hemolysin) in 76 strains of dermatophytes 47 of Trichophyton rubrum, 10 of T. mentagrophytes, five of T. tonsurans, 10 of Microsporum canis and four of Epidermophyton floccosum) isolated from 30 cases of acute dermatophytosis and from 46 chronic ones was determined by a qualitative plate assay; in the same way, the presence of these five enzymes with the acute and chronic dermatophytosis was correlated. It was observed that three of the enzymes were produced by the strains with a meaningful frequency; deoxyribonuclease was produced by 84.2% of the strains; elastase by 82.9%; and lipase by 65.8%. In T. rubrum the DNase was produced in 100% of strains. DNase and elastase were related to fungi which caused acute or chronic dermatophytosis in 93.3/78.2% and 96.6/74% respectively. On the other hand, lipase was present in 76% of strains, the ones that caused the chronic infections.

Further observations on the keratinolytic activity of strains of the genus Epidermophyton.

The ability of 17 strains of Epidermophyton to perforate hair in vitro using the Ajello & Georg's test procedure and a modification of Lu's method has been studied. Following the Ajello & Georg's test procedure only E. stockdaleae perforated hair. Sporadically some strains of E. floccosum perforated horse hair. We noted as well unusual perforations originated from inside to outside of the hair. By the other technique, all strains, excepting E. floccosum var. nigricans in child hair, perforated hair. E. floccosum showed these perforations later than E. stockdaleae.

Experimental dermatophytoses produced by E. floccosum in guinea pigs.

Experimental dermatophytoses were tested in guinea pigs by 17 strains of genus Epidermophyton. Only three strains of E. floccosum produced lesions. These lesions were detected 5-7 d after inoculation, and no crust formation or alopecia was observed. These lesions were also studied using microbiological and histopathological techniques. No infection occurred after cutaneous application of E. floccosum var. nigricans and E. stockdaleae.