Experimental human Trichophyton mentagrophytes infections

Animal model of dermatophytosis

Dermatophytosis is superficial fungal infection caused by dermatophytes that invade the keratinized tissue of humans and animals. Lesions from dermatophytosis exhibit an inflammatory reaction induced to eliminate the invading fungi by using the host's normal immune function. Many scientists have attempted to establish an experimental animal model to elucidate the pathogenesis of human dermatophytosis and evaluate drug efficacy. However, current animal models have several issues. In the present paper, we surveyed reports about the methodology of the dermatophytosis animal model for tinea corporis, tinea pedis, and tinea unguium and discussed future prospects.

Dermatophyte virulence factors: identifying and analyzing genes that may contribute to chronic or acute skin infections

Dermatophytes are prevalent causes of cutaneous mycoses and, unlike many other fungal pathogens, are able to cause disease in immunocompetent individuals. They infect keratinized tissue such as skin, hair, and nails, resulting in tinea infections, including ringworm. Little is known about the molecular mechanisms that underlie the ability of these organisms to establish and maintain infection. The recent availability of genome sequence information and improved genetic manipulation have enabled researchers to begin to identify and study the role of virulence factors of dermatophytes. This paper will summarize our current understanding of dermatophyte virulence factors and discuss future directions for identifying and testing virulence factors.

Neonatal kerion Celsi: report of three cases

Tinea capitis is a fungal infection caused by dermatophytes, frequent in children but uncommon in the neonatal period. Kerion Celsi is the inflammatory manifestation of tinea capitis secondary to host immunologic responses and its occurrence in newborns is extremely infrequent. We describe three neonates with the diagnosis of kerion Celsi. The isolated dermatophytes were Trichophyton mentagrophytes var. mentagrophytes in two patients and Trichophyton rubrum in the third. Both patients with T. mentagrophytes referred an indirect contact with rabbits and were successfully treated with systemic antifungal (griseofulvin and fluconazole). The patient with T. rubrum had a father with a tinea manuum and both received just topical antimycotic treatment.

Topical griseofulvin in the treatment of dermatophytoses

Whether griseofulvin, which pioneered oral antifungal therapy, works topically has long been an open question. The effectiveness of a 1% griseofulvin spray formulation and the vehicle alone against experimentally induced Trichophyton mentagrophytes lesions on the forearms of 16 healthy volunteers and in the treatment of 100 tinea pedis patients (various dermatophytes) was evaluated in a double-blind study. After treatment of the 58 induced lesions twice daily for 14 days with topical griseofulvin (28) or placebo (30), 89% of lesions receiving griseofulvin were mycologically negative compared with 30% in the placebo group (P < 0.0001). In the tinea pedis patients who applied medication once daily for 4 weeks the mycological cure was 79.2% on the fourth week and 80.9% 2 weeks post-treatment. Resurgence of dermatophytes quickly followed the end of treatment in the placebo group only, which had a mycological cure rate of 34% (week 6). Administration of a topical formulation of griseofulvin thus may be an effective treatment for interdigital dermatophyte infections.

Simplified experimental human dermatophytosis model

The authors have improved and simplified previous methods for producing localized mycotic skin infections in an attempt to compare topical antifungal agents for their bioequivalency. Healthy human volunteers who had negative results for commercial, purified Trichophyton antigen (Trichophytin) were inoculated with Trichophyton mentagrophytes on two sites on each forearm in a randomized study designed to compare the antifungal activities of two ciclopirox olamine formulations. The lesions, easily induced by the authors' method, were localized and did not spread under the occlusive dressings. Infections established at the four sites on 26 subjects were treated twice daily for 14 days with the two active drug formulations and their vehicles. There were no significant differences in culture-documented cure rates or alleviation of clinical signs and symptoms between ciclopirox olamine lotion and cream. Each drug was significantly better than its vehicle. The authors' method seems to be effective and suitable for therapeutic studies.

Antifungal activity of ovotransferrin towards genus Candida

The inhibiting activity of ovotransferrin was tested towards different species belonging to genus Candida. Of one hundred strains tested, only C. krusei showed a noticeable resistance, while the other species appeared to be more sensitive than bacteria to the action of ovotransferrin. The influence of anions, such as bicarbonate and citrate, on the inhibiting activity of ovotransferrin was also investigated. Moreover it was observed that iron saturated ovotransferrin retained its activity, thus suggesting an interaction between the protein and Candida cells.

Monitoring of filamentous fungal growth by in situ microspectrophotometry, fragmented mycelium absorbance density, and 14C incorporation: alternatives to mycelial dry weight

Monitoring of filamentous fungal growth by spectrophotometry is generally considered not feasible. This report describes the monitoring of growth of the filamentous fungi Trichophyton mentagrophytes, Rhizopus oryzae, and Sporothrix schenckii in broth by two new spectrophotometric methods and by 14C incorporation from [U-14C]glucose. Microcultures (200 microliter) were prepared in 96-well, flat-bottom microtiter trays, and macrocultures (4 ml) were prepared in glass vials proportionally scaled up from microcultures. Mycelium accumulation in microcultures was measured without terminating the cultures by in situ microspectrophotometry. Accumulation in macrocultures was monitored by uniformly fragmenting the mycelium with a Broeck tissue grinder and by measuring absorbance density in plastic cuvettes with a dual-beam spectrophotometer. Absorbance measurements were found to increase linearly with mycelial weight. In situ absorbance correlated with absorbance density of fragmented mycelium, indicating that both methods monitored growth equivalently. Both defined lag-, exponential-, and stationary-growth phases. Increases in 14C incorporation, absorbance, and mycelial dry weight were kinetically identical for macrocultures and microcultures of T. mentagrophytes. For R. oryzae and S. schenckii, with the exception of R. oryzae growing in microcultures, incorporation of 14C also defined lag, exponential, and stationary growth after selection of the appropriate isotope-specific activity. This incorporation correlated directly with absorbance. We conclude that in situ microspectrophotometry, fragmented mycelium absorbance density, and, to a lesser extent, 14C incorporation can be used to effectively monitor filamentous fungal growth.

Tinea capitis in Philadelphia

From 1962 to 1979, there was a dramatic change in tinea capitis infections in children in the Philadelphia area. This has been primarily due to the virtual disappearance of tinea capitis due to Microsporum organisms. This dramatic change in a common, highly infectious childhood disease is most likely due to a sudden change in hair styles, particularly in black boys, which prevents infectious spores from reaching the scalp.

Hydroxamate siderophore production by opportunistic and systemic fungal pathogens

It has been suggested that siderophores may function as virulence factors. There have been few studies on production of siderophores by opportunistic and pathogenic fungi. We examined siderophore production by Absidia corymbifera, Aspergillus niger, Rhizopus arrhizus, Rhizopus oryzae, Blastomyces dermatitidis, Histoplasma capsulatum, Sporothrix schenickii, Candida albicans, and Trichophyton mentagrophytes. Fungi were cultured at 37 and 27 degrees C in a chemically defined low-iron media (0.2 microM Fe). Culture supernatants were assayed for siderophores by two nonspecific methods [FeCl3 and Fe(ClO4)3] and three chemically specific assays (catechol, 2,3-dihydroxybenzoate, and hydroxamate). All fungi secreted siderophores. Only siderophores of the hydroxamate type were found. More siderophore was produced at 27 degrees C than at 37 degrees C. The present study adds eight fungi to the list of known siderophore producers and confirms siderophore production by H. capsulatum.

Dermatologic aspects of sports medicine

The skin lies at the interface of the athlete and the sports milieu and is subjected to many sports-related dermatoses. Direct traumatic injuries, such as friction blisters, black heel, piezogenic papules, and traumatic subungual hematomas, occur regularly. Environmental insults such as sunburn, cold-induced injury, and contact dermatitis plague the sportsman. Cutaneous infections such as "athlete's foot," otitis externa, herpes simplex, and warts occur because of a favorable microenvironment, occurring with sweating and occlusion as well as close interpersonal contact. Sports participation may uncover or exacerbate latent dermatoses such as occurs in acne mechanica and exercise-induced anaphylaxis. The sportsman is best served if the physician considers him as an athlete-patient.

The effect of human lymphokine on the growth of Trichophyton mentagrophytes

Lymphokine was tested for fungal growth inhibitory activity against the filamentous fungus Trichophyton mentagrophytes. Human peripheral blood lymphocytes from a donor exhibiting delayed type cutaneous hypersensitivity to a trichophytin skin test were cultured with trichophytin and PHA-P. Culture supernatants were assayed for lymphokine activity using the lymphotoxin sensitive mouse L-929 alpha fibroblast. Lymphocyte activation to PHA-P and trichophytin was confirmed by monitoring 3H-thymidine incorporation. Supernatants from 2-day PHA-P and 6-day trichophytin activated cultures were found to contain potent lymphokine activity. This activity was not diminished by the addition of ferric iron sufficient to saturate the contained transferrin. Supernatants from unstimulated control cultures contained no lymphokine activity. Undiluted lymphokine containing supernatants and nonlymphokine containing control supernatants were evaluated for fungal growth inhibitory activity using a sensitive radiometric growth assay. Iron supplemented supernatants retaining potent lymphokine activity did not inhibit fungal growth. Non-iron supplemented supernatants and fresh medium containing serum inhibited fungal growth. Our data suggest that lymphokine active against mammalian cells is not directly antagonistic to the growth of the filamentous fungus T. mentagrophytes but does not exclude the possibility that activated lymphocytes release a chelator such as transferrin that can inhibit fungal growth.

Filamentous fungal growth assay: correlation between [U-14C] glucose uptake and dry weight determinations

The filamentous fungus Trichophyton mentagrophytes was grown in [U-14C] glucose supplemented nutrient broth. Growth was monitored in 200 microliter microcultures and 5 ml macrocultures by measuring the incorporation of 14C into trichloroacetic acid-insoluble macromolecules and in macrocultures by dry weight determination. Adjustment of the specific activity of the [U-14C] glucose medium supplement from 1080 muCi/mmole to 108 muCi/mmole decreased the rate of isotope uptake and prolonged availability so that growth beyond 36 h could be monitored radiometrically. The dry mycelial weight of the fungus was directly proportional (r = 0.995) to the amount of isotope incorporated. Isotope uptake in microcultures and macrocultures was kinetically identical. These data clearly indicate that the uptake of 14C by T. mentagrophytes can be used to monitor fungal growth accurately in both macrocultures and microcultures.

Interactions of Trichophyton mentagrophytes and micrococci on skin culture

Scanning electron microscopy was used to search for local or limited synthesis of antibiotics by a strain of Trichophyton mentagrophytes. Micrococcus luteus, which was susceptible to penicillin and to the dermatophyte when both were cultured on agar media, displayed morphological alterations of flattened walls, invagination, enlargement, and collapse in skin cultures with the fungus. Penicillinase did not neutralize these effects. A control strain of Staphylococcus spp with poor sensitivity to penicillin was resistant to the dermatophyte in all test systems. T. mentagrophytes showed positive tropism to the bacteria. Regional variation in fungal germination and antibiotic production, the limited yield of antibiotics, and the pattern of dermatophyte growth and alteration of bacterial morphology demonstrated the significant influence of microenvironment on antibiosis.

Effect of occlusion on Trichophyton mentagrophytes infections in guinea pigs

The effect of occlusion and griseofulvin on the duration and severity of acute dermatophytosis was assessed in guinea pigs. Sixty guinea pigs given standard Trichophyton mentagrophytes infections were divided into 5 groups: (A) control, (B) intermittent wet occlusion, (C) continuous-wet occlusion, (D) griseofulvin, (E) griseofulvin-continuous-wet occlusion. Lesions were largest in the control group, smallest in the griseofulvin-continuous-occlusion group, and of intermediate area in the other groups. The degree of inflammation and alopecia was not affected by occlusion, but was markedly reduced or eliminated with griseofulvin. Healing of the lesions occurred more rapidly in the griseofulvin-continuous-occlusion group than in any other group. This study suggests that either occlusion of the inoculated site or oral griseofulvin markedly reduces the expected area of the fungal lesion, and occlusion together with griseofulvin shortens the duration of the lesion.

Occlusion, carbon dioxide, and fungal skin infections

Occlusion of the skin renders it susceptible to acute fungal skin infections (dermatophytosis and candidiasis). Occlusion also raised carbon-dioxide (CO2) tensions at the skin's surface. Comparable CO2 tnesions have a pronounced effect on the morphology and metabolism of dermatophytes in vitro. It is postulated that dermatophyte conida and hyphae produce infective units under conditions of raised CO2 tensions, and that occlusion of the skin produces the concentrations of CO2 required for the conversion. Fungal skin infections might be prevented or controlled by interference with the action of CO2 or by prevention of its accumulation under wet, occlusive clothing.

A quantitative dermatophyte infection model in the guinea pig--a parallel to the quantitated human infection model

A method is described for inducing quantitative dermatophyte infections in guinea pigs. This model is unique in that the epidermis in the infection site is not traumatized nor is it epilated. One hundred spore-inocula of Trichophyton mentagrophytes var. granulosum ATCC number 18748 induced infections in 85% of tested guinea pigs. The course of these infections in guinea pigs that had not had a previous infection (inexperienced) and those that had (experienced) paralleled that seen in experimental infections of human volunteers.

An automated radiometric microassay of fungal growth: quantitation of growth of T. mentagrophytes

An automated radiometric microassay of the growth of Trichophyton mentagrophytes and other filamentous fungi is described. The assay is based upon the incorporation of 14C(U) glucose into the organism. Fractionation studies indicate that 73% of the label is found in trichloroacetic acid-insoluble macromolecular components of the mycelium. Incorporation of label directly correlated with growth as estimated by visual scoring of turbidity and as recorded in photomicrographs. Incorporation of 14C(U) glucose delineated a lag, exponential and stationary or plateau phase of growth. These phases could be completely inhibited by the antifungal agent tolnaftate. It was concluded that the growth of filamentous fungi can be successfully monitored by the radiometric method described. Moreover, this method is sensitive, accurate, reproducible, rapid and free of the variability inherent in many traditional estimates growth.

Effect of experimental dermatophyte infection on cutaneous flora

The cutaneous aerobic bacterial flora was monitored during the course of experimental dermatiphyte (ringworm) infections on the forearms of 9 volunteers. Micrococcaceae were identified by the new Baird-Parker classification with the aid of a replica-plating technique. There were significant differences in total populations but not in kinds of flora compared with control (opposite) forearms. The proportion of penicillin-resistant microorganisms, however increased the infection, to a degree which varied as to individual. All coccal groups were affected; resistant flora diminished when the fungus was no longer DETECTED. Staphylococci were more frequently isolated than micrococci on the infected areas, but Staphylococcus aureus was not found. Trends toward hierarchies in persistance and quantities IV were observed among the flora, with Staphylococcus subgroups II and dominating the infected sites. On both areas almost all diphtheroids were nonfluorescent, lipophilic, and lipolytic. One subject consistently carried Bacillus firmus; another's normal microbiota contained Alcaligenes faecalis.