Antifungal efficacy of lasers against dermatophytes and yeasts in vitro.

PURPOSE: Approximately 2-13% of the world population suffers from onychomycosis. Recently, lasers have been introduced for treatment. However, no effect was found with in vitro laser irradiation of pathogens on agar plates. This study aimed to investigate the efficacy of laser irradiation against fungi using an alternative in vitro approach. MATERIALS AND METHODS: Lasers of 808, 980 and 1064 nm were used to heat cell culture media and a nail clipping. Trichophyton rubrum. T. interdigitale. Microsporum gypseum. Candida albicans. C. parapsilosis, and C. guilliermondii species were subcultured and subjected to laser treatments (808/980 nm: 9-27 J/cm(2), 6 ms, 12 × 12 or 12 × 50 mm and 1064 nm: 50-240 J/cm(2), 90 ms, 5-10 mm). After irradiation, the fungal elements were transferred onto agar plates using conventional and Drigalski spatulas and were incubated for 6 days. RESULTS: The highest increase in temperature was found using a 980-nm laser with a pulse duration of 6 ms and a fluence of 27 J/cm(2). The histology work-up revealed a dissection of the nail plate from the nail bed tissue after laser irradiation. Growth inhibition was only found for C. guilliermondii and T. interdigitale. All other pathogens presented only reduced growth, and C. albicans growth was unaffected. CONCLUSIONS: This study demonstrates a clear thermal effect for linear scanning 980-nm and long-pulsed 1064-nm laser systems on either nail clippings or cell culture media. Complete pathogen growth impairment was achieved if temperatures were measured above 50 °C. The results for the 1064-nm system were almost comparable to 980 nm results.

UV susceptibility and negative phototropism of dermatophytes.

High doses of ultraviolet radiation (UVR) have well-known inhibitory effects upon dermatophytes. In the present study, the effect of repetitive low doses of UVR on mycelial growth of dermatophytes was tested. Pellets of Trichophyton rubrum, T. mentagrophytes and Microsporum canis were placed between two thin layers of Sabouraud glucose agar. Obverse, reverse or both sides of these 'sandwich' agars were irradiated for 10 days twice daily with 0.13 or 0.17 J cm-2 UVB. To simulate microaerophilic conditions, one or both agar sides were covered by transparent airtight plastic lids. In addition, T. rubrum was also grown as usual on plates of Sabouraud glucose agar without any covering, and irradiated on its obverse side twice daily with UVA (13.5 J cm-2), UVB (0.17, 0.34 or 0.69 J cm-2) or infrared light, or once only with 3.8-15.1 J cm-2 UVB. As a result, thallus diameters of all strains were found to be reduced by repetitive UVB irradiation under both aerobic and microaerophilic growth conditions. T. rubrum was unaffected by infrared irradiation, responded with an increased pigmentation to UVA (13.5 J cm-2 twice daily) and was inhibited by a single dose of 15.1 J cm-2 UVB. Negative phototropism of dermatophytes is a new observation. It may be biologically relevant as a mechanism to evade harmful doses of UVR.

Ultraviolet-mediated antimycotic activity of alpha-terthienyl on Microsporum cookei.

Alpha-terthienyl (alpha-T) in the presence of UV-A irradiation reduced the growth rate of Microsporum cookei. In the dark, alpha-T accumulated in small diffuse vacuoles within the hyphae. After UV-A treatment, alpha-T caused damage to the membranes of the nucleus, mitochondria and endoplasmic reticulum. Plasmolytic and autolytic changes occurred resulting in plasma membrane breakage and cell wall aberrations. UV-A activated alpha-T would appear to target membrane proteins.

In vitro and in vivo photosensitized inactivation of dermatophyte fungi by heterotricyclic dyes.

The ability of three heterotricyclic dyes to photosensitize dermatophyte fungi was studied with Trichophyton mentagrophytes and Microsporum gypseum. In vitro studies showed that methylene blue, neutral red, and proflavine were capable of killing these fungi when used in conjunction with broad-spectrum light. Proflavine, however, killed both fungi most rapidly and was used for further studies. Fungal killing by proflavine plus light was dependent on dye concentration, pH, light wavelength, and light intensity. Based on the in vitro studies, a treatment regimen was developed for in vivo use on experimentally infected animals. When treatment of guinea pigs inoculated with T. mentagrophytes was begun during fungal invasion, lesion formation at inoculated sites was either prevented or substantially reduced. When treatment was begun after lesion formation, however, light-plus-dyed treated sites showed only slightly faster curing than untreated sites.

The formation of macroconidia in dermatophytes following UV irradiation and temperature treatment.

The ability of sterile hyphae of Epidermophyton and Microsporum to produce macroconidia was restored by exposing hyphae to ultra violet irradiation followed by prolonged incubation at 35 degrees C. The four species of Trichophyton used in the present study did not produce macroconidia after such treatments.

Light resistance in geophilic dermatophytes.

The effect of repeated illumination by ultraviolet or visible light on slide cultures of Trichophyton ajelloi and Microporum cookei was studied. Under UV light, germination was inhibited, spores were damaged and destroyed, growth was suppressed and the hyphae were killed. Inhibition was dependent on exposure time and wavelength. Lethal doses for the far UV range were as high as 1 300-1 700 mW sec/cm2 for T. ajelloi and 2 300 mW sec/cm2 for M. cookei. The same effect was caused by the complete UV region but the far UV range was most effective. One exposure, however long, was not sufficient to kill the inoculum but this was effected by smaller doses when repeated 4 times at daily intervals. Under visible light, germination of the spores and growth of the young hyphae were inhibited. Depending on the exposure time and wavelength used, inhibition of 8 to 76% of controls grown in darkness were noted. The inhibition degree was increased up to lethality when the mycelium was sensitized by means of eosin. The coefficient of variation increased regularly up to very high values following exposures to sublethal doses of light...