dermatophytosis , one of the most common infectious diseases in the world , can be caused by dermatophyte fungal species of the genera trichophyton , microsporum and epidermophyton . onychomycosis is a fungal infection of the nails , which may be caused by many types of fungi , other dermatophytes or yeast species ( 1 ) . treatment of onychomycosis is a challenge and infections are typically more severe and difficult to treat in toenails than in fingernails ( 1 ) . treatment requires long - term therapy with oral antifungal medication ( with the cure rates ranging from 48% to 76% ) which may have side effects , and/or topical agents such as ciclopirox ( 34% cure rate ) ( 2 , 3 ) . oral therapies ( terbinafine , itraconazole ) provide access to the nail bed and matrix and are also used to treat concomitant skin infections such as tinea pedis . to prevent side effects prior to and periodically during oral therapy , liver function the newer imidazoles may lead to a higher cure rate ( 4 ) , but these drugs are considerably more expensive than routine treatments . topical therapies are associated with low rates of adverse events and mild localized reactions at the application site , but due to inadequate penetration , especially when the nails are thick , their efficacy is limited . uv radiation induces dna damage leading to inactivation of the pathogenic fungus commonly measured by viability count . uv - a with long wavelength ( 315 - 400 nm ) rays has a slow effect on the skin and is poorly absorbed by the ozone layer . this ray is 1,000 times more common than uv - b with the middle - range of 290 - 320 nm that causes visible damage , commonly observed as redness and blistering and are a major cause of sunburn and skin cancer ( 5 ) . uv - c with wavelengths less than 290 nm ( 100 - 280 nm ) is the shortest and has the highest uv energy . it is filtered by the ozone layer ; these wavelengths do not reach the earth surface and do not penetrate the atmosphere . thus , people are exposed to large doses of uv - a throughout their life , but uv - b rays do not penetrate glass ( 5 ) . high doses of uv - a and uv - b radiation have significant inhibitory effects on dermatophytes ( 6 ) . the antibacterial activity of uv - c radiation reduces the number of bacteria on environmental surfaces and vegetative bacteria including mycobacterium tuberculosis , viruses and fungi ( 7 , 8) . the current study aimed to investigate the fungicidal effect of uv radiation on the growth of dermatophytes isolated from nails , considering the low efficacy of current treatment options and ease of exposing nails to uv light . the sample comprised all the patients referred to the dermatology clinic ( shahid faghihi hospital , shiraz university of medical sciences , iran ) with suspected onychomycosis . the inclusion criteria were clinical manifestations such as distal or proximal sub ungula onychomycosis , white superficial onychomycosis , pitting , paronychia , onycholysis and nail plate discoloration . all diagnoses were confirmed by the mycology laboratory of shahid faghihi hospital , shiraz university of medical sciences , iran . since this procedure was part of the patients usual treatment protocol , informed consent for research purposes was not specifically sought . fragments of nail plate and nail bed scrapes were inoculated onto sabouraud dextrose agar ( sda ) ( merck , germany ) with the antimicrobials cycloheximide ( sigma - aldrich , germany ) and chloramphenicol ( merck , germany ) ( 9 ) , and incubated at 30c for 14 days . isolated species were identified by macroscopic examination of colony morphology ( size , color of the colonies from the top and bottom of the plate , and growth rate ) . microscopic examinations were performed to identify dermatophyte species using lacto phenol - cotton blue and diagnostic methods such as growth on trichophyton agar media ( quelab , uk ) and rice , and hair perforation test were performed to identify ( 9 ) . to determine the influence of different doses of uv light on the fungicidal effect , colony count and size , and growth rate of the isolated fungi were evaluated under laboratory conditions . two strains of trichophyton mentagrophytes and two strains of t. rubrum were isolated from the patients and used in the current study . trichophyton rubrum type 1 was white and had fluffy colony with pink to burgundy on reverse . type 2 was granular with powdery - velvet , radially folded and pale brown in color and the reverse was dark tan . t. mentagrophyte type 1 was downy , floccose and white in color with the fade yellow on reverse . finally , type 2 was coarsely granular and light buff in color with the buff - tan color on reverse . as in the skin samples from patients , only mycelium can be observed , in the current study mycelial colonies were harvested , suspended in sabouraud dextrose broth ( sdb ) ( merck , germany ) and dispersed to small part suspensions using a sonic dismembrator ( dr . hielscher gmbh , stahnsdorf , germany ) . cell densities of the suspensions were counted in a neubauer hemocytometer ( hausser scientific , horsham , pa , usa ) , and reached 10 pieces / ml . fifty l of suspension was inoculated onto sda to observe macroscopic and microscopic colony characteristics . in each test , a 10 ml aliquot of the dermatophyte suspension was inoculated onto a petri dish . uv - a and uv - b lights were supplied by a waldmann uv801kl apparatus ( waldmann , villingen - schwenningen , germany ) at 470 w , and uv - c light was supplied by an f30t8/gl apparatus ( young deungpo - gu , seoul , south korea ) at 30 w. five different doses of uv light were used : uv - a ( 315 - 400 ) 3 , 6 , 9 , 12 , 15 j / cm , uv - b ( 280 - 315 ) 0.5 , 1 , 1.5 , 2 , 2.5 j / cm and uv - c ( 100 - 280 ) 0.3 , 0.6 , 0.9 , 1.2 , 1.5 j / cm . one positive control without exposure to uv light was cultured in each round with the test samples . this distance is widely used in dental and cosmetic fields to sterilize tools ( 10 ) . in the current study , for uv - a and uv - b radiation , the lamps were utilized in the centers for dermatological diseases in order to obtain some practical implications . since radiation reduces the volume and raises the count because of evaporation , which may lead to errors , the specimen volumes were made up to the primary volume ( 10 ml ) after irradiation , with sdb . for each irradiated specimen , the fungicidal effect of uv was evaluated by preparing five cultures to incubate at 30c under laboratory conditions ; therefore , 75 cultures for each fungus were prepared . colony size , morphology and count , and growth rate of all isolates were checked in the plates every two days and mean values were calculated . since most colony growth occurs during the first 14 days , the results were graphed after this period . all statistical analyses were conducted using microsoft excel software.the current research conformed to the helsinki declaration and local legislation , and was approved by the local ethics committee ( 91 - 5 ) in clinical microbiology research center , shiraz university of medical sciences . in response to the uv treatments , compared with suspension control without irradiation , colony morphology for each dermatophyte remained unchanged , but colony count and size changed depending on the species and type of isolate . of the two t. rubrum isolates ( figure 1 ) , type 1 was less sensitive to uv - a and uv - c , and more sensitive to uv - b . continuous irradiation with the uv - a and uv - b doses used in the study did not completely suppress the growth of the isolates , but higher intensities of uv - c light inhibited the growth of t. rubrum . mean colony counts at different intensities uv - a ( 315 - 400 nm ) , uv - b ( 290 - 320 nm ) and uv - c ( 100 - 280 nm ) . of the two t. mentagrophytes isolates ( figure 2 ) , colony count in type 1 decreased as the dose of all three types of uv radiation increased . however , colony count in t. mentagrophytes type 2 showed different patterns as the dose of uv radiation increased . type 2 strain was slightly responsive to uv - abut compared to control cultures ; there was no significant effect on colony count . neither uv - b nor uv - c decreased the type 2 colony counts at low doses , but higher doses led to decreases in colony counts . mean colony counts at different intensities of uv - a ( 315 - 400 nm ) , uv - b ( 290 - 320 nm ) and uv - c ( 100 - 280 nm ) . according to table 1 , uv - a irradiation led to a slight increase in colony size in the four strains except t. mentagrophytes type 1 , in which colony size increased with the lowest dose of irradiation and significantly decreased with increasing the doses . irradiation with uv - b increased colony size in t. mentagrophytes type 2 , but in type 1 uv ray increased colony size at the lowest dose and decreased colony size with increasing doses . uv - b irradiation decreased colony size in t. rubrum type 2 but had no significant effect on type 1 or either of the two strains of t. mentagrophytes . irradiation with uv - c decreased colony size except for t. mentagrophytes type 2 , in which higher doses increased colony size . values are presented as mean  sd .   values are presented as j / cm . according to obtained data , uv light can affect colony count and size of t. rubrum and t. mentagrophytes in the culture , the two fungal species frequently isolated from patients with onychomycosis . the estimated prevalence of onychomycosis caused by these species ranges from 10 to 21.3% in the general population in australia , the united kingdom and iran ( 11 , 12 ) . this prevalence rate may increase to 30% in specific populations such as people over 70 years old ( 13 - 15 ) . it is challenging to determine the optimal treatment and circumventing drug resistance in pathogenic fungi , including dermatophytes . since the nails and skin are being exposed to sunlight , many photodynamic treatments are developed in dermatologic studies . for example , uv light therapy is investigated in diseases such as scleroderma ( 16 ) and onychomycosis ( 17 ) . the mechanism of uv radiation is the primary photochemical reaction , which damages dna and affects survival and rate of germination ( 18 ) . this molecular change makes the dna unstable for essential biological processes such as transcription and replication . as a rule , the simpler the microorganism is in anatomical terms , the more easily it is inactivated by uv radiation . this is why viruses and prokaryotic cells such as bacteria are more easily destroyed than a complex of microorganisms such as eukaryotic cells , yeasts and vegetative fungi . in particular , fungal spores in which the dna is protected by a concentrated cytoplasm and pigmented cell wall some data suggest that solar uv radiation can inhibit the growth of fungi on the soil surface in the antarctic terrestrial environment ( 19 ) , and has disinfectant effects that can vary depending on the type and dosage of irradiation , condition of the surface and exposure time . the effective exposure time was reported to be 45 minutes for yeast and 75 minutes for mold ( 20 ) . different doses of uv - b light show different effects on the growth of candida albicans . increasing doses of uv - b strongly reduced hyphal growth in this fungus and triggered enhanced blastospore formation ( 21 ) . the mechanism of resistance to uv radiation is not completely known , but intra hyphal growth and recolonization of old cells by new ones were observed in all the strains investigated by gorbushina et al . uv - c radiation affected t. rubrum type 1 : as the dose increased , colony count decreased . irradiation with uv - a and uv - b also decreased the colony count of some strains tested in the current study which was proportional to the dose . this finding may be due to the synthesis of new hyphae through the old hyphae not exposed to irradiation , or may be related to the age of the exposed hyphae ( i.e. recolonization of older hyphae ) in the suspension . trichophyton rubrum is one of the most frequent causal agents in nail infections , and recurrence of the infection and resistance to therapy are the most important limitations to treatment success for this anthropophilic dermatophyte ( 22 ) . this species was unaffected by infrared irradiation , responded with increased pigmentation to uv - a at13.5j / cm twice daily , and was inhibited by a single dose of uv - b at 15.1 j / cm ( 6 ) . growth rates , surface colony color and the texture of colony morphology are different in each strain . the current study compared two strains of t. mentagrophytes . according to figure 2 , uv - a , uv - b and uv - c had similar effects on t. mentagrophytes type 1 , but affecting type 2 strains differently . increasing pigmentation in response to uv - a ( 13.5 j / cm twice daily ) was observed in t. rubrum ( 6 ) . electron microscopy studies showed a marked thickening and blurred contours of the cell walls grown with a brightener effect related to interference by optical brighteners with the formation of normal chitin fibrils and thickening of the cell walls ( 23 ) .   in the present study , increasing doses of uv - a , uv - b and uv - c irradiation increased colony size in t. mentagrophytes type 2 . uv - b irradiation of the skin is particularly well studied , and is accepted as the main cause of skin cancer . the depth of penetration of uv - c radiation into the human skin is very low ; therefore , the risk of skin cancer associated with this type of treatment is low . there are studies which report the treatment of localized infections with multidrug - resistant microorganisms ( 24 ) and subungual onychomycosis ( 25 ) with uv - c light irradiation and favorable responses . as mentioned in these studies , the cases were limited and side effects should be taken into account more carefully . when uv irradiation is used to treat onychomycosis , it is important to minimize exposure by carefully masking the area with adhesive material . in addition , the dose of radiation must be minimized by careful dosimetery calculated with reference to the individual patient s nails , the etiologic agent , and optical properties . if there were enough samples , by using different types and doses of irradiation such as uv - a uv - b and uv - c for every single nail sample separately , the current study could directly examine the effects of radiation on them , but since the volume of samples was low , they were just cultured after the isolation of fungal strains and it was possible to evaluate different types and doses of irradiation in the isolated strains . uv - a , uv - b and uv - c seem to be effective in decreasing colony growth in some prevalent fungi , which caused onychomycosis in the patients . further studies are needed to determine the efficacy of this therapy , identify possible side effects and establish appropriate dosages for the antifungal action of uv radiation therapy .
background : the treatment of onychomycosis is a challenge and infections are typically more severe and difficult to treat in toenails than in fingernails.objectives:the current study aimed to investigate the fungicidal effect of ultraviolet radiation on the growth of dermatophytes isolated from nails.patients and methods : samples from patients with clinical manifestations of onychomycosis were inoculated onto sabouraud dextrose agar and incubated at 30c for 14 days . 
 isolated species were identified by specific laboratory examinations ; uv - a , uv - b , and uv - c light were used to irradiate two strains of trichophyton mentagrophytes and t. rubrum . 
 colony count , size and growth rate of the isolated fungi were evaluated under laboratory conditions.results:trichophyton rubrum type 1 was less sensitive to uv - a and uv - c , and more sensitive to uv - b than type 2 . 
 t. mentagrophytes type 2 was slightly responsive to uv - a therapy , although no decrease in colony count was observed . increased doses of uv - b and uv - c irradiation decreased the counts . 
 the effect of radiation on colony size was dependent on the dose and type of irradiation.conclusions:uv-a , uv - b , and uv - c light seem to be effective in decreasing colony growth of the most prevalent fungi , which caused onychomycosis in the current study samples . 
 further studies are needed to determine the efficacy of ultraviolet light therapy , identify possible side effects , and establish appropriate dosages for the antifungal effect of this therapy .