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Trichophyton rubrum

trichophyton rubrum, trichophyton rubrum treatment
Trichophyton rubrum is a dermatophytic fungus in the phylum Ascomycota, class Euascomycetes It is an exclusively clonal,1 anthropophilic saprotroph that colonizes the upper layers of dead skin, and is the most common cause of athlete's foot, fungal infection of nail, jock itch, and ringworm worldwide2 Trichophyton rubrum was first described by Malmsten in 1845 and is currently considered to be a complex of species that comprises multiple, geographically patterned morphotypes, several of which have been formally described as distinct taxa, including T raubitschekii, T gourvilii, T megninii and T soudanense345

Contents

  • 1 Growth and morphology
    • 11 Variants
  • 2 Diagnostic tests
  • 3 Pathology
    • 31 Foot
    • 32 Hand
    • 33 Groin
    • 34 Nail
  • 4 Epidemiology
  • 5 Transmission
  • 6 Treatment
  • 7 References

Growth and morphologyedit

Bottom view of a Sabouraud agar plate with a colony of Trichophyton rubrum var rodhainii

Typical isolates of T rubrum are white and cottony on the surface The colony underside is usually red, although some isolates appear more yellowish and others more brownish6 Trichophyton rubrum grows slowly in culture with sparse production of teardrop or peg-shaped microconidia laterally on fertile hyphae Macroconidia, when present, are smooth-walled and narrowly club-shaped, although most isolates lack macroconidia6 Growth is inhibited in the presence of certain sulfur-, nitrogen- and phosphorus-containing compounds Isolates of T rubrum are known to produce penicillin in vitro and in vivo7

Variantsedit

Strains of T rubrum form two distinct biogeographical subpopulations One is largely restricted to parts of Africa and southern Asia, while the other consists of a population that has spread around the world Isolates of the Afro-Asiatic subpopulation most commonly manifest clinically as tinea corporis and tinea capitis4 In contrast, the globally-distributed subpopulation manifests predominantly in tinea pedis and tinea unguium4 Different members of the T rubrum complex are endemic to different regions; isolates previously referred to T megninii originate from Portugal, while T soudanense and T gourvilii are found in Sub-Saharan Africa All species included in the T rubrum complex are "–" mating type with the exception of T megninii which represents the "+" mating type and is auxotrophic for L-histidine4 The mating type identity of T soudanense remains unknown6 Trichophyton raubitschekii, which is common from northwestern India and southeast Asia as well as parts of West Africa, is characterized by strongly granular colonies and is the only variant in the complex that reliably produces urease6

Diagnostic testsedit

Colonies of T rubrum isolated from toenail left-right: Primary isolation from scrapings on Sabouraud's dextrose agar with cycloheximide, chloramphenicol and gentamicin 14 d; Greenish colonies on Littman Oxgall agar 14 d; Restricted, red colony without pH change on Bromocresol Purple Milk Solids Glucose agar 10 d Colonies of T mentagrophytes left, T rubrum center and T violaceum right showing differential responses on Bromocresol Purple Milk Solids Glucose agar 7 d T mentagrophytes shows unrestricted growth with alkaline purple colour change, T rubrum shows restricted growth with no pH change, and T violaceum produces weak growth accompanied by clearing of the milk solids and a purple colour change

As a preliminary test indicating infection, plucked hairs and skin and nail scrapings can be directly viewed under a microscope for detection of fungal elements T rubrum cannot be distinguished from other dermatophytes in this direct examination It can distinguished in vitro from other dermatophytes by means of characteristic micromorphology in culture, usually consisting of small, tear-drop-shaped microconidia, as well as its usual blood-red colony reverse pigmentation on most growth media In addition, the Bromocresol purple BCP milk solid glucose agar test can be used to distinguish it Different Trichophyton species release different amounts of ammonium ion, altering the pH of this medium In this test, medium supporting T rubrum remains sky blue, indicating neutral pH, until 7 to 10 days after inoculation68 In primary outgrowth on Sabouraud dextrose agar with cycloheximide and antibacterials, contaminating organisms may cause confusion, as T rubrum colonies deprived of glucose by competing contaminants may grow without forming the species' distinctive red pigment6 Both antibiotic-resistant bacteria and saprotrophic fungi may outcompete T rubrum for glucose if they contaminate the sample Red pigment production can be restored in such contaminated isolates using casamino acids erythritol albumin agar CEA6 T rubrum cultures can be isolated on both cycloheximide-containing media and cycloheximide-free media The latter are conventionally used for the detection of nail infections caused by non-dermatophytes such as Neoscytalidium dimidiatum6 A skin test is ineffective in diagnosing active infection and often yields false negative results9

Pathologyedit

Trichophyton rubrum is rarely isolated from animals6 In humans, men are more often infected than women10 Infections can manifest as both chronic and acute forms8 Typically T rubrum infections are restricted to the upper layers of the epidermis; however, deeper infections are possible11 Approximately 80–93% of chronic dermatophyte infections in many parts of the developed world are thought to be caused by T rubrum including cases of tinea pedis, tinea unguium, tinea manuum, tinea cruris, and tinea corporis, as well as some cases of tinea barbae4 Trichophyton rubrum has also been known to cause folliculitis in which case it is characterized by fungal element in follicles and foreign body giant cells in the dermis8 A T rubrum infection may also form a granuloma Extensive granuloma formations may occur in patients with immune deficiencies eg Cushing syndrome Immunodeficient neonates are susceptible to systemic T rubrum infection8

Trichophyton rubrum infections do not elicit strong inflammatory responses, as this agent suppresses cellular immune responses involving lymphocytes particularly T cells8 Mannan, a component of the fungal cell wall, can also suppress immune responses, although the mechanism of action remains unknown9 Trichophyton rubrum infection has been associated with the induction of an id reaction in which an infection in one part of the body induces an immune response in the form of a sterile rash at a remote site6 The most common clinical forms of T rubrum infection are described below

Footedit

Main article: Tinea pedis

Trichophyton rubrum is one of the most common causes of chronic tinea pedis commonly known as athlete's foot10 Chronic infections of tinea pedis result in moccasin foot, in which the entire foot forms white scaly patches and infections usually affect both feet8 Individuals with tinea pedis are likely to have infection at multiple sites10 Infections can be spontaneously cured or controlled by topical antifungal treatment Although T rubrum tinea pedis in children is extremely rare, it has been reported in children as young as two years of age11

Handedit

Main article: Tinea manuum

Tinea manuum is commonly caused by T rubrum and is characterized by unilateral infections of the palm of the hand8

Groinedit

Main article: Tinea cruris

Along with E floccosum, T rubrum is the most common cause of this disease, also known as 'jock itch' Infections cause reddish brown lesions mainly on the upper thighs and trunk, that are border by raised edge8

Nailedit

Main article: Onychomycosis

Once considered a rare causative agent,10 T rubrum is now the most common cause of invasive fungal nail disease called onychomycosis or tinea unguium8 Nail invasion by T rubrum tends to be restricted to the underside of the nail plate and is characterized by the formation of white plaques on the lunula that can spread to the entire nail The nail often thickens and becomes brittle, turns brown or black11 Infections by T rubrum are frequently chronic, remaining limited to the nails of only one or two digits for many years without progression10 Spontaneous cure is rare10 These infections are usually unresponsive to topical treatments and respond only to systemic therapy12 Although it is most frequently seen in adults, T rubrum nail infections have been recorded in children10

Epidemiologyedit

It is thought that Trichophyton rubrum evolved from a zoophilic ancestor, establishing itself ultimately as an exclusive agent of dermatophytosis on human hosts Genetic analyses of T rubrum have revealed the presence of heat shock proteins, transporters, metabolic enzymes and a system of up-regulation of key enzymes in the glyoxylate cycle2 The species secretes more than 20 different proteases, including exopeptidases and endopeptidases11 These proteases allow T rubrum to digest human keratin, collagen and elastin; they have an optimum pH of 8 and are calcium dependent11 Although T rubrum shares phylogenetic affiliations with other dermatophytes, it has a distinctive protein regulation system

Transmissionedit

This species has a propensity to infect glabrous hairless skin and is only exceptionally known from other sites11 Transmission occurs via infected towels, linens, clothing contributing factors are high humidity, heat, perspiration, diabetes mellitus, obesity, friction from clothes10 Infection can be avoided by lifestyle and hygiene modifications such as avoiding walking barefoot on damp floors particularly in communal areas10

Treatmentedit

Treatment depends on the locus and severity of infection For tinea pedis, many antifungal creams such as miconazole nitrate, clotrimazole, tolnaftate a synthetic thiocarbamate, terbinafine hydrochloride, butenafine hydrochloride and undecylenic acid are effective For more severe or complicated infections, oral ketoconazole was historically shown to be an effective treatment for T rubrum infections but is no longer used for this indication due to the risk of liver damage as a side effect13 Oral terbinafine, itraconazole or fluconazole have all been shown to be safer, effective treatments Terbinafine and naftifine topical creams have been successfully treated tinea cruris and tinea corporis caused by T rubrum12 Trichophyton rubrum infections have been found to be susceptible to photodynamic treatment,14 laser irradiation,15 and photoactivation of rose bengal dye by green laser light16

Tinea unguium presents a much greater therapeutic challenge as topical creams do not penetrate the nail bed Historically, systemic griseofulvin treatment showed improvements in some patients with tinea unguium; however, failure was common even in lengthy treatment courses eg, > 1 yr Current treatment modalities include oral terbinafine, oral itraconazole, and intermittent "pulse therapy" with oral itraconazole1718 Fingernail infections can be treated in 6–8 weeks while toenail infections may take up to 12 weeks to achieve cure10 Topical treatment by occlusive dressing combining 20% urea paste with 2% tolnaftate have also shown promise in softening the nail plate to promote penetration of the antifungal agent to the nail bed10

Referencesedit

  1. ^ Gräser, Y; Kühnisch, J; Presber, W 1999 "Molecular markers reveal exclusively clonal reproduction in Trichophyton rubrum" Journal of clinical microbiology 37 11: 3713–7 PMC 85735  PMID 10523582 
  2. ^ a b Zaugg, C; Monod, M; Weber, J; Harshman, K; Pradervand, S; Thomas, J; Bueno, M; Giddey, K; Staib, P 2009 "Gene expression profiling in the human pathogenic dermatophyte Trichophyton rubrum during growth on proteins" Eukaryotic cell 8 2: 241–50 PMC 2643602  PMID 19098130 doi:101128/EC00208-08 
  3. ^ William Williams, The Principles and Practice of Veterinary Surgery, p734, WR Jenkins, 1894, from the collection of the University of California
  4. ^ a b c d e Gräser, Y; Scott, J; Summerbell, R 2008 "The new species concept in dermatophytes-a polyphasic approach" Mycopathologia 166 5–6: 239–56 PMID 18478366 doi:101007/s11046-008-9099-y 
  5. ^ Makimura, Koichi; Tamura, Y; Mochizuki, T; Hasegawa, A; Tajiri, Y; Hanazawa, R; Uchida, K; Saito, H; Yamaguchi, H 1999 "Phylogenetic Classification and Species Identification of Dermatophyte Strains Based on DNA Sequences of Nuclear Ribosomal Internal Transcribed Spacer 1 Regions" Clinical Mycology 37: 920–924 PMC 88625  PMID 10074502 
  6. ^ a b c d e f g h i j Kane, Julius 1997 Laboratory handbook of dermatophytes : a clinical guide and laboratory handbook of dermatophytes and other filamentous fungi from skin, hair, and nails Belmont, CA: Star Pub ISBN 978-0898631579 
  7. ^ Youssef, N; Wyborn, CH; Holt, G March 1978 "Antibiotic production by dermatophyte fungi" Journal of general microbiology 105 1: 105–111 PMID 632806 doi:101099/00221287-105-1-105 
  8. ^ a b c d e f g h i Weitzman, I; Summerbell, RC 1995 "The dermatophytes" Clinical Microbiology Reviews 8 2: 240–59 PMC 172857  PMID 7621400 
  9. ^ a b Dahl, MV; Grando, SA 1994 "Chronic dermatophytosis: what is special about Trichophyton rubrum" Advances in dermatology 9: 97–109; discussion 110–1 PMID 8060745 
  10. ^ a b c d e f g h i j k DiSalvo, Edited by Arthur F 1983 Occupational mycoses Philadelphia, Pa: Lea and Febiger ISBN 978-0812108859 CS1 maint: Extra text: authors list link
  11. ^ a b c d e f Kwon-Chung, KJ; Bennett, John E 1992 Medical mycology Philadelphia: Lea & Febiger ISBN 9780812114638 
  12. ^ a b El-Gohary, M; van Zuuren, EJ; Fedorowicz, Z; Burgess, H; Doney, L; Stuart, B; Moore, M; Little, P 2014 "Topical antifungal treatments for tinea cruris and tinea corporis" The Cochrane database of systematic reviews 8: CD009992 PMID 25090020 doi:101002/14651858CD009992pub2 
  13. ^ http://wwwdoctorfungusorg/thefungi/trichophytonphp  Missing or empty |title= help; External link in |website= help; Missing or empty |url= help
  14. ^ Block, PL 1968 "A wire-band splint for immobilizing loose posterior teeth" Journal of periodontology 39 1: 17–8 PMID 5244503 
  15. ^ Vural, Emre; Winfield, Harry L; Shingleton, Alexander W; Horn, Thomas D; Shafirstein, Gal 2007 "The effects of laser irradiation on Trichophyton rubrum growth" Lasers in Medical Science 23 4: 349–353 PMID 17902014 doi:101007/s10103-007-0492-4 
  16. ^ Cronin, L; Moffitt, M; Mawad, D; Morton, OC; Lauto, A; Stack, C June 2014 "An in vitro study of the photodynamic effect of rose bengal on trichophyton rubrum" Journal of biophotonics 7 6: 410–7 PMID 23125143 doi:101002/jbio201200168 
  17. ^ De Doncker, P; Decroix, J; Piérard, GE; Roelant, D; Woestenborghs, R; Jacqmin, P; Odds, F; Heremans, A; Dockx, P; Roseeuw, D January 1996 "Antifungal pulse therapy for onychomycosis A pharmacokinetic and pharmacodynamic investigation of monthly cycles of 1-week pulse therapy with itraconazole" Archives of dermatology 132 1: 34–41 PMID 8546481 doi:101001/archderm132134 
  18. ^ Gupta, AK; Daigle, D; Paquet, M 17 July 2014 "Therapies for Onychomycosis: A Systematic Review and Network Meta-Analysis of Mycological Cure" Journal of the American Podiatric Medical Association 105: 140717071850003 PMID 25032982 doi:107547/13-1101 

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