08 Pod week 8 - Podiatry week 8 Objectives by hjkuiw354

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									                                                                             9/1/2008




                  Podiatry week 8

         Fungi, some fungal diseases and
                        tif     l
                 some antifungals



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                         Objectives
• Understand the diversity of fungi and their beneficial and pathogenic
  roles
• Describe the biological characteristics of fungi
• Describe the structure of a fungal cell and identify how it differs from
  prokaryotic and mammalian cells
• Describe the structure of the fungal cell wall
• Describe the characteristics of the 3 major groups of fungi
• Describe the characteristics of the filamentous fungi – in particular
  ascomycetes and zygomycetes
• Differentiate septate and non-septate hyphae
• Describe the different methods of formation of asexual spored and
  reproduction in fungi from asexual spores
• Describe the different sexual spores associated with zygomycetes
  and ascomycetes and the sexual life cycles of these types of fungi
• Describe the characteristics of yeasts

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                                 Objectives
•   Describe the major classes of fungal diseases– superficial, cutaneous, subcutaneous, systemic,
    mycotoxicoses
•   Differentiate superficial from cutaneous fungal infections – lesions, causative agents
•   Define dermatophytes and name the 3 genera of fungi grouped together as dermatophytes
•   Describe the nature of tinea, ringworm
•   Briefly indicate the steps used to identify fungi in the laboratory
•   Appreciate the importance of subcutaneous mycoses and how they occur
•   Briefly describe infections associated with Sporothrix schenkii
•   Differentiate systemic mycoses caused by pathogenic fungi from those caused by opportunist
    fungal pathogens
•   Understand the geographic associations of pathogenic fungi]
•   Briefly describe infections associated with Histoplasma capsulatum
•   Understand the importance of Candida albicans as an opportunist pathogen and describe
    infections it causes
•                                                        spp,
    Briefly describe infections caused by Aspergillus spp Cryptococcus neoformans zygomycetes
                                                                           neoformans,
    including Penicillium marneffei
•   Briefly describe non-infectious fungal diseases, particularly mycotoxicoses
•   Describe the anti-fungal activity of disinfectants
•   Describe the sites of action of anti-fungal drugs
•   Describe the modes of action of griseofulvin, polyenes, azoles, allylamines, echinocandins,
    nikkomycin, sordarins


                                                                                                     3




                                         Fungi
• Diverse habitats
                                         water,
   – Some are aquatic – mainly fresh water a few marine
   – Most are terrestrial – soil or on dead plant material
      • Crucial role in mineralisation of organic carbon
   – Many are parasites of terrestrial plants
   – A few are parasitic on animals including humans
      • Generally less important than bacterial or viral
        infections



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                             Alexopoulos et al. (1996) Fig 1.4                             5




             Biological significance of fungi
•   Natural decomposers of organic
    matter – saprophytic
•   Plant pathogens
                  parasites,
     – Obligate parasites species
        dependent eg rusts and
        mildews
     – Facultative parasites eg smut
        fungi
•   Industrial importance
     – Fermentation processes eg
        yeasts in beers, wines
        (Saccharomyces cerevisiae)
     – Antibiotic production eg
        Penicillium notatum (penicillin)
•   Human and animal pathogens –
    superficial and systemic mycoses
                                                    Antibiotics: Penicillin from Penicillium
    & allergies
•   Mycotoxins
•   Research – genetics,                                                                   6
    biochemistry, molecular biology




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      Characteristics of fungi
• Eukaryotes
  Lack hl       h l (distinguishes f
• L k chlorophyl (di ti                    l t
                             i h from plants
  & algae)
• Unicellular to filamentous
• Rigid cell wall
• Spore bearing stages in the life cycle
• Usually reproduce by sexual and asexual
  means
• Insensitive to antibacterial antibiotics
                                                 7




Comparison of fungi and bacteria




                 /www.edison.edu/                8
                                            Table 12.2




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         Fungal Cell (eukaryotic)
http://medocs.ucdavis.edu
                                              Capsule
                                              (polysaccharide)
Mitochondrion
                                                         Wall
                                                           α, β glucan
Golgi-                                                     mannan
body
                                                           chitin
                                                           protein
Glycogen


  Vacuole


         N l
         Nucleus                                                 Microtubules
          pore
          nucleolus                                    Cytoplasmic membrane
          envelope                                     ergosterol

                                                       Ribosomes (80S)

                               Endoplasmic reticulum

                                                                                9




                      http://classes.plantpath.wsu.edu/                         10




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         Fungal metabolism
• Chemoorganotrophs (chemoheterotrophs)
  Simple t iti    l     i     t
• Si l nutritional requirements
• Many species can grow at environmental
  extremes – low pH, high temperatures
  – Common contaminants of food products,
    microbial culture media, most surfaces
• Moulds and yeasts not classified by
  physiological characteristics but by their
  life cycles
                                               11




   Morphological types of fungi
Three major groups
1. Moulds
2. Yeasts
3. Mushrooms

Dimorphic fungi – fungi that have both a
   yeast stage and a mould stage

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                           13




Saccharomyces cerevisiae




                           14




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Ascomycete eg Aspergillus spp




                            15




 Zygomycete – eg Rhizopus




                            16




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                           Basidiomycete




                                                                       17




     Filamentous fungi (moulds)
• Widespread in nature – commonly seen on stale bread, cheese or
  fruit
• Each filament grows mainly at the tip by extension of the terminal
  cell
• Single filament is called a hypha
• Hyphae tend to grow together across a surface to form compact
  tufts (a mycelium)
• Mycelium arises because individual hyphae form branches –
  branches intertwine → compact mat




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                 Fungal hyphae
                                         septate (cross walls present)
• typical hypha is a
  nucleated tube containing
  a cytoplasm
• Cross walls may be
  present (septate hyphae)
  or absent (coenocytic
  hyphae)
• Septate hyphae typically
  have more than one
  nucleus per segment


                                                                  19
                                           coenocytic (no cross walls)




                  Fungal spores
• Aerial hyphae – spores on the aerial branches (conidia)
  – asexual spores
   – Often highly pigmented
   – Resistant to drying
   – Help disperse the fungus to new habitats




                                                                   20




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      Asexual reproduction
    Methods of asexual spore formation:
1. chlamydospores (formed within
    sporangia)
2. conidia (formed naked at tips of
    hyphae)
     yp    )
3. budding (cell division)
4. fragmentation (of mycelium)
                                                 21




          Asexual spores
                         http://medocs.ucdavis.edu




            /




                                                 22




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                                                                     23




                 Sexual spores
• Some fungi also produce sexual spores as a
                     p
  result of sexual reproduction
  – Result of fusion of
     • unicellular gametes or
     • specialised hyphae (gametangia)
     • from the fusion of 2 haploid cells to yield a diploid cell which
       then undergoes meiosis and mitosis to yield individual spores
• The nature of the spore depends on the group of
     g
  fungus
  – Ascospores (Ascomycetes)
  – Basidiospores (Basidiomycetes)
  – Zygospores (Zygomycetes)

                                                                     24




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                Sexual spores
• Sexual spores are
  resistant to drying,
  heating, freezing, and
  some chemical agents
• Not as resistant to heat
  as are bacterial
  endospores
• Either a sexual spore or
  an asexual spore can
  germinate and develop
  into a new hypha and
  mycelium
                                             25




        Zygomycete Life Cycle




                                             26
                      /www.edison.edu/   Figure 12.6




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            Ascomycete Life Cycle




                                                                                 27
                               /www.edison.edu/                              Figure 12.7




                               Yeasts
•   Unicellular fungi - 3-5 µm
•   Mostly classified with Ascomycetes
•   Generally spherical, oval or cylindrical
    G       ll    h i l       l     li d i l
•   Cell division generally takes place by budding
     – A new cell forms as an outgrowth of the old cell; the bud gradually
        enlarges and then separates
•   Under some conditions some yeasts can form filaments (dimorphism)
     – Filamentous phase essential for pathogenicity of Candida albicans




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      Pseudohyphae (filaments) produced by yeasts




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Growth by budding in a yeast




                                                    30




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           Budding yeast
      Cryptococcus neoformans
                           http://medhtocs.ucdavis.edu




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  Fungal infections - myocoses
• For many years considered trivial rather
  th lif threatening
  than life th t i
• In recent years fungal infections have
  become much more important –
  immunocompromised people (transplant
  patients on immunosuppressive drugs,
  leukaemia, other cancer patients,
  diabetics, AIDS

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 Fungal diseases of man & animals
Types of fungal diseases
1.
1 Superficial mycoses
2. Cutaneous mycoses
3. Subcutaneous mycosis
4. Systemic mycoses
5. Mycotoxins

Fungi can be true pathogens or opportunistic
   pathogens.

                                                            33




    Superficial fungal infections
• Pityriasis versicor – caused by Melassezia furfur (a
  yeast)
• Mild infection of the skin – ranging from white or non-
  pigmented (darker-skinned people) through to brown
  (fairer skinned people)
• No inflammatory response – lesions are cosmetic




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                Cutaneous mycoses
•   Tinea or ringworm
•   Caused by fungi called dermatophytes
•   Dermatophytes invade the keratinised layers of the skin (superficial
    epidermis, hair and nails)
•   Most important species are:
     – Microsporum spp
     – Trichophyton spp
     – Epidermophyton spp
•   Dermatophytes differ in ecological niche and preferred site of infection
     – Geophilic - Microsporum gypseum
     – Zoophilic - Microsporum canis (dogs, cats/scalp, smooth skin)
             p p                                     (   ,g     ,
     – Anthropophilic - Epidermophyton floccosum (foot, groin, nail); Trichophyton
                          p        p y                                );     p y
       rubrum (trunk, foot, groin, nail); Microsporum audounii (scalp); Trichophyton
       tonsurans (scalp)
•   Anthropophilic organisms are associated with chronic infections
•   Zoophilic and geophilic organisms are associated with more intense
    inflammatory reactions.


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               Cutaneous infections
• Dermatophyte infections are transmitted by
  p         p                     y
  person-to-person contact or by contact with shed
  skin scales or hair clippings (communal
  showers, sharing hats …)
• Tinea pedis – athlete’s foot
• Tinea corporis – ringworm – anywhere on the
  body
                 j           g
• Tinea cruris – jock itch – groin
• Tinea capitis – scalp infections
• Onchomycosis – infection of the nail (can also
  be caused by other fungi)

                                                                                       36




                                                                                                 18
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 Tinea pedis




                            Tinea pedis


                                          37




Onychomycosis




                                          38
http://medocs.ucdavis.edu/mmi/




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Tinea corporis - Ringworm




                            39




          229




                            40




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         Laboratory diagnosis
• Diagnosis based on direct
  exam of scrapings,
  culture on selective
  media
• Examine for fungal
  hyphae and
  characteristic asexual
  spores –
  macroconidia
• Culture – colonies
  also characteristic
                                41




           Microsporum canis




                                42




                                          21
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          Subcutaneous mycoses
Disease                  Fungus
sporotrichosis           Sporothrix schenkii
 h    bl t i
chromoblastosis          F
                         Fonsecaea, Cladosporium, Phi l h
                                    Cl d     i    Phialophora etc,
                                                               t
phaeohyphomycosis        Cladosporium, Exophiala, Wangiella,
                         Bipolaris, Exserophium, Curvularia, etc,
mycotic mycetoma         Pseudallescheria, Madurella,
                         Acremonium, Exophiala etc.
subcutaneous             Basidiobolus ranarum, Conidiobolus
          i
zygomycosis                     t   Rhi       Mucor, Rhi
                         coronatus; Rhizopus, M      Rhizomucor,
                         Absidia, Saksenaea etc
rhinosporidiosis         Rhinosporidium seeberi
lobomycosis              Loboa loboi

        http://www.mycology.adelaide.edu.au/Mycoses/Subcutaneous/    43




          Subcutaneous mycoses
• Rare in Australia
• Occur when a fungus
  penetrates under the skin &
  establishes an infection
• Usually caused by soil or plant
  fungi
• Introduced when the skin is
  broken or damaged – thorn or
  splinter – gardening
• Sporothrix schenkii
   – lives on wood & plants
   – Dimorphic fungus – mould
      form in environment; yeast
      in tissues
   – Causes a chronic
      granulomatous infection
      that can spread along
      lymphatic system                                               44




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              Systemic mycoses
• Caused by pathogenic fungi or
  opportunistic fungi infecting an
  immunocompromised host
• Tend to be free-living dimorphic soil
  associated
• Diseases causes by pathogenic species
  tend t b       ti t dt      ti l
  t d to be restricted to particular
  geographic areas
   – Many confined to the Americas

                                                           45




  Systemic mycoses – pathogenic
              fungi
Fungus           Disease             Distribution
Bl t
Blastomyces      Blastomycosis
                 Bl t       i        N th A    i
                                     North America
dermatidis
Coccidioides     Coccidioidomycosis Soil; south-west
immitis                             USA; Mexico
Histoplasma      Histoplasmosis      Central & Eastern
capsulatum                           USA; South America;
                                          ;                 ;
                                     Africa; Australia, parts
                                     of East Asia (India &
                                     Malaysia
Paracoccidioides Paracoccidioido-    Soil; Latin America
brasiliensis     mycosis
                                                           46




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                 Histoplasmosis
• Histoplasma capsulatum has been
       t d in Australia
  reported i A t li
  – Infections more common in USA (Mississippi -
    Ohio river valley)
  – Associated with inhalation of dust from bat
    droppings in caves
  – Mycotic infection of the RE system
  – 95% cases inapparent or benign
  – 5% progressive lung disease – may be fatal
                                                             47




  H. capsulatum - Dimorphism
• Filamentous mould in environment
   – Thin septate hyphae, microconidia, and
                              (8-14
     tuberculate macroconidia (8 14 µm)
• Budding yeast (2-4 µm) in tissue
   – Dimorphic transition is thermally dependent
     and reversible (25°C ↔ 37°C).




 Hyphae, micro- and macroconidia   Yeast within histiocyte
                                                             48




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  Opportunistic fungal infections
Fungus                  Disease                  Distribution/
                                                 habitat
Candida spp             candidiasis              Human normal flora


Aspergillus spp         aspergillosis            Ubiquitous; soils.
                                                 grains

Cryptococcus            Cryptococcal             birds
neoformans              pneumonia &
                        meningitis
Rhizopus, Mucor         zygomycosis              Soil, plants


Penicillium marneffii   penicilliosis            SE Asia (China,
                                                 Thailand, India);    49
                                                 bamboo rat




                        Candidiasis
• Genus Candida - diverse group of yeasts
   – Budding yeast, stain Gram-positive
   – ID based on biochemical tests and morphology (corn
     meal agar)
• C. albicans - most important pathogen
   – Multiple forms: budding yeast, true hyphae. Forms
     germ tubes (pseudohyphae) in presence of serum.




   • Other Candida spp: C. tropicalis, C. parapsilosis C. lusitaniae, C.
     krusei, C. glabrata, C. guilliermondii, and C. dubliniensis

                                                                      50




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                             Candidiasis
•       commonest species is Candida albicans.
    –      Commensal of human mucosal surfaces – mouth, vagina, intestinal tract.
    –                                  body s
           Can become pathogenic if body’s defence mechanisms are impaired or
           balance of microbial flora upset.
    –      Infections can affect skin & mucous membranes (mucocutaneous = thrush) or
           be systemic.
•       Oral thrush – neonates, corticosteroid puffers, prolonged treatment with
        antibiotics;
•       Skin folds of obese people, nappy rash in infants
•       Vaginal thrush – diabetes, pregnancy, hormonal imbalance, prolonged
        antibiotic treatment.
    –      Destruction of lactobacilli (normal vaginal flora) allows pH to rise and Candida
                   invade.
           spp can invade
•       Systemic candida infection – candidaemia
    –      generally in association with severe underlying disease (leukaemia,
           other cancers; organ transplantation.
    –      neutropaenia makes people more susceptible


                                                                                          51




                             Candidiasis




         http://www.edison.edu/course_material/                                           52
                                                                                     Figure 21.17




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          Candida infections




                                                 53




            Aspergillus spp.
• More than 100 species of Aspergillus. Septate
                        45 angle.
  hyphae branching at 45° angle
• Omnipresent in environment. A. fumigatus is
  thermotolerant (up to 55oC) and is found in high
  concentrations in compost sites.
• Most human disease caused by A. fumigatus, A.
  flavus, and A. niger.
• Opportunistic pathogen, airborne spread



                                                 54




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                    Aspergillosis
• Almost any organ or system in the human
  b d may b i
  body                l d
             be involved
• Spores inhaled → lung infection in
  susceptible patient → spread to other
  parts of the body via the bloodstream →
  potentially fatal abscesses in various
  organs
• Major problem in bone marrow recipients

                                                          55




                 Cryptococcosis
• Cryptococcus neoformans var neoformans –
  encapsulated yeast found in pigeon droppings & other
  birds;    t    t f th
  bi d most parts of the worldld
• Enters body via respiratory tract → mild asymptomatic
  pneumonitis in most people
• In immunosuppressed people → severe pneumonia
   – Can spread to brain causing meningitis
   – Occurs in about 80% AIDS patients
• Cryptococcal infections more frequently seen in patients
       i i   t id       immunosuppressive th
  receiving steroids or i              i therapy
• Note also Cryptococcus neoformans var gattii –
  associated with flowering Red River gums; infections in
  Indigenous Australians – associated with living in dry
  river beds
                                                          56




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                  Cryptococcus neoformans in CSF




                                                   57




              Zygomycosis
• Infections caused by Mucoraceae
  – Mucor, Rhizopus, Absidia
  – Broad nonseptate hyphae, sporangia
    (rhizoids in some species).
     • Widespread in environment; found in
       decaying vegetables and fruits, soil, old
       bread; grow and sporulate on materials
       containing carbohydrates. Rhizopus
                                       isolate.
       oryzae is most common clinical isolate
  – Invasive infections assoc with
    diabetes, leukopenia and patients
    treated with steroids or deferoxamine
  – Predilection for blood vessel invasion,        58
    thrombosis, infarction




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            Penicillium marneffei
• Only dimorphic species in genus Penicillium
  – Distribution limited to SE Asia, isolated from
    healthy bamboo rats and surrounding soil
      • Infection probably occurs through inhalation
  – Major cause of opportunistic infections in HIV pts
    in SE-Asia - Chronic illness, low-grade fever,
    weight loss, skin lesions, disseminated infection
  – Intracellular forms resemble H. capsulatum;
    extracellular forms exhibit septa (cells divide by
    fission, not budding)
  – Grows as mold at 25-30ºC
      • Produces soluble red pigment
      • Converts to yeast phase at 37ºC                  59




            Penicillium marneffei
• http://www.pmarneffei.hku.hk/




                                                         60




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     Non-infectious fungal diseases
  • Allergies - associated with spores of
         ld
    moulds
  • Fungal toxins
        – Ergotism – Claviceps purpurea
        – Aflatoxins etc (see table)
                • Human disease associated with contaminated food
                  – often grains and cereals
        – Poisonous mushrooms

                                                                                               61




        Mycotoxins and Their Biological Effects
          Mycotoxin                      Biological Effect                   Organism
Aflatoxins                        Hepatocarcinogen                 A. parasiticus, A. flavus
Trichothecenes (T-2,              Dermal toxicity; impairment of   Fusarium, Acremonium,
nivalenol, deoxynivalenol,        immune system; inhibit           Stachyobotris, Trichoderma,
satratoxins, DAS*)
            ,     )               p
                                  protein synthesis, teratogen*
                                           y        ,      g       Trichothecium,,
                                                                   Verticimonosporium
Anthraquinones (luteoskyrin,    Hepatotoxic,                Penicillium, Aspergillus
rugulosin, iridoskyrin, emodin) hepatocarcinogen or mutagen
Citreoviridin                     Neurotoxin; inhibits             Penicillium
                                  mitochondrial ATPase activity,
                                  reduces glycogen synthetase
                                  activity
Naphtoquinones                    Hepatotoxic                      Trychophyton, Penicillium
(xanthomeganin, viomellein)                                        viridicatum
Ochratoxins                       Inhibit phe-tRNA synthase        Aspergillus, Penicillium
Zearalenone (F-2)                 Estrogenic, teratogenic          Fusarium graminearum
Chloropeptide (islandi-toxin)     Hepatotoxin, decreases           Penicillium islandicum
                                  hepatic glycogen synthase
                                  activity
                                                                                               62
     *DAS = diacetoxy-12, 13-epoxytrichotece-9-ene           http://medocs.ucdavis.edu/




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  Treatment of fungal infections
• Australian Guidelines for the use of
     tif    ld      i th treatment of
  antifungal drugs in the t t       t f
  invasive fungal infections (July 2003)
• http://www.racp.edu.au/asid/antifungal/ind
  ex.htm




                                                     63




Antifungal activity of disinfectants &
  antiseptics – time to give 99.99% kill
Agent           A niger   T             C albicans
                          mentagrophyte
                          s
Phenolic (0.36% < 2       <2            <2

Chlorhexidine   <2        <2            <2
(0.02%)
Iodine (1%)     <2        <2            <2

hypochlorite    10        <2            5

cetrimide       <2        20            <2

chlorhexidine   20        > 20          <2

                                                     64




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 Sites of action of antifungal drugs




                                                                    65




      History of antifungal drugs

                      1960s                 1970s
   1950s          Amphotericin B                             1980s
                                          Econazole
Griseofulvin       Miconazole                             Ketoconazole
                                        Miconazole (IV)
 First azole       Clotrimazole                               (po)
                   Flucytosine

     1990s
  Fluconazole                                        Micafungin
 Itraconazole               2000s                   Anidulafungin
 Terbinafine             Caspofungin                Posaconazole
 Lipid Ampho             Voriconazole               Ravuconazole
 formulations                                        Sordarins...

                http://www.doctorfungus.org/l                       66




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                               Antifungals
•   Griseofulvin
     – Inhibits mitosis. Activity limited to dermatophytes.
•   Polyenes (Amphotericin B, nystatin)
     – Bind to ergosterol, disrupt membrane integrity (lower affinity for
        cholesterol). Active against most fungi; significant toxicity.
•   Azoles (fluconazole, itraconazole)
     – Inhibit P450-dependent demethylase required for synthesis of
        ergosterol. Active against many fungi.
•   5-Fluorocytosine
     – Converts to 5-FU, inhibits RNA/DNA synthesis. Resistance develops
        readily. Used in combinations.
•   Allylamines (terbinafine)
     – Inhibits squalene epoxidase (sterol synthesis). Treatment of nail
                                 p y
        infections and dermatophytes.
•   Echinocandins (caspofungin)
     – Inhibit synthesis of glucans in cell wall. Active against major opportunist
        infections eg Aspergillus and Candida.
•   Nikkomycin
     – Chitin synthetase inhibitor – treatment of Blastomyces and Histoplasma
•   Sordarins - specifically inhibit protein synthesis elongation cycle in yeasts
    but do not affect protein synthesis machinery in mammalian systems            67




                   Antifungal Agents
                     Spectrum of Activity
                         http://www.lumen.luc.edu/lumen/MedEd/USMLE/104




                                                                                 68




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