General properties of fungi

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General properties of fungi

  1. 1. General properties of fungi Dr. Pendru Raghunath Reddy Assistant Professor of Microbiology Dr. VRK Women’s Medical College
  2. 2. Introduction • Mykes (Greek word) : Mushroom • Fungi are eukaryotic protista; differ from bacteria and other prokaryotes. 1. Cell walls containing chitin (rigidity & support), mannan & other polysaccharides 2. Cytoplasmic membrane contains ergosterols 3. Possess true nuclei with nuclear membrane & paired chromosomes 4. Cytoplasmic contents include mitochondria and endoplasmic reticulum 5. Divide asexually, sexually or by both 6. Unicellular or multicellular 7. Most fungi are obligate or facultative aerobes
  3. 3. • Cell wall consists of chitin not peptidoglycan like bacteria • Thus fungi are insensitive to antibiotics as penicillins • Chitin is a polysaccharide composed of long chain of n- acetylglucosamine. • Also the fungal cell wall contain other polysaccharide, β- glucan, which is the site of action of some antifungal drugs. • Cell membrane consist of ergosterol rather than cholesterol like bacterial cell membrane • Ergosterol is the site of action of antifungal drugs, amphtericin B & azole group
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  5. 5.  Diverse group of heterotrophs. – Many are ecologically important saprophytes (consume dead and decaying matter) – Others are parasites.  Most are multicellular, but yeasts are unicellular.  Most are aerobes or facultative anaerobes.  Cell walls are made up of chitin (polysaccharide).  Over 100,000 fungal species identified. Only about 100 are human or animal pathogens. – Most human fungal infections are nosocomial and/or occur in immunocompromised individuals (opportunistic infections). 
  6. 6. In addition to those species which are generally recognized as pathogenic to man it is firmly established that under unusual circumstances of abnormal susceptibility of patient, or the traumatic implantation of the fungus, other fungi are capable of causing lesions. Those are called (Opportunistic fungi)
  7. 7. Predisposing factors • Use of Antibiotics, • Use of steroids, • A debilitating condition of the host, as Diabetes. • A concurrent disease such as leukaemia • Immunosuppressive conditions 8
  8. 8. Fungal Morphology Molds Yeasts Many pathogenic fungi are dimorphic, forming hyphae at ambient temperatures but yeasts at body temperature. 7/21/2013 Dr.T.V.Rao MD 9
  9. 9. Understanding the Structure of Fungus • Simplest fungus :- Unicellular budding yeast • Hypha :- Elongation of apical cell produces a tubular, thread like structure called hypha • Mycelium :- Tangled mass of hyphae is called mycelium. Fungi producing mycelia are called molds or filamentous fungi. • Hyphae may be septate or non-septate (coenocytic hyphae)
  10. 10. Mycelium • Mass of branching intertwined hyphae – Vegetative – Aerial
  11. 11. Vegetative types • Favic chandeliers • Nodular organs • Racquet hyphae • Spiral hyphae
  12. 12. Classification of fungi 1.Morphological classification 2.Systematic classification
  13. 13. 1. Yeasts 2. Yeast-like fungi 3. Filamentous fungi (molds) 4. Dimorphic fungi Morphological classification
  14. 14. Yeasts 1. These occur in the form of round or oval bodies which reproduce by the formation of buds known as blastospores 2. Yeasts colonies resemble bacterial colonies in appearance and in consistency 3. The only pathogenic yeast in medical mycology is Cryptococcus neoformans
  15. 15. Yeast colonies Mucoid colonies
  16. 16. Cryptococcus neoformans Downloded from www.pharmacy123.blogfa.com
  17. 17. Yeast-Like 1.These are fungi which occur in the form of budding yeast-like cells and as chains of elongated unbranched filamentous cells which present the appearance of broad septate hyphae. these hyphae intertwine to form a pseudomycelium. 2. The yeast like fungi are grouped together in the genus Candida.
  18. 18. Candida Colonies
  19. 19. Candida albicans SEM
  20. 20. Filamentous Fungi The basic morphological elements of filamentous fungi are long branching filaments or hyphae, which intertwine to produce a mass of filaments or mycelium Colonies are strongly adherent to the medium and unlike most bacterial colonies cannot be emulsified in water The surface of these colonies may be velvety, powdery, or may show a cottony aerial mycelium.
  21. 21. mycelium: septate mycelium: non septate
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  23. 23. Colony Morphology
  24. 24. Dimorphic Fungi These are fungi which exhibit a yeast form in the host tissue and in vitro at 370C on enriched media and mycelial form in vitro at 250C Examples: Histoplasma capsulatum Blastomyces dermatitidis Coccidioides immitis Paracoccidoides brasiliesis Penicillium marneffei Sporothrix schenckii
  25. 25. Histoplasma capsulatum - Dimorphism • Filamentous mold in environment – Thin septate hyphae, microconidia, and 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
  26. 26. Systematic classification • Based on sexual spores formation: 4 classes 1. Zygomycetes 2. Ascomycetes reproduce sexually 3. Basidiomycetes 4. Deuteromycetes (fungi imperfectii)
  27. 27. Zygomycetes • Lower fungi • Broad, nonseptate hyphae • Asexual spores - Sporangiospores: present within a swollen sac- like structure called Sporangium • Examples: Rhizopus, Absidia, Mucor
  28. 28. Ascomycetes • Sexual spores called ascospores are present within a sac like structure called Ascus. • Each ascus has 4 to 8 ascospores • Includes both yeasts and filamentous fungi
  29. 29. Ascomycetes • Narrow, septate hyphae • Asexual spores are called conidia borne on conidiophore • Examples: Penicillium, Aspergillus
  30. 30. Basidiomycetes Sexual fusion results in the formation of a club shaped organ called base or basidium which bearspores called basidiospores Examples: Cryptococcus neoformans, mushrooms
  31. 31. Deuteromycetes or Fungi imperfectii • Group of fungi whose sexual phases are not identified • Grow as molds as well as yeasts • Most fungi of medical importance belong to this class • Examples: Coccidioides immitis, Paracoccidioides brasiliensis, Candida albicans
  32. 32. Reproduction and sporulation Types of fungal spores 1.Sexual spores 2.Asexual spores
  33. 33. Sexual spores • Sexual spore is formed by fusion of cells and meiosis as in all forms of higher life • Ascospores – Ascus – Ascocarp • Basidiospores • Zygospores
  34. 34. Asexual spores  These spores are produced by mitosis 1. Vegetative spores 2. Aerial spores
  35. 35. Vegetative spores • Blastospores: These are formed by budding from parent cell, as in yeasts • Arthrospores – formed by segmentation & condensation of hyphae • Chlamydospores – thick walled resting spores e.g. C.albicans
  36. 36. Aerial spores 1. Conidiospores Spores borne externally on sides or tips of hyphae are called conidiospores or simply conidia 2. Microconidia 3. Macroconidia 4. Sporangiospores
  37. 37. • Microconidia - Small, single celled • Macroconidia – Large and septate and are often multicellular
  38. 38. Immunity to fungal diseases  The defense to fungal infection involves both innate and aquired immunity  The passive protection is provided by intact skin and mucosal surfaces  The fatty acids like sebum also provide protection because of their antifungal activity  The alveolar macrophages are important in engulfing cells in lungs which are removed by ciliary action and coughing  A variety of innate defense factors in saliva such as lysozymes and lactoferrin contribute to mucosal protection
  39. 39. Cellular immunity  For the most of fungi, cellular immunity is mainstay of host defenses  Monocyte-macrophage activity, especially in respiratory tract, appears to be major defence mechanism against most fungi  Renal transplant recipients have peculiar predilection for cryptococcal infection Humoral immunity  The precise role of humoral immunity in host defense against fungal infections is difficult to determine
  40. 40. Diagnosis of fungal diseases 1. Clinical diagnosis 2. Laboratory diagnosis
  41. 41. Clinical diagnosis  The clinical criteria may give presumptive diagnosis of fungal infections  The superficial and subcutaneous mycoses often produce characteristic lesions that strongly suggest their fungal etiology  In case of systemic mycoses, there is no sign or symptom that specifically suggests a fungal disease
  42. 42. Laboratory diagnosis Specimens collection 1. Respiratory specimens 2. CSF 3. Blood 4. Tissue, Bone marrow and body fluids 5. Skin, hair and nail 6. Urine, stool 7. Vaginal secretions 8. Corneal scrapings
  43. 43. Direct examination  The direct demonstration of fungal elements is essential in establishing diagnosis by detecting presence of causative agent in the clinical material  The following procedures are adopted to directly observe fungi in clinical specimens 1. Wet mounts 2. Histopathology 3. Fluorescent-antibody technique 4. Gram staining
  44. 44. Wet mounts KOH wet mount Slide KOH  Most of the specimens can be examined in wet mounts after partial digestion with 10-20% KOH  The clinical specimens like skin, hair and nails should be mounted under cover slip in KOH on slide  This clears material within 5 – 20 minutes, depending on its thickness  A slight warming over a low flame hastens digestion of keratin
  45. 45.  KOH can also be supplemented with DMSO to increase clearing of fungi especially in skin scrapings and nail clippings  The KOH can be supplemented with a fluorescent dye, calcofluor white (CFW)  The CFW supplemented KOH especially in corneal scrapings can detect even scanty amount of fungal elements Tube KOH  The tube KOH is prepared mainly for biopsy specimens, which take longer time for dissolution  The homogenized biopsy tissue is dissolved in 10% KOH and examined after keeping for an overnight in an incubator at 370C
  46. 46. KOH mount Blastomyces dermatitidisMold (note: septate hyphae)
  47. 47. KOH mount Ectothrix Endothrix
  48. 48. Other methods The wet india ink and nigrosin preparations are also very useful in making diagnosis of certain capsulated fungi Histopathology The histopathological examination of biopsy specimens is an excellent way to diagnose mycotic infections The H&E stain is routine procedure in histopathology laboratory and stains most of fungi
  49. 49. H&E stain Endospores and sporangia of Rhinosporidium seeberi Cryptococcus neoformans
  50. 50. Blastomyces dermatitidis Rhizopus species H&E stain
  51. 51. The specific fungal stains, such as periodic acid-Schiff (PAS), Grocott-Gomori’s Methenamine silver (GMS) and Gridely stains are widely used for demonstrating fungi in tissues Mayer’s mucicarmine stain can also be used specifically to show capsular material of Cryptococcus, endospores and sporangia of Rhinosporidium seeberi
  52. 52. PAS stain GMS stain
  53. 53. Fluorescent-antibody staining May used to detect fungal antigen in clinical material such as pus, blood,CSF, tissue impression smears and in paraffin sections of formalin fixed tissue It is less satisfacory for sputum specimens Detects fungus when there are only few organisms present, as seen in pus from sporotrichosis Its use is limited by restricted availability of specific antisera
  54. 54. Gram staining All fungi are gram positive Gram stained smear of Candida species
  55. 55. Fungal culture The solid media are employed for fungal culture The medium commonly employed is emmon’s modification of Sabouraud Dextrose Agar (SDA) [pH – 5.4] The media may supplemented with antibiotics, such as gentamicin and chloramphenicol to minimize bacterial contamination and cycloheximide to inhibit saprophytic fungi The special media may be used for isolation and to help rapid identification, when identity of a particular pathogen is strongly suspected Eg: Bird seed agar for Cryptococcus neoformans Potato dextrose agar, Brain heart infusion (BHI) agar and Czapek Dox agar may also be used for isolation of fungi
  56. 56. Incubation Cultures are routinely incubated in parallel at room temperature (for weeks) and at 370C for days Many fungi develop relatively slowly and cultures should be retained for atleast 2-3 weeks (in some cases upto 6 weeks) before being discarded Yeasts usually grow within 1-5 days
  57. 57. Interpretation of fungal cultures  The significance of fungal isolate depends on its source and identity  The isolation of an established pathogen such as H. capsulatum or Coccidioides species from any specimen is generally regarded as an evidence of infection  In case of commensal or opportunistic fungi following points should be considered 1. Isolation of same strain in all culture tubes 2. Repeated isolation of same strain in multiple specimens 3. Immune status of patients and 4. Serological evidence to confirm significance of isolate
  58. 58. Identification of fungi Gross or macroscopic examination of cultures Microscopic examination 1. Tease mount 2. Slide culture
  59. 59. Tease mount For microscopic examination, fragment of fungal culture is teased out using two teasing needles and placed on a glass slide in drop of LCB stain To study the morphology of hyphae, spores and other structures, tease mounts are prepared in lactophenol cotton blue (LCB) which contains lactic acid, phenol, glycerol and cotton blue Microscopic characteristics that should be observed are the following 1. Sepatate versus sparsely septate hyphae 2. Spores or conidia
  60. 60. Slide culture Is used to study undisturbed morphological details of fungi, particularly relationship between reproductive structures like conidia, conidiophore and hyphae It is indicated when teased mount of LCB is inconclusive in particular fungal isolate
  61. 61. Procedure Place sterile microscopic slide on bent glass rod at the bottom of petri dish A piece of one square centimeter block of cornmeal agar or potato dextrose agar is put up on the slide Inoculate the fungal strain under identification at four sides of agar block Cover the inoculated block with sterile coverslip and incubate at 250C in BOD incubator
  62. 62. Slide culture
  63. 63. Add a little sterile distilled water on filter paper to avoid drying of agar When growth appears, place drop of LCB on slide and coverslip from block Cellophane tape preparation A piece of tape is gently laid over portion of fungal colony and slowly lifted and place over a glass slide containing LCB solution This preparation has come into greater use to overcome obstacles of time consumption and requirement of extra equipment to prepare slide culture
  64. 64. Aspergillus Penicillium
  65. 65. Miscellaneous tests for the identification of molds 1. Hair perforation test 2. Urease test 3. Thiamine requirement Miscellaneous tests for identification of yeasts Germ tube production, carbohydrate assimilation, chromogenic substrates, potassium nitrate assimilation, temperature studies and urease
  66. 66. Serologic tests Detection of antibodies 1. Immunodiffusion 2. Countercurrent immunoelectrophoresis (CIE) 3. Whole cell agglutination 4. Complement fixation 5. ELISA Detection of antigens 1. Latex particle agglutination 2. ELISA
  67. 67. Molecular techniques 1. PCR 2. DNA probes
  68. 68. Mycoses Infection caused by fungus is known as mycosis (Plural mycoses) Classification of mycoses Classification of fungal disease according to primary sites of infections 1. Superficial mycoses 2. Cutaneous mycoses 3. Subcutaneous mycoses 4. Systemic mycoses 5. Opportunistic mycoses

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