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MEDICALLY IMPORTANT FUNGI DR. BREIDA BOYLE. INTRODUCTION Fungi are a diverse group of sacrophytic and parasitic eukaryotic organisms Kingdom: Mycota Of.

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Presentation on theme: "MEDICALLY IMPORTANT FUNGI DR. BREIDA BOYLE. INTRODUCTION Fungi are a diverse group of sacrophytic and parasitic eukaryotic organisms Kingdom: Mycota Of."— Presentation transcript:


2 INTRODUCTION Fungi are a diverse group of sacrophytic and parasitic eukaryotic organisms Kingdom: Mycota Of 100,000 fungal species only 100 have pathogenic potential for humans, only a few account for clinically important infections Mycoses : Human Fungal Diseases Fungal spores may be important as human allergenic agents

3 INTRODUCTION MYCOSES CUTANEOUS: limited to the dermis SUBCUTANEOUS : when infection penetrates significantly beneath the skin SYSTEMIC : when the infection is deep within the body or disseminated to internal organs


5 TRUE PATHOGENS Epidermophyton species Microsporum species Trichophyton species Actinomadura madurae Cladosporium Madurella grisea Phialophora Sporothrix schenckii Blastomyces dermatitidis Coccidioides immitis Histoplasma capsulatum Paracoccidioides brasiliensis Cutaneous infective agentsSubcutaneous infective agents Systemic infective agents

6 OPPORTUNISTIC PATHOGENS Absidia corymbifera Aspergillus fumigatus Candida albicans Crytococcus neoformans Pneumocystis carinii Rhizomucor pusillus Rhizopus oryzae (R.arrhizus)

7 CLASSIFICATION OF FUNGI Depends on : Characteristic Structures Habitats Modes of Growth Modes of Reproduction

8 Cell Wall and Membrane Composed mainly of chitin rather than peptidoglycan (bacteria)-so unaffected by antibiotics Chitin: consists of a polymer of N- acetylglucosamine Fungal Membrane contains ergosterol rather than cholesterol found in mammalian cells, use in antifungal agents such as amphotericin which binds to ergosterol  pores that disrupts membrane function  cell death

9 Cell Membrane The imidazole antifungal drugs ( clotrimazole, ketoconazole, miconazole) and the triazole antifungal agents (fluconazole, itraconazole) interact with the C-14 α-demethylase to block demethylation of lansterol to ergosterol, vital component of cell membrane and disruption of it`s synthesis results in death

10 HABITAT All fungi are heterotrophs ( their require some form of organic carbon for growth) They depend on transport of soluble nutrients across their cell membrane To do this they secrete degradative enzymes ( proteases etc) into their immediate environment, therefore they live on dead organic material So Natural Habitat : is soil or water containing decaying organic matter

11 MODES OF FUNGAL GROWTH FILAMENTOUS MOLDS UNICELLULAR YEASTS However there are some dimorphic fungi ( they switch between these Two forms depending on their environment)

12 Filamentous (mold-like) Fungi Thallus (vegetitive body) –mass of threads with many branches resembling cotton ball Mass: mycelium Threads: hyphae, tubular cells that in some fungi are divided into segments –septate whereas in other fungi the hyphae are uninterrupted by crosswalls-nonseptate Grow by branching and tip elongation

13 YEAST like FUNGI These fungi exist as populations of single, unconnected, spheroid cells, not unlike many bacteria, although they are sometimes 10 times larger than a typical bacterial cell Yeasts reproduce by budding Some fungal species particularly those that cause systemic infection exist as dimorphic fungi


15 SPORULATION The principle way in which fungi reproduce and spread within the environment Fungal spores are metabolically dormant, protected cells, released by the mycelium in enormous numbers Borne by the air or water to new sites, where they germinate and establish new colonies Spores can be generate sexually or asexually

16 ASEXUAL SPORULATION Colour of a particular fungus seen on bread, culture plate is due to the Conidia, easly airborne and disseminated (MITOSIS)

17 SEXUAL SPORULATION meiosis Relatively rare compared to asexual sporulation, and spore shape often Used as a method of identification

18 CUTANEOUS MYCOSES -DERMATOPHYTOSES EPIDEMIOLOGY Three genera-Trichophyton, Epidermophyton, Microsporum Anthropophilic-reside on the human skin Zoophilic-reside on the skin of domestic and farm animals Geophilic-reside in the soil Transmission from humans or animals is by infected skin scales

19 PATHOLOGY Dermatophytes use keratin as a source of nutrition Therefore they infect skin, hair, nails All 3 organisms infect attack skin, Microsporum does not infect nails and Epidermophyton does not infect hair, they not invade underlying non-keratinized tissues

20 CLINICAL SIGNIFICANCE DERMATOPHYTOSES Characterized by itching,scaling skin patches that can become inflamed and weeping Infection in different sites may be due to different organisms but is given one name

21 Tinea pedis(Athlete`s foot) Common organisms are Trichophyton rubrum, Trichophyton mentagrophytes and Epidermophyton floccosum. Initially between the toes spreads to nails, yellow and brittle Secondary bacterial infection Id Reaction

22 Tinea corporis( Ringworm) Epidermophyton floccosum, Trichophyton, Microsporum Advancing annular rings with scaly center Periphery of ring area of active fungal growth, usually inflammed and vesiculated Non-Hairy areas of trunks mostly

23 Tinea capitis( scalp ringworm) Trichophyton and Microsporum Depends on area Small scaling patches to involvement of entire hair with hairloss Microsporum infects hair shafts, Wood`s lamp

24 TINEA CRURIS/UNGUIUM Epidermophyton, Trichophyton rubrum, simliar to ringworm but thighs and genitalia Trichophyton rubrum, nails thickened discoloured and brittle Treatment for months until all of the infected nail grows out and is trimmed off

25 Treatment Samples to be sent for fungal staining and culture Infected skin may be treated with topical application of antifungal agents miconazole and clotrimazole Refractory lesions oral griseofulvin and itraconazole, terbinafine Infections of hair and nails usually require systemic ( oral) therapy

26 SUBCUTANEOUS MYCOSES( dermis, subc tissues and Bone) Causative organisms reside in the soil and in decaying or live vegetation Almost always acquired through traumatic lacerations or puncture wounds Common among those who work with soil and vegetation and have little protective clothing Not usually transmitted humans to humans Usually confined to tropics and subtropics with exception of Sporotrichosis in USA

27 Sporotrichosis Sporothrix schenckii-dimorphic fungus Granauloma ulcer at a puncture skin usually a thorn prick and may produce secondary lesions along draining lymphatics In most disease is self-limiting may exist in chronic form Treatment oral itraconazole Chromomycosis : Phialophora or Cladosporium

28 Mycetoma Madurella grisea, Actinomadura madura Localized abscess usually on the feet, that discharge pus serum and blood Has coloured grains( compact hyphae) black, white, red or yellow depending on organism

29 Diagram of Systemis mycoses(dimorphic, yeast in infective tissue) Eastern US Males

30 Clinical significance Simliar to Tb in that asymtomatic primary infection is seen whereas chronic pulmonary or disseminated infection rare In the immunocompetent usually mild and self limiting In the immunocompromised the same infections can be life threatening

31 Coccidiodomycosis Coccidioides immitis Most in arid areas of south-western US In the soil forms arthrospores Spores airborne, germinate in the lungs and produce sphercules filled with many endospores- new spherule In disseminated cases lesions in the bone or CNS -meningitis

32 Histoplasmosis Histoplasma capsulatum In the soil conidia, germinate lungs into yeast-like cells Becomes engulfed by macrophages and XX Benign self-limiting or chronic, progressive, fatal Disseminated disease only fungus intracellular RES parasitism Area Ohio and Mississippi River area DX: Culture or Exoantigen (immunodiffusion assay) AIDS patients at particular risk Treatment : Amphotericin or Itraconazole

33 OPPORTUNISTIC PATHOGENS Absidia corymbifera Aspergillus fumigatus Candida albicans Crytococcus neoformans Pneumocystis carinii Rhizomucor pusillus Rhizopus oryzae (R.arrhizus)

34 OPPORTUNISTIC MYCOSES Those that affect the immunocompromised but are rare in normal individual Organ transplantation, post chemotherapy for cancer, immunodeficient due to Aids and congenital immunodeficiency states Candida species most commonly occurring fungal pathogen in the ICU setting

35 CANDIDIASIS(candidiosis) Candida albicans and other candida species which are normal flora in the mouth, skin, vagina and intestines C.albicans is dimorphic May occur as a results of overgrowth as suppression of bacteria by antibiotics Manifestations depend on the site e.g. oral candidiasis and vaginal candidiasis and disseminated candidiasis in cancer patients, post GI surgery and AB`s, systemic corticosteroids

36 CRYTOCOCCOSIS Crytococcus neoformans, found worldwide Especially found in soil containing bird(esp. pigeons) droppings Characteristic thick capsule that surrounds budding yeast cell –seen Indian Ink Most common form is mild subclinical lung infection In the immunocompromised often disseminates to the brain, meningitis often fatal However half those with crytococcal meningitis have no obvious immune deficiency

37 ASPERGILLOSIS Several species of genus Aspergillus, mostly Aspergillus fumigatus Worldwide distribution, ubiquitous Filamentous molds, produce large numbers of conidiospores Reside in soil, decomposing organic matter and dust, associated outbreks with construction work Disease presentation depends on immunologic status of patient

38 ASPERGILLOSIS Acute Aspergillus infections Most severe and often fatal form of aspergillosis is acute invasive infection of the lung  dissemination to brain etc Less severe form gives rise to a fungus ball( aspergilloma), a mass of hyphal tissue that forms in lung cavities derived from prior disease

39 Allergic Aspergillosis Relatively rare, can arise from inhalation of spores, without sussequent extensive spore germination hyphal invasion The allergic reaction results in bronchial constriction Diagnosis by immunoelectrophoresis

40 MUCORMYCOSIS Most often caused by Rhizopus oryzae and less often by other members of the Mucorales such as Absidia corymbifera, Rhizopus pus Ubiquitous in nature, spores found in great abdunance on rotting fruit and old bread Usually restricted to those with underlying conditions such as burns, leukaemia or diabetus mellitus The most common form of the disease can be fatal within a week-Rhino cerebral Mucormycosis

41 PNEUMOCYSTIS CARINII PNEUMONIA Caused by a unicellular eukaryote, Pneumocystis carinii Before the use of immunosuppressive agents and the onset of the AIDS epidemic, PCP was a rare disease It is one of the most common opportunisitic diseasesof individuals treated with HIV-1 and usually fatal if untreated It does not contain ergosterol and has not been cultured

42 PCP Various cellular forms encysted group of dormant cells and vegetitive form –trophozoite Ubiquitous Activation of preexisting dormant cells in the lungs in immunodeficient persons The encysted forms induce an inflammination of the alveoli-exudate which blocks gas exchange Diagnosis by microscopic examination, by silver stain or fluorescence of bronchial washings or biopsy

43 LABORATORY IDENTIFICATION Standard media –Sabouraud`s agar, potato dextrose agar, low ph 5.0, inhibits bacterial growth but allows fungal colonies to form Cultures can be started from spores or hyphae fragments Specimens: blood, pus, CSF, sputum, tissue biopsies, skin scrapings, nail clippings Identification by the morphology of conidia structures and carbonhydrate assimiliation tests

44 LABORATORY DIAGNOSIS OF FUNGAL INFECTION Specimens Depends on site of infection Systemic: -Blood culture( really only useful for yeast-low sensitivity) or - antigen testing e.g.crytococcal and histoplamsosis antigen Pneumonia: Bronchoscopy washings or brushings for staining and fungal culture or bronchial biopsy

45 LABORATORY DIAGNOSIS OF FUNGAL INFECTIONS Meningitis: Cerebrospinal fluid for methylene blue staining and indian ink and crytococcal antigen and fungal culture If Skin infection require skin scrapings If nail infection require nail clippings Galactomannan antigen testing for aspergillus infection

46 LABORATORY DIAGNOSIS FUNGAL INFECTIONS Types of tests carried out Fungal Staining – methylene blue staining or wet prep using KOH to dissolve tissue material Fungal culture on media that encourages fungal growth e.g. PDA Antigen Testing i.e. to test for antigen present in the wall of fungus e.g crytococcal antigen, galactomannan used in serum and CSF samples PCR not used on a routine basis on samples

47 MANAGEMENT OF FUNGAL INFECTIONS Some such as superfical skin infections require topical therapy only with cream e.g.nystatin cream Some require local therpy e.g. pessaries for vaginal candidasis Some require oral therapy for skin and nail infections up to 1 year e.g. terbinafine In the immunocompromised systemic therapy required e.g., voriconazole,fluconazole i./v or amphotericin

48 MANAGEMENT OF FUNGAL INFECTIONS Important to diagnose fungal infections early in the immunocompromised as there is a high mortality associated with infection Empirical therapy often started in advance of laboratory diagnosis in these patients








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