Presentation on theme: "Characteristics of Fungi"— Presentation transcript:
1 Characteristics of Fungi Non-motile eukaryotes lacking chlorophyllContain nucleus, mitochondria, 80S ribosomesCell wall is composed of polysaccharides , polypeptides and chitin and the cell membrane contains sterol which prevent many antibacterial antibiotics being effective against fungi.Larger than bacteriaRelatively simple nutritional requirements, wide range of growth ratesForm visible colonies in days to weeksUnicellular or multicellular depending on the speciesFungi can be divided into: Yeast, Mould (filamentous fungi) and Dimporphic fungi
2 Molds Multicellular, tubular structures (hyphae) Hyphae can be septate (regular crosswalls) or nonseptate (coenocytic) depending on the species (grow by apical extension)Vegetative hyphae grow on or in media (absorb nutrients); form seen in tissue, few distinguishing featuresAerial hyphae contain structures for production of spores (asexual propagules); usually only seen in culture
3 Molds - identification Identification based on colony morphology (pigment, texture) and morphology of reproductive structuresConidia - spores formed by budding (blastoconidia) or disarticulation of existing hypha (arthroconidia)Sporangiospores - produced by free-cell formation within sporangium in nonseptate molds11ConidiopsporesPhialidesVesicleConidiophoreSeptate hyphae3sporangiumsporangiophoreEndosporesNonseptatehyphae5. rhizoids2342545
5 YeastsUnicellular, 3-5 µm, reproduce by budding (blastoconidia formation) or fissionIdentified by microscopic morphology (grow on cornmeal agar) and biochemical tests (sugar assimilation, enzymatic activity).Molds and yeast are not exclusive forms, some species may exist in both yeast and mold forms (dimorphism).
6 Classification of Fungi Taxonomy is based on structural features of the teleomorph (sexual phase).Zygomycota - includes all fungi with nonseptate hyphaeAscomycota - includes most human pathogensBasidiomycota - mainly plant pathogensDeuteromycota (fungi imperfecti)
7 Isolation of fungi Direct examination:- Wet specimen preparations e.g. Aspergillus hyphae in sputum or Cryptococcus neoformans in CSF (mixed with india ink)Potassium hydroxide (KOH) cleared specimens , e.g. dermatophyes (ringworm fungi) in skin scrapings, nails or hairStained preparation: e.g. Candida albicans in Gram stained smears of vaginal discharge or pneumocystis carinii in Giemsa or other stained preparations of broncho-alveolar lavage or sputum.
8 Isolation of fungi Culture Media Incubation General purpose media BHI + blood, inhibitory mold agarSabouraud dextrose agarMycoselSabouraud + chloramphenicol and cycloheximideFor isolation of dermatophytes (some pathogenic fungi are inhibited by cycloheximide)Incubation30°C for 30 days
10 Fungal Infections Type of infection Example Fungi generally have low pathogenic potentialOnly a few true pathogens; many opportunistsMost are acquired from exog/environ sourcesPathology caused by tissue invasion and/or host inflammatory response. Many fungal infections can be characterized by extent of invasionType of infection Examplesuperficial Malasezzia furfurcutaneous dermatophytessubcutaneous sporotrichosisdeep/systemic histoplasmosisopportunistic candidiasis
11 Dermatophytes Fungi that cause superficial/cutaneous infections Confined to keratinized tissue (hair, skin, nails)Cause of ringworm (eg tinea capitis, tinea pedis); inflammation greatest at advancing edge.All are molds. Many species produce macroconidiaEpidermophyton (2 spp), Microsporum (16 spp), Trichophyton (24 spp)Transmitted indirectly via desquamated skin and hair (combs الامشاط hatsقبعه , showers, etc).Diagnosis based on direct examof scrapings,culture on selective media.M. canis
12 Subcutaneous MycosesCaused by direct inoculation of organisms from soil or decaying plantsGenerally cause localized infectionHands and feet are most common sitesSporotrichosis داء الشعيرات المبوغةCaused by dimorphic fungus Sporothrix schenkiiMold in environment, yeast in infected tissueCommonly affects hands trauma from thorns شوكه(eg rose gardens); causes lympho-cutaneous infectionExtracutaneous (pulmonary) and disseminated disease uncommon
13 Subcutaneous Mycoses (continued) Chromoblastomycosis الفطر البرعمي الملونSlow, progressive, granulomatous infection.Skin lesions contain dark brown sclerotic bodies.Caused by dematiaceous (black) molds, eg Cladosporium, Phialophora.MycetomaSwollen lesion, granules (containing organisms) draining from sinuses.Can be caused by fungi eg Pseudoallescheria or actinomycetes (prokaryotes)
14 Candidiasis Genus Candida - diverse group of yeasts Budding yeast, stain Gram-positiveID based on biochemical tests and morphology (corn meal agar)C. albicans - most important pathogenMultiple forms: budding yeast, pseudohyphae, true hyphae. Forms germ tubes (in presence of serum).
15 Pathogenesis of Candida infections Most infections are endogenousCandida is component of normal oral, GI, vaginal floraPathogenic factorsEssential role of mucosal adherenceAlterations in micro-environment and/or microbial flora predispose to symptomatic infection.Germ tube formation, proteinases, phospholipases may contribute to local invasion by C. albicans
17 Candida infections Candidemia/disseminated candidiasis Candida spp are 4th leading cause of nosocomial bloodstream infectionsAntibiotics, iv catheters increase riskAntibiotics eliminate normal GI flora, permit overgrowth of Candida and entry across damaged mucosaIVs provide entry through skinDissemination to kidney, brain, myocardium, eye is common.Ocular candidiasis - white cotton ball-like lesions of retina; can cause blindness
18 Candida infections (continued) Urinary tract candidiasisUsually seen in pts with urinary catheter.Hepatosplenic candidiasisOccurs in severely compromised (neutropenic) pts. Multifocal abscesses
19 Candidiasis - Diagnosis Direct microscopic examinationImportant to demonstrate tissue invasion in mucosal infection; positive culture alone may be due to colonizationCultureCandida spp grow well on standard media.Candidemia readily detected with commercial blood culture systems.
20 Cryptococcus neoformans Encapsulated yeastIdentification based on presence of capsule, urease, growth at 37°C, melanin synthesis, and sugar assimilation.Major virulence factorsPolysaccharide capsuleAntiphagocyticImmunosuppressiveMelanin synthesis
21 C. neoformans - Clinical features Acquired by inhalationMost infections are asymptomatic. May present as isolated pulmonary nodule (r/o carcinoma)Cryptococcal meningitisDissemination from lung. Life-threateningMajor opportunistic infection in HIV pts with low CD4 counts
22 Cryptococcocal meningitis DiagnosisCSF WBC count may not be elevatedPoor prognostic signDirect detection of capsular antigen in CSFLatex agglutination or EIAHigh sensitivity and specificity; has displaced India ink (lacks sensitivity)Culture - gold standardTreatmentAmphotericin B + 5-fluorocytosineIn HIV patients, C. neoformans cannot be eradicated, requires suppressive therapy.
23 Histoplasma capsulatum - Dimorphism Filamentous mold in environmentThin septate hyphae, microconidia, and tuberculate macroconidia (8-14 µm)Budding yeast (2-4 µm) in tissueDimorphic transition is thermally dependent and reversible (25°C 37°C).Hyphae, micro- and macroconidiaYeast within histiocyte
24 H. capsulatum - Epidemiology H. capsulatum can be cultured from soil in endemic areas. Abundant growth in soil containing bird feces (starling roosts, chicken houses) or bat guano (caves).
25 H. capsulatum - Pathogenesis Conidia or hyphal fragments are inhaled, ingested by macrophages.Organisms convert to yeast phase, proliferate in nonimmune macrophages, and spread through RES.Dissemination is common and occurs early, but is usually asymptomatic.CMI response results in macrophage activation, increased fungicidal activity. Infection is contained but not necessarily eradicated.
26 Histoplasmosis - Self-limited Syndromes Acute pulmonary histoplasmosis accounts for most cases of symptomatic infectionFever, chills, headache, myalgia, anorexia, nonproductive cough, pleuritic chest pain.Enlarged lymph nodes, patchy infiltrates.Patients usually improve in several weeks.5-10% symptomatic cases develop inflammatory syndromes (arthritis, erythema nodosum, or pericarditis)
27 Chronic pulmonary histoplasmosis Slowly progressive pulmonary disease.Usually associated with preexisting lung disease.Cough, dyspnea, chest pain, fatigue, fever, night sweats, and weight lossUsually progresses if untreatedAmB or itraconazole (depending on disease severity) reduces symptoms, improves radiographic findings, eliminates H. capsulatum from sputum
28 H. capsulatum - CultureHistoplasma produces mycelial growth with characteristic warty مثل الثألولconidia when cultured at room temperature.Small microconidia and characteristic large , round , spiny macroconidia are produced.At 37 C on certain media it is possible to induce the yeast phase of this dimorphic fungusSputum best for pulmonary histoplasmosisBone marrow or blood best for disseminated histoplasmosis
29 H. capsulatum – Direct examination Examination of infected tissue (eg bone marrow, liver, skin, GI mucosa) can provide rapid presumptive evidence of disseminated histoplasmosisIntracellular yeasts can be seen on peripheral smears in severe disseminated diseaseNEJM 342:28
30 C. immitis - DimorphismGrows as hyphae in environment. Forms thick-walled arthroconidia alternating with thin-walled cells.Spherule كرية filled with endospores in infected tissue.
31 C. immitis - Pathogenesis Arthroconidia are inhaled and convert to spherules that grow to µm. Partially resistant to killing by phagocytic cells.Spherules undergo multiple nuclear divisions and segmentation of cytoplasm to produce hundreds of endospores (2-5 µm). The spherule ruptures, releasing endospores that form new spherules.
32 C. immitis - Epidemiology Can be cultured from soil in areas where disease is endemic. Expected number of infections is 100,000 annually
33 C. immitis - Respiratory Infections 40% of pulmonary infections are symptomaticMost are self-limitedFatigue, cough, chest pain. May also have fever, dyspnea, myalgia, and headachePulmonary nodules4% of infections give rise to solitary وحيدة nodule ( 5 cm)Can form cavities, infreq rupture into pleural space
34 C. immitis - Disseminated infections Occurs in ~ 0.5% of infections. Increased risk:HIV, organ transplants, steroids, Hodgkin’sSkin is most common site of disseminationJoints and BonesProminent synovitis, effusion; knee most commonVertebrae (multiple) > long bonesculture (50%) and histopathology for diagnosisMeningitisHeadache, vomiting, alt mental status. WBC (mono), prot, gluc in CSF. Culture usually neg.
35 C. immitis - Culture and Histopathology Culture - white fluffy وبريmold at 25-30ºC.Arthrospores are suggestive but not diagnosticHistopathologyAcute inflammation (PMNs and Eos) assoc with active infection and ruptured spherulesGranulomas assoc with chronic infection, unruptured spherules
36 Blastomyces dermatitidis MicrobiologyHyphae with microconidia at room tempConvert to broad-based budding yeast at 37ºC.pulmonary infection (asymptomatic or pneumonia); chronic pulmonary disease commonDisseminated disease: skin (common) and bones
37 B. dermatitidis - Diagnosis CultureWhite light tan mold at room temp, not diagnosticIdentification based on conversion to yeast at 37ºC,HistopathologyThick walled broad based budding yeastsuppurative and/or granulomatous inflammation
38 Paracoccidiodes brasiliensis MicrobiologyHyphae at room temp.Converts to yeast with multiple buds at 37ºC.Probably acquired by inhalation. Pulmonary infection can be asymptomatic, acute, or chronicExtrapulmonary disease in adults > 30 usually involves oropharyngeal mucosa and regional lymph nodes.
39 Penicillium marneffei Only dimorphic species in genus PenicilliumInfection probably occurs through inhalationChronic illness, low-grade fever, wt loss, skin lesions, disseminated infectionIntracellular forms resemble H. capsulatum; extracellular forms exhibit septa (cells divide by fission, not budding)Grows as mold at 25-30ºCProduces soluble red pigmentConverts to yeast phase at 37ºC
40 Aspergillus spp.More than 100 species of Aspergillus. Septate hyphae branching at 45° angle.Omnipresent موجودة بكل مكانin environment. A. fumigatus is thermotolerant (up to 55oC) and is found in high concentrations in compost اوراق الشجرsites.Most human disease caused by A. fumigatus, A. flavus, and A. niger.Opportunistic pathogen, airborne spread
41 Aspergillus Infections Allergic bronchopulmonary aspergillosisAspergilloma (fungus ball)Colonization of preexisting lung cavity (TB, abscess, etc(.Invasive pulmonary aspergillosisOccurs in pts with immunosuppression and neutropenia.Vascular invasion, infarction, cavitationHematogenous dissemination common (ocular, cerebral, cutaneous involvement)
42 Aspergillosis - Diagnosis Direct examinationDifficult to distinguish branching septate hyphae of Aspergillus spp from other opportunistic fungi, eg Pseudallescheria, Fusarium.CultureAspergillus spp grow well on standard media. Airborne contaminants are a problem.Need to see several colonies from one specimen or same organism in multiple specimens.
43 Mucormycosis Infections caused by Mucoraceae Mucor, Rhizopus, Absidia Broad nonseptate hyphae, sporangia.Widespread in environment; found in decaying vegetables and fruits, soil, old bread; grow and sporulate on materials containing carbohydrates. R. oryzae is most common clinical isolate.
44 Mucormycosis - Clinical features Rhinocerebral/craniofacial mucormycosisInfection of paranasal sinuses with extension from ethmoid into orbit or frontal lobe (also cavernous sinus thrombosis).Prompt diagnosis essential; direct exam of turbinate scrapings and/or sinus aspirate.PneumoniaResembles invasive pulmonary aspergillosisCutaneous infectionAssociated with localized traumaCellulitis with central necrotic area.