KINGDOM FUNGI

Introduction to FungiA large and diverse group ranging from a single-celled yeast or filamentous mold to a fleshy mushroom

Include some of the most important organisms, in terms of ecological and economic roles

Their ability to breakdown dead organic material allow continuation of the cycle of nutrients through ecosystem

Introduction to FungiSymbiotic fungi, which inhabit plant roots, supply essential nutrients to most vascular plants

Mycology

The branch of microbiology that studies fungi

General Characteristics of FungiHeterotrophic

Use organic compounds as carbon source

Nonphototrophic

Do not use light as energy source

Absorptive

Take up nutrients in solution

Saprophytic

Obtain nutrients by decomposing deal organic matter

Morphology of FungiYeasts

Single-celled form of fungusDo not have chlorophyllAble to reproduce by buddingSometimes, the bud remains with the mother cell and produces a pseudohyphaForm round, pasty or mucoid colonies with a pleasant odor, when on solid media

Morphology of FungiMolds

Highly branched and loosely intertwined hyphae that form a myceliumMycelia form woolly growth on damp and decaying material in nature and fuzzy spreading colonies on solid culture media

Morphology of FungiMycelium

A mass of hyphaecoenocytic--undividedsepta--incomplete divisionsThallus

body of the fungus Consists of long interconnected filamentsHyphae

individual filaments

FUNGAL HYPHAE

Coenocytic (undivided) hypha

Septate hypha

septum

Morphology of FungiDimorphism

Fungi are able to grow either as a mold or as a yeast

In pathogenic fungi, it is temperature-dependentYeastlike at 37CMoldlike at 25CMucor sp.

Morphology of FungiFleshy fungi

Form the fruiting structures Consist of tightly intertwines hyphaeEx: mushrooms, truffles or shelf fungi

Reproduction of FungiAssexual

elongation and fragmentationbuddingasexual spores Formed by the hyphae of one organismGenetically identical to the parent

Sexual

sporesResult from the fusion of nuclei from two opposite mating strains of the same species of fungus

Types of Asexual SporesConidia

Uni- or multicellular spores that are not enclosed in a sacEx. Aspergillus

Arthrospores

Formed by the fragmentation of a septate hypha into single, slighlty thickened cellsEx. Coccidioides immitis

Blastoconidia

Consists of buds coming off the parent cellEx. Candida albicans and Cryptococcus

Types of Asexual Spores

Chlamydospores

Thick-walled spores formed by rounding and enlargement within a hyphal segmentEx. Yeast form of C. albicans

Sporangiospores

Formed within a sac (sporangium)Each sporangium can contain hundred of sporangiosporesEx. Rhizopus

Sexual reproductionSexual spores results from sexual reproduction, consisting of three phases:

PlasmogamyHaploid donor cell nucleus (+) penetrates cytoplasm of recipient cell ()

Karyogamy+ and nuclei fuse

MeiosisDiploid nucleus produces haploid nuclei (sexual spores)

Sexual SporesZygospore

Fusion of haploid cells produces one zygospore

Ascospore

Formed in a sac (ascus)

Basidiospore

Formed externally on a pedestal (basidium)

Divisions of FungiThe Lower Fungi

All are coenocytic and lack septaChytridiomycetes and Zygomycetes

The Higher Fungi

All are septated, terrestrial, and have nonmotile conidia and gametesAscomycetes, Basidiomycetes and Deuteromycetes

Basis for ClassificationSexual reproduction

Shape and internal structure of the sporangia

The structure which produce the sporesMost useful characteristic for identification

LOWER FUNGI

ChytridiomycetesWater molds with uniflagellated sporangiospores and gametesGrow as fuzzy, whitish masses on organic materials in streams or pondsSometimes classified under Protista

Ex. Allomycesgrows in tropical ponds and streamsproduce beautiful bright orange sporangia

OomycetesForm the cottony masses on dead algae and animals in freshwaterFunction as decomposersAsexually, resemble the zygomycete fungi

Produce nonmotile female gametes and sexual spores (zoospores)Produce biflagellate sporangiospores and male gametes

Traditionally classified under fungi due to its structure

However, Its cellulose cell wall and DNA analysis confirmed its close relation to other algae

OomycetesSaprolegnia sp.

Parasite of fishesPhytophthora infestans

Causative agent of the great potato blight of Ireland

ZygomycetesTerrestrial molds

Able to complete their life cycle with minimal moisture Produce nonmotile sporangiospores and zygospores

Rhizopus (black mold)

Usually develops on stale bread Has a life cycle typical of ZygomycetesCauses zygomycoses, which attack immunocompromised individuals

HIGHER FUNGI

Ascomycetes

Produce sexual spores called ascosporesThe spores undergo several meiotic division producing haploid ascospores within an ascus

Morchella spp. (Morel)

Mushrooms with globular heads on stalkKnown for its delicious taste

Aspergillus

Causes opportunistic and systemic mycosesBlastomyces dermatitidis, Histoplasma capsulatum

Causes systemic mycosesMicrosporum, Trichophyton

Causes cutaneous mycosesMorchella sp.

Basidiomycetes

Produce sexual spores called basidiosporesUsually form basidiocarpsCommonly known as club fungi, mushrooms, puffballs or shelf fungiHave unique phase in their life cycle called dikaryon

A mycelium that contains two different kinds of nuclei (one from each parent)

DeuteromycetesDo not produce sexual sporesProduce conidia onlyGrow as molds or yeastsAlso known as Fungi Imperfecti

Due to lack of sexual stageMany species can cause human diseases

Blastomyces, Cryptococcus, Histoplasma, and CandidaAspergillusPenicillium

MycosesAny fungal infectionGenerally chronic infection due to the slow growth of fungi

Classification of mycoses is based according to:

Degree of tissue involvement Mode of entry into the host

Four groups of mycoses

Systemic, Subcutaneous, Cutaneous, Opportunistic

Systemic MycosesFungal infection deep within the bodyCan affect a number of tissues and organsUsually caused by terrestrial fungiTransmission is through inhalation of sporesInfection typically starts in the lungs, then spread to other body tissues

Ex. Coccidioidomycosis, Histoplasmosis

Coccidioidomycosiscocci, desert fever, desert rheumatism, desert bumps

Etiologic agent: Coccidioides immitisA dimorphic fungusAsexual spores: arthrosporesSexual spores: endospores

Endemic in southwestern United States, and Central and South AmericaConsidered as a potential biological weapon

Histopath showing endospore

CoccidioidomycosesThree clinical forms:

Primary pulmonarySigns and symptom: flu-like with rashes (erythema multiforme)If the disease does not progress, the individual develops resistance for 20 years to a lifetime

Benign formHallmark: development of well-defined lung cavitationMay be subclinical for years

Disseminated formDevelops in very few individualsSpread to various internal organs, including the brain

HistoplasmosisEtiologic agent:

Histoplasma capsulatum

A dimorphic fungusMycelial form:

produces microconidia (spores)

Found worldwideMode of transmission:

inhalation of spores Yeast formMycelial form

HistoplasmosisThree clinical forms:

Primary acuteMay be asymptomatic or may develop flu-like symptomsOther symptoms: chest pain, shortness of breath, hoarseness

Chronic cavitaryRelatively large pulmonary lesions developWith little signs and symptomsOften mistaken for tuberculosis

Severe disseminatedOccur most often in immunocompromised patientsOften fatal

Subcutaneous MycosesFungal infection beneath the skin caused by saprophytic fungi that live in soil and on vegetation

Infection occurs by direct implantation of spores or mycelial fragments into a puncture wound in the skin

Sporothrichosis

Gardeners diseaseA chronic subcutaneous mycosis with eventual lymphatic involvementIf untreated, may become a generalized infection involving bones, joints and other internal organsA relatively common disease with predilection to horticultural workers

Subcutaneous MycosesSporothrichosis

Etiologic agent: Sporothrix schenckiiA dimorphic fungus that commonly inhabits the soil and the epidermis of plantsAcquired through a scratch from a thorny plant, forcing the fungus into the subcutaneous tissues

Clinical presentation:From a small, movable, subcutaneous nodule, it spread to the lymph vessels of arm Open lesions are prone to secondary bacterial infection

Cutaneous Mycoses (Dermatomycoses)Fungi that infect only the epidermis, hair and nailsKnown as dermatophytes, which secrete keratinaseTransmission is from human to human or from animal to human by direct contact Transmission also by contact with infected hairs and epidermal cells

Causative agents:

Microsporum, Epidermophyton, TrichophytonMonomorphic fungi cultures at room temperture using Sabourauds mediumIdentification is based on gross and microscopic morphology of the colony

Some Clinical Forms of DermatomycosesTinea capitisTinea barbaeTinea ungiumTinea corporisTinea pedisTinea cruris

MicrosporumInfect hair and skin onlyForm both macro- and microconidia on short conidiophoresMacroconidia:

Multiseptate, fusiform, spindle- to oval shaped, cell walls vary in thickness and textureImportant for species identificationMicroconidia:

Single-celled, pyriform and smooth-walled, and are not diagnostic for any species

Common species

M. canis causes ectothrix hair and skin infectionM. ferrugineum causes tinea capitis; its branching hyphae has prominent cross walls, which gives it the characteristic bamboo hyphaeM. gypseum causes tinea barbae, ectothrix infectionM. canisM. ferrugineumM. gypseum

EpidermophytonInfect skin and nails only

Epidermophyton floccosum

the only species that infect man

Cause infection of the groin, body, feet and nailsMacroconidia:

club-shaped; singly or in clumps of 2 or 3; smooth cell wall; with 2-5 septaNo microconidia are formed

TrichophytonInfects the skin, hair or nailsInfect man and other animalsCharacterized by smooth-walled macro- and microconidia

Only a few species form macroconidia

Macroconidia are mostly directly attached on hyphae and fusiform in shape

Microconidia

Mostly spherical to pyriform or of irregular shape

Common species of TrichophytonT. concentricum

Commonly produce characteristic circular skin lesions tinea umbricata, a form of tinea corporisChlamydoconidia (in old culture) show typical balloon-shape

T. mentagrophytes

Cause of athletes footAlso cause tinea capitis, tinea corporis, tinea barbae and tinea crurisForm numberous, round microconidia, often in grape-like clusters

Common Species of TrichophytomT. rubrum

cause long-established foot and toenail infection, which is difficult to eradicateMay also cause tinea corporis and tinea capitisMicroconidia are thin-walled, cigar-shaped

T. tonsurans

Causes endothrix hair infections The entire hair shaft seems to be filled with sporesCauses tinea capitis, tinea corporis and tinea pedisMicroconidia are abundant, club-shaped and attached on the hyphae

Opportunistic PathogensMode of transmission:

Spores inhaled by people with debilitating lung diseases or cancerA granulomatous, necrotizing disease of the lungs, which often disseminate hematogenously to various organsMicroscopic exam:

Hyaline, septate hyphae with dichotomous branchingNo yeast observedGenerally harmless, but can become pathogenic in immunocompromised host

AspergillosisCausative agent: Aspergillus fumigatus

Opportunistic PathogensMucormycosis

phycomycosis or zygomycosisCaused mostly by Rhizopus and MucorInfection occurs mostly in patients with diabetes mellitus, leukemia or those undergoing immunosuppressive therapyMicroscopic exam: Large, hyaline, coenocytic hyphae

Candidiasis

moniliasis, mycotic vulvovaginitis, thrushCaused by Candida albicansA normal flora of the GI tract, vagina and oral areasIn room temperature, favors yeast form, which reproduce by buddingInside the human body, may develop a pseudohyphaeFrequently occurs in newborn, AIDS patient and those on broad-spectrum antibiotic

Cryptococcosisacute or chronic, pulmonary, systemic or meningeal mycosis genus: Cryptococcus (C. neoformans)Encapsulated yeastGrows in soil; from pigeon droppings no.2 cause of deaths in AIDS in ThailandMonomorphic

ToxinsSome fungi produce toxins that are hallucinogenic or poisonous

Muscarin

Produced by Amanita muscaria mushroomHighly hallucinogenicConsumed as part of the religious rites of people native to the northern rim of the Pacific Ocean

Phalloidin and amanitin

Produced by A. phalloides mushroom (death cap)Highly poisonousIngestion of a small queantity can cause death from irreversible liver failureA. muscariaA. phalloides

ToxinsErgot

Produced by Claviceps purpureaA mold that grows on rye which produces highly toxic ergotSt. Anthonys fire (ergot poisoning)Manifested by disorientation, hallucination, gangrene, abortion or deathErgot derivative drugs include methergine

ToxinsAflatoxin

Produced by Aspergillus flavusFrom not properly dried crops, such as peanuts and cereal grainscan cause severe liver damage and deathEven low levels may be carcinogenic

Black mold toxin

sick building syndromeStachybotrys chartarum in damp buildingscan manifest as headaches, dermatitis and general malaise