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Medical MycologyMedical Mycology

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Comparison of fungi and bacteria

Feature Fungi Bacteria

diameter 4 µm 1 µm

nucleus eukaryotic prokaryotic

cytoplasm with mitochondria and endoplasmic reticulum

without mitochondria and endoplasmic reticulum

Cell membrane

sterol present sterol absent

Cell wall chitin peptidoglycan

spores sexual and asexual spore for proliferation

spore for survival, not for proliferation

dimorphism yes No

metabolism Require organic carbon and no anaerobes

May do not require organic carbon and maybe anaerobes

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Role of fungi in natureThere are approximately 70,000 recognized species of fungi.Most are beneficial to humankind.

production of foodantibiotics and immunosuppressive drugsused as model systems in molecular biology

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Medical Mycologythe subject on pathogenic fungi

Some fungi act as the plant and animal pathogens in the agricultural industry. About 300 species of fungi cause human infections.

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表皮癣菌

毛癣菌小孢子癣菌

新型隐球菌

荚膜组织胞浆菌

皮炎芽生菌

巴西副孢子菌

假丝酵母菌曲霉菌

毛霉菌Mucor

Cryptococcus neoformans

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Cellular Morphology

Yeasts: unicellular organisms mycelia (molds): multicellularDimorphic fungi

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A. Yeast cells propagating by blastoconidia / buddingB. Yeast dividing by binary fissionC. Development of pseudohyphae

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molds

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• a mold is multicellular microbes composed of two parts: spore and hypha.

Hypha

spore

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Dimorphic fungi

• Some fungi exist in both yeast and mycelial forms.

These fungi are called dimorphic fungi.

Yeast form: a parasitic or pathogenic form.

This form is usually seen in tissue of patients. Can

be cultured at 37 ℃. Conversion to yeast form

appears to be essential for pathogenicity.

Mycelial form: a saprophytic form. This is the

form existing in nature. Can be cultured at 25 ℃.

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Culture & Colony morphologyCulture & Colony morphology

Sabouraud culture medium.

Optimal pH 4-6.

Optimal temperature 22-28 ℃, 37 ℃ for

certain pathogenic fungi.

Aerobic.

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Unicellular fungi

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Multicellular fungi

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• Fungi have strong resistance to dryness, sunlight,

UV light and many chemical agents, but much

sensitive to wet heat.

Resistance

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• The antibiotics to treat fungal infectious diseases

are quite different compared to those to cure

bacterial infectious diseases: amphotericin B ( 两性霉

素 B), anticandine ( 制霉菌素 ), miconazole ( 咪康唑 ),

ketoconazole ( 酮康唑 ) etc.

Drugs

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Clinical Clinical ManifestationsManifestations

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Major clinical manifestations of fungal diseases:

◇Hypersensitivity ： an allergic reaction to molds and spores.

◇Mycotoxicosis: poisoning of human and animals by food contaminated with mycotoxins.

◇Infectious diseases: caused by exogenous pathogenic fungi or endogenous fungi (opportunistic infections).

◇Inducing tumors: Some mycotoxins can induce tumors (e.g., aflatoxin causes liver cancer) ( 黄曲霉素 ).

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Anti-fungus ImmunityAnti-fungus Immunity& & fungal Infectious fungal Infectious

diseasesdiseases

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•In general, humans have a high level of innate

immunity to fungi and most of the fungal

infections are mild and self-limiting.

•For the exogenous pathogenic fungi, the

infections are classified according to where the

infections take place:

A. Superficial mycoses

B. Cutaneous mycoses

C. Subcutaneous mycoses

D. Systemic mycoses

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A. Superficial mycoses:

Infections are limited to the hair or the outermost layers of skin.

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B. Cutaneous mycoses:

• Fungi invade the keratinized layers ( 角化层 ) of skin, hair and nails and the diseases are limited

in these layers.

• The fungi causing these diseases are termed dermatophytes ( 皮肤癣真菌 ).

• The diseases are referred to as tinea ( 癣病 ).

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•All tinea are caused by members of three genera:

Trichophyton ( 毛癣菌 )Epidermophyton ( 表皮癣菌 )

Microsprum ( 小孢子癣菌 )

•Unlike the superficial mycoses, cellular immune responses may be evoked

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common cutaneous mycoses:

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C. Subcutaneous mycoses:

The infections involve the dermis, subcutaneous tissue, muscle and fascia.

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D. Systemic mycoses:

the infections originate primarily from the lung and

then spread to many other organs

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Cryptococcus neoformans

Oval, budding yeast surrounded by characteristic thick polysaccharide capsule.

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C. neoformans with capsule is negatively stained by India Ink

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DiseaseCryptococcosis

Acute or chronic infections in the lung, bone and skin, and meningitismeningitis can last several months and are highly fatal

No human to human transmissionInfection follows inhalation of pigeon or chicken droppings containing the microbe

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Opportunistic mycosesPatients or individuals with immune deficiency are easily suffering from opportunistic mycoses caused by fungi belonging to normal flora.

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Candida albicans can be found in 40-80% of normal human beings. It is present in mouth, intestine and vagina. Candida albicans is dimorphic fungus. Candida albicans can show germ tubes with special shape, which used as a diagnostic feature of the microbe.

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Pseudohyphae and hyphae of Candida albicans using Methenamine Silver Stain.

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Oral thrush is a typical and common disease caused by Candida albicans