Transcript Dimorphic fungi

Medical Mycology
1
Comparison of fungi and bacteria
Feature
Fungi
Bacteria
diameter
4 µm
1 µm
nucleus
eukaryotic
prokaryotic
cytoplasm
with mitochondria and without mitochondria and
endoplasmic reticulum 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
2
3
4
5
6
7
Role of fungi in nature
There are approximately 70,000
recognized species of fungi.
Most are beneficial to humankind.
production of food
antibiotics and immunosuppressive drugs
used as model systems in molecular
biology
8
Medical Mycology
the 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.
9
曲霉菌
假丝酵母菌
表皮癣菌
小孢子癣菌
毛癣菌
Mucor 毛霉菌
Cryptococcus neoformans 新型隐球菌
皮炎芽生菌
荚膜组织胞浆菌
巴西副孢子菌
10
Cellular Morphology
Yeasts: unicellular organisms
mycelia (molds): multicellular
Dimorphic fungi
11
12
13
A. Yeast cells propagating by blastoconidia / budding
B. Yeast dividing by binary fission
C. Development of pseudohyphae
14
molds
15
• a mold is multicellular microbes composed of two
parts: spore and hypha.
Hypha
spore
16
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 ℃.
17
Culture & Colony morphology
Sabouraud culture medium.
Optimal pH 4-6.
Optimal temperature 22-28 ℃, 37 ℃ for
certain pathogenic fungi.
Aerobic.
18
Unicellular fungi
19
Multicellular fungi
20
Resistance
• Fungi have strong resistance to dryness, sunlight, UV light
and many chemical agents, but much sensitive to wet heat.
21
Drugs
• 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.
22
Clinical Manifestations
23
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).
24
Anti-fungus Immunity
& fungal Infectious diseases
25
•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
26
A. Superficial mycoses:
Infections are limited to the hair or the outermost layers of skin.
27
28
29
30
31
32
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).
33
34
•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
35
common cutaneous mycoses:
36
37
C. Subcutaneous mycoses:
The infections involve the dermis, subcutaneous tissue, muscle
and fascia.
38
39
40
41
42
43
D. Systemic mycoses:
the infections originate primarily from the lung and then
spread to many other organs
44
Cryptococcus neoformans
Oval, budding yeast surrounded by
characteristic thick polysaccharide
capsule.
45
C. neoformans with capsule is negatively stained by India Ink
46
Disease
Cryptococcosis
Acute or chronic infections in the lung,
bone and skin, and meningitis
meningitis can last several months and are
highly fatal
No human to human transmission
Infection follows inhalation of pigeon or
chicken droppings containing the microbe
47
Opportunistic mycoses
Patients or individuals with immune
deficiency are easily suffering from
opportunistic mycoses caused by fungi
belonging to normal flora.
48
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.
49
50
Pseudohyphae and hyphae of Candida albicans using
Methenamine Silver Stain.
51
Oral thrush is a typical and common disease caused
by Candida albicans
52