Page 408 - Review of Medical Microbiology and Immunology ( PDFDrive )

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PART V MYCOLOGY

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P
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C
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Basic Mycology

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CHAPTER C ONTENT S
Structure & Growth
Pathogenesis
Self-Assessment Questions
Fungal Toxins & Allergies
Practice Questions: USMLE & Course Examinations
Laboratory Diagnosis

STRUCTURE & GROWTH

Fungi
Because fungi (yeasts and molds) are eukaryotic organ-
isms, whereas bacteria are prokaryotic, they differ in sev- TABLE 47–1 Comparison of Fungi and Bacteria
Approximately
Diameter
Approximately 1μm
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eral fundamental respects (Table 47–1). Two fungal cell
(Staphylococcus)
4 μm (Candida)
structures are important medically:
Prokaryotic
Eukaryotic
Nucleus
(1) The fungal cell wall consists primarily of chitin (not
endoplasmic
endoplasmic
peptidoglycan as in bacteria); thus fungi are insensitive to
reticulum
reticulum absent
certain antibiotics, such as penicillins and cephalosporins,
present
that inhibit peptidoglycan synthesis.
Sterols present
Sterols absent (except
Cell membrane
(2) Chitin is a polysaccharide composed of long chains
Mycoplasma)
of N-acetylglucosamine. The fungal cell wall contains other
Cell wall
Chitin
Peptidoglycan
polysaccharides as well, the most important of which is
content
β-glucan, a long polymer of d-glucose. The medical impor-
Endospores for survival, not
Sexual and asexual
Spores
tance of β-glucan is that it is the site of action of the anti-
for reproduction
spores for
fungal drug caspofungin.
reproduction
(3) The fungal cell membrane contains ergosterol, in
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contrast to the human cell membrane, which contains cho-
dimorphism
lesterol. The selective action of amphotericin B and azole
Metabolism
Many do not require
Require organic
drugs, such as fluconazole and ketoconazole, on fungi is
carbon; no
based on this difference in membrane sterols.
obligate
many obligate anaerobes
anaerobes
There are two types of fungi: yeasts and molds. Yeasts
grow as single cells that reproduce by asexual budding.
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