Intro To Myco Microbiology Iusm

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**there are more flashcards to come!

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more flashcards to come!

Front 2

are fungi eukaryotic or prokaryotic?

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eukaryotic
- a lot like humans

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what are key characteristics of bac?

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1. Nuclear membrane absent
2. Single, naked chromosome
3. Peptidoglycan in the cell wall
4. Small, simple ribosomes
5. STEROLS ABSENT (except Mycoplasma)
6. Rapid growth (generation times are usually 15-30 minutes)

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what are key characteristics of fungi?

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1. Nuclear membrane present
2. Multiple chromosomes
3. Many organelles
4. GLUCAN and CHITIN in the cell wall
5. Eukaryotic ribosomes
6. Sterols in the cell membrane
(ERGOSTEROL)
7. SLOW growth- long generation times which may be several hours
1. They resemble mammalian cells
2. Cell wall has chitin (glucosamine), hexose, hexosamine, protein etc.
3. Special stains may be required
to see them

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what are some antifungal agents?

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polyenes
imidazoles
echinocandins

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what's polyene's target? drug exs? static or cidal?

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target is ergosterol in the cell membrane; example: Amphotericin B (Lipid-coated Polyene)- target is ergosterol; example: AmBisome; fungicidal

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what's imidazole's target? drug exs? static or cidal?

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target is synthesis of ergosterol; examples voriconazole, itraconazole; fungistatic

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what's echinocandin's target? drug exs? static or cidal?

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target is glucan synthetase; example: Caspofungin; esp. Candida (-cidal) and Aspergillus (-static)

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list fungi morphology:

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Yeast
Yeast-like
Mold (hyphae)
Dimorphic Fungi

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list yeast characteristics:

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1. Round or oval fungi that bud or pinch off; some make pseudohyphae
2. Growth resembles bacteria
3. May be dry, pasty or slimy
4. May be Gram-positive
5. Much larger than bacteria- bacteria are 0.1-0.2 microns; yeasts are 3-20 microns (the size of PMNs, RBCs, etc.)

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what 2 types of fungi can mold be?

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Filamentous or Hyphal Fungi

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what does mold look like?

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1. Seen microscopically as
filaments which are variable in
length, but usually constant in
diameter
2. On plates they look fuzzy or
“carpet-like)

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what are 4 stages of hyphae?

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septate
aseptate
vegetative
aerial

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describe septate hyphae:

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filaments have crosswalls or septae

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describe aseptate hyphae:

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filaments lack crosswalls; also called coenocytic

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describe vegetative hyphae:

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growth within the surface of the medium (agar)

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describe aerial hyphae:

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filaments that extend above the surface (stick up into the air)

Front 18

how does temp affect fungi type?

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1. In human tissue and when grown at 37 C the fungus appears to be yeast or yeast-like
2. In nature and when grown at room temperature (23 C) the fungus produces hyphae

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what fungi phase is infectious?

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Mold Phase- infectious (conidia)

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what fungi phase isn't infectious?

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4. Yeast Phase- seen in tissue but this form is not infectious or communicable, so no isolation is required for the patient

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how does fungi reproduce?

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sexually
asexually

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what's known about fungi sexual reproduction?

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Used for scientific classification
Rarely seen in tissue
Not usually studied in the laboratory
Probably not infectious

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what's known about fungi asexual reproduction?

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1. These are the forms we study in the lab
2. Asexual reproductive forms are called CONIDIA
3. Sometimes called spores- they are not spores
4. Usually round but may be rectangular
5. Similar in size to yeasts

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what are the 3 special types of conidia?

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Blastoconidia
Arthroconidia
Chlamydoconidia

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describe Arthroconidia?

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. Hyphae break or fragment at
separation points forming small
pieces that give rise to new
hyphae

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give exs of arthroconidia:

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Coccidioides,
Geotrichum

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give blastoconidia facts:

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1. Cells reproduce by budding
2. Daughter cells pinch off from the
mother cell
3.Note: If blastoconidia continue to
elongate and fail to pinch off, they are called pseudohyphae (yeast-like)

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give blastoconidia exs:

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Candida,
Cryptococcus

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give chlamydoconidia facts:

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1. Round and thick-walled conidia
that form directly within or at the ends of hyphae; they can then
fragment or break off to form new hyphae

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give chlamydoconidia exs:

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Candida albicans
dermatophytes

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extra types of conidia?

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Macroconidia
Microconidia
Arrangement of conidia

Front 32

what are the special stains for fungi?

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Giemsa
GMS
PAS
Calcofluor

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describe giemsa stain:

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nucleus blue with clear or pink cytoplasm

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describe GMS stain:

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(Gomori’s Methenamine Silver) or
Silver Stain- yeasts and hyphae are brown-black; the counterstain is usually green; stains the cell wall only

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describe PAS stain:

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(Periodic Acid Schiff)- stains cell
walls pink; counterstain is blue or green

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describe Calcofluor stain:

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fluorescent stain (glucans/chitin)

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why are we seeing more mycoses today?

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1. More compromised patients
2. Transplant patients
3. Anti-cancer drugs
4. Invasive catheters (bladder, CNS, vascular)
5. Use of broad-spectrum antibiotics
6. The host has changed, not the fungi

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how do ppl get mycoses?

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1. Overgrowth of normal flora (usually Candida) after catheters,
chemotherapy or broad spectrum antibiotics
2. Inhalation of conidia (Histoplasmosis)
3. Trauma/implantation (Sporothrix)
4. Contact with plants (Sporothrix) and animals (dermatophytes)

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how do we diagnose mycoses?

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1. Direct observation in patient tissue
2. Laboratory culture and morphologic identification
3. I.D. by biochemical or assimilation tests
4. I.D. by molecular methods (DNA Probe)
5. Serologic evidence of infection- CF,ID or other

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what are general char of dermatomycoses?

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1. Hair, skin and nails involved
2. Most common of all fungal
infections
3. Keratin metabolized as a
nitrogen source
4. Deep invasion is RARE

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describe tinea infec:

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1. Tinea is latin for worm
2. Outer “ring” is red and is the
expanding infection
3. Inner area is pale with healing
4. Tinea corporis (body),
pedis (foot), cruris (groin),
capitis (head), unguium (nail)

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how do you examine tissue for fungi?

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1. KOH- potassium hydroxide
destroys skin, nail, hair and
leaves hyphae or yeast visible
2. Calcofluor White- fluorescent stain for fungi
3. Tissue biopsy with special stain (PAS, GMS) when the clinical impression is unclear

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how do you culture and identify fungi?

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1. Primary Isolation Media-
Mycobiotic agar or similar
medium; few conidia produced;
CYCLOHEXAMIDE added to kill
contaminants (Aspergillus etc.)
2. Subculture for conidia production; cornmeal, potato dextrose

Front 44

what are some superficial mycoses?

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Tinea versicolor
Tinea nigra (palmaris)
Black piedra
White piedra

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describe tinea versicolor:

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1. Malassezia furfur
2. Lipophilic yeast-like (olive oil req.)
3. Hyper- or hypopigmentation
4. Spaghetti (hyphae) and meatballs (yeasts) on direct smear
5. Treat with selenium (dandruff shampoo)

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what does tinea nigra do? species?

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(palmaris)- black color on palm; Hortaea werneckii

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what does piedra hortae do? species?

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(black piedra); black hair spots; Piedria hortae

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what does white piedra do? species?

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white hair spots; Trichosporon beigelii

Front 49

what are some cutaneous mycoses? (dermatomycoses)

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Dermatomycoses
Dermatophytoses
Ring Worm
Tinea

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what are the species that cause dermatophytoses?

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1. Epidermophyton floccosum
2. Microsporum canis
3. M. gypseum
4. M. audouinii
5. Trichophyton tonsurans
6. T. rubrum
7. T. mentagrophytes

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how do you culture dermatophytes?

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1. Sabouraud’s Agar- all fungi
2. Mycobiotic Agar- Cyclohexamide added to kill skin contaminants
3. Incubation time 2-4 weeks
4. Often fluffy white growth

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how can you identify trichophyton?

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1. Microconidia important for
identificatiom
2. Macroconidia rarely helpful
3. Biochemical tests available

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what types of infec does trichophyton usually cause?

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Usually feet and nail infections

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how do you identify T. rubrum?

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1. Colonies white and fluffy or
granular
2. Cherry red on reverse (3 wks)
3. Tiny teardrop microconidia;”birds on a fence”
4. Urease (-)
5. Hair perforation (-)

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how do you identify T. mentagrophytes?

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1. Colonies- 2 types: downy from
feet; granular from infections spread by animals
2. Reverse may be red/brown
3. Microconidia in grape-like clusters; cigar macroconidia
4. Urease (+)
5. Hair perforation (+)

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what's the #1 cause of tinea capitis?

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T. tonsurans

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how do you identify T. tonsurans?

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. Buff/brown colonies often
wrinkled or cratered
3. Microconidia like elongate
baloons or stretched teardrops
4. Grows poorly on most media
5. Growth enhanced by thiamine

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describe epidermophyton:

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1. Single species
2. Large, club-like macroconidia
3. No microconidia

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how can you identify E. floccosum?

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2. Olive green to khaki colonies
3. Macroconidia are smooth and
THIN-WALLED; club-shaped
and multicelled; in 2’s and 3’s
4. No microconidia

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what does E. floccosum infect?

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groin
feet

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what kills E. floccosum?

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refrigeration!

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how do you identify Microsporum?

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1. Macroconidia are used for
identification
2. Microconidia produced but not
useful in identification
3. Biochemical and other tests
not generally useful

Front 63

what's the #1 fungi infec in dogs and cats?

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M. canis

--then they give it to humans!

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how do you identify M. canis?

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3. Yellow/green fluorescence
with Woods lamp
4. Ectothrix hairs (outside)
5. Colonies fluffy or granular;
bright yellow on reverse
6. Walls of macroconidia are thick
and rough
7. Macroconidia have 8-15 cells
and show a curved tip

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how do you identify M. gypseum?

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2. Infected hairs do not fluoresce
3. Ectothrix hairs
4. Powdery, cinnamon-colored
colonies; orange/brown on
reverse
5. Ellipsoidal macroconidia have
rounded (blunt) ends
6. Macroconidia cell wall is thin
7. Macroconidia have 2-7 cells

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what type of fungus is M. gypseum?

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Soil fungus; rare in humans

Front 67

how do you identify M. audouinii?

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Yellow-green on Woods lamp
3. Slow grower; light gray
colonies with pink reverse
4. Conidia are usually not seen
5. Racquet or antler hyphae

Front 68

what's 2nd most common cause of tinea capitis?

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M. audouinii