LESSON 4: LABORATORY METHODS FOR ISOLATION AND IDENTIFICATION OF MEDICALLY IMPORTANT YEAST Flashcards
Eukaryotic, unicellular fungi
- Reproduces by budding
- Moist or waxy colonies
- Round to oval, or less often
- Elongate or irregular shape
Yeast
Cell wall of yeast: ___________
Chitin; also Glucans and Mannans
Cell membrane of yeast: _____________
Ergosterol
- Primary isolation medium for yeast
a. Sabouraud Dextrose Agar (SDA)
- Acidic pH (5.0) inhibits growth of
bacteria
a. Sabouraud Dextrose Agar (SDA)
- High concentration of sugar
a. Sabouraud Dextrose Agar (SDA)
inihibits bacteria
Chloramphenicol
inhibits saprobes
Cycloheximide
- Selective medium for isolation of fungi
b. Mycosel Agar (SDA with Chloramphenicol and
Cycloheximide)
- Screening test used to differentiate
Candida albicans and Candida dubliniensis from
other yeast
Germ Tube
Tests the ability of the yeast to produce
tube-like projections from a conidia or spore in
human serum or fetal bovine serum after 2-3
hours of incubation at 37°C
Germ tube
- Corn meal with Tween 80 Agar Test
Morphology Studies (Dalmau Plate Method)
For distinguishing various species
Candida spp. and other yeasts
Morphology Studies (Dalmau Plate Method)
is added to
cornmeal agar to reduce the surface tension to allow for the development of pseuodhyphal,
hyphal, blastoconidial growth, chlamydospores,
and arthroconidia
Polysorbate (Tween) 80
Used in the identification of different
yeasts
Urease Test
Same as used in bacteriology
Urease Test
urease test color when positive
intense pink color
urease test color when negative
no color change
Determines the ability of a yeast isolate
to use a particular carbohydrate substrate as its
sole carbon in a medium
Carbohydrate Assimilation Test (CAT)
- For precise identification of frequently
encountered yeasts
Carbohydrate Assimilation Test (CAT)
- Identification is obtained through
Analytical Profile Index or using Identification
Software
Carbohydrate Assimilation Test (CAT)
- Composed of 20 cupules for 19
assimilation tests
API 20°C AUX
are inoculated with semisolid minimal medium
cupules
___________ will grow if they are capable of
utilizing each substrate as the sole carbon source
yeast
Reactions are read by comparing to
growth control
API 20°C AUX
Test use for API 20 degrees C AUX
Carbohydrate Assimilation Test
Incubations of API 20°C AUX
29°C ± 2°C for 48-72 hours
Limitations for API 20°C AUX
Intended uniquely for ID of
yeast including in its database (44 species)
- Determines the ability of a yeast to
degrade a specific carbohydrate
Carbohydrate Fermentation Test (CFT)
- ___________is demonstrated by
production of gas
Fermentation
- Useful when other tests fail to identify
the isolate
Carbohydrate Fermentation Test (CFT
Carbohydrate Fermentation test positive color
Green
Carbohydrate Fermentation test negative color
yellow
- Used for isolation and differentiation of
clinically significant Candida spp.
Chromogenic Agar
-__________, ________, ________ produce different colors
Colonies of C. albicans, C. tropicalis, and
C. krusei
CGB means
L-Canavanine, Glycine,
Bromothymol Blue
Used for the differentiation of:
- Cryptococcus gattii vs
Cryptococcus neoformans
CBG
