MycologyLabProceduresSummer20 importance12.ppt

Mycology: Lab Methods
Collection of specimens:
 Skin specimens - clean with 70% alcohol to remove dirt,
oil and surface saprophytes.
 Nails - cleaned same as skin. Usually clipped; need to
be finely minced before inoculating to media.
 Hair - obtained from edge of infected area of scalp; hair
can be obtained by plucking, brushing, or with a sticky
tape. A Wood’s lamp can be helpful in locating infected
areas.
 Body fluids - normal sterile collection procedures.

Preparation of specimens for transport:
 Hair & nails sent in a dry envelope, inside proper
container.
 Other specimens are usually sent frozen or on dry ice.
 Packaging - must meet biohazard regulations. Cultures
must be on tubed media (not plates).
 Inside labeling information: patient ID, specimen source,
suspected organism.

Outside labeling - WARNING: POTENTIAL PATHOGEN

Processing of specimen to recover fungus:
 Skin, nails, & hair - direct exam following KOH
preparation.
 Body fluids -
 CSF - centrifuged; examine sediment
microscopically, inoculate media.
 Pleural fluid, sputum, and bronchial aspiration -
specimen must be fresh as saprophytes would
overgrow pathogens such as H. capsulatum.
Specimens may be refrigerated up to 2 hours.
 Gastric washings - same as for pleural fluids.

Processing of specimen to recover fungus:
 Body fluids - (continued)
 Genito-urinary specimens - first morning specimen
preferred; centrifuge & inoculate on media.
 Blood/bone marrow - inoculate to BHI broth and BHI
slant.

Wound abscess or drainage - culture anaerobically if
actinomycosis is suspected.
 Tissue specimens - examine for pus, caseous material
or granules; mince aseptically, inoculate on media.

Direct examination of specimens:
 Direct exam required on any biological material sent to
lab for fungus culture. Examine for spores, hyphae,
mycelial elements, budding yeast, mycotic granules.
 Wet mount - good for yeast; examination is done in
natural environment, so loss of fragile structure is
minimal.
 KOH - done on skin scrapings, hail, nails, sputum,
vaginal specimens. KOH clears tissue cells so fungal
elements may be seen.

Stains used:
 Lactophenol Cotton Blue - very popular for quick
evaluation of fungal structures; stains chitin in
cell walls of fungi.
 Periodic Acid - Schiff Stain (PAS) - stains
polysaccharide in the cell wall of fungi. Fungi
stain pink-red with blue nuclei.
 Gomori Methenamine Silver Stain - silver nitrate
outlines fungi in black due to the silver
precipitating on the fungi cell wall.

Stains used: (continued)
 Gridley Stain - Hyphae and yeast stain dark blue or rose.
Tissues stain deep blue and background is yellow.
 Mayer Mucicarmine Stain - will stain capsules of
Cryptococcus neoformans deep rose.
 Fluorescent Antibody Stain - extremely specific method
of detecting fungi in tissues or fluids.
 Papanicolaou Stain - good for initial differentiation of
dimorphic fungi. Works well on sputum smears.
 Gram Stain - generally fungi are gram positive; but
Actinomyces and Nocardia are gram variable.

Stains used: (continued)
 Acid-Fast Stain - used to differentiate the
acid-fast Nocardia from other aerobic
Actinomyces.
 Giemsa Stain - used for blood and bone
marrow specimens.
 India Ink - demonstrates the capsule of
Cryptococcus neoformans in CSF
specimens.

Fungal Culturing:
 Tubed media is used rather than plated media.
 Less chance for spore release into the environment.
 Less chance for dehydration.
 Easier storage.
 The agar in a tube is inoculated in a straight line.
Preliminary identification is based on
differential growth patterns on various media.

Fungal Culturing:
Media -
 Sabouraud's dextrose agar - classic medium, recommended for
most studies.
 Sabouraud's dextrose agar with chloramphenicol (inhibits bacterial
growth).
 Mycosel agar - a commercially produced agar containing
chloramphenicol to inhibit bacterial growth, and cycloheximide to
inhibit saprophytic fungi and some yeasts (including C.
neoformans).
 Aspergillus and Scopulariopsis are opportunistic pathogens.
Cycloheximide will prevent their growth. Bacteria-like fungi (such as
Actinomycetes) are inhibited by chloramphenicol.

Fungal Culturing:
Media -
 Brain heart infusion slant (BHI) - more enriched
than Sab-Dex. For recovery of H. capsulatum.
 Potato-dextrose agar (PDA) and Corn-meal agar -
used in slide cultures to induce spore formation,
which aids in identification.

Fungal Culturing:
Special applications agar -
 Caffeic Acid Agar - Cryptococcus neoformans will
produce melanin resulting in black colonies (must
protect media from light).
 Birdseed Agar - used to isolate Cryptococcus
neoformans from contaminated cultures.
 KT Medium & Kelley Agar - used to convert dimorphic
fungus Blastomyces dermatitidis from mycelial to yeast
form.
 Modified Converse Liquid Medium (Levine's) - used to
promote spherule production by Coccidioides immitis.

Fungal Culturing:
Fungal growth requirements -
 Temperature - room temperature (25-30 C.) for
most fungi.
 Nocardia sp. and some dimorphic organisms
grow best at 37 degrees C.
 Any fungus capable of growing at 37 C,
should be considered potentially pathogenic.

Fungal Culturing:
Fungal growth requirements -
 Atmosphere - True fungi are aerobic but there are a few
anaerobes among the bacteria-like fungi.
 Time - Some yeasts grow overnight. Saprophytes are
fast growers (several days). Generally cultures are held
at least 4 weeks.
 Paracoccidioides brasiliensis may require 4-5 weeks;
10 weeks are recommended if Histoplasma
capsulatum is suspected.
 Routine cultures should be examined every other day.

Colony Morphology (macroscopic features):
 Surface topography - some fungal colonies
may be free growing, covering the entire
surface of agar; others may grow in a
restricted manner.
 Surface texture - cottony or wooly (floccose),
granular, chalky, velvety, powdery, silky,
glabrous (smooth, creamy), or waxy.

Colony Morphology (continued):
 Pigmentation - Fungi may be colorless or
brightly colored. Color may be on fungus
itself, on its sporulating apparatus, on the
agar, or on the bottom of the colony
(reverse pigmentation).
 Mycelium -
 Vegetative mycelium - provides nutrition.
 Aerial mycelium – reproductive.

Microscopic evaluation:
 Teased Preparation - wet mount
 Slide Culture - gives undisturbed
microscopic morphology.
 Cellophane Tape Preparation.

Biochemical studies - used to ID yeast and yeast-
like organisms.
 Carbohydrate fermentation -
 Growth and utilization of a carbohydrate under
anaerobic conditions as determined by acid and gas
production.
 Specimen is inoculated beneath the broth.
Bromcresol purple is the indicator. Acid production
turns purple to yellow. Gas is detected by
appearance of bubbles trapped in the fermentation
tube. Observe every 48 hours for 14 days.

Biochemical studies - (continued)
 Carbohydrate assimilation -
 Determines ability to utilize a carbohydrate as
sole source of carbon.
 Bromcresol purple indicator turns from
purple to yellow.
 Tubes unchanged (as determined by
comparing to a blank tube) after 10 days are
negative.

Biochemical studies - (continued)
 Nitrogen assimilation -
 Utilizes 3 tubes with differing sources of
nitrogen. Bromthymol blue is the indicator
(blue to yellow is positive).

Growth on specific agars:
 Christensen's urea agar - Urea is
hydrolyzed by some yeast to form
ammonia (pH increases) which turns
media from yellow to dark pink.
 Caffeic acid medium (must protect media
from light) - Production of melanin by
Cryptococcus neoformans resulting in
black colonies.

Other tests:
 Germ tube - Candidia albicans & Candidia
stellatoidea produce germ tubes when
incubated in a protein medium.
 Demonstration of chlamydospores - Yeast
is inoculated by jabbing appropriate agar
(Cornmeal with tween 80) and observed
every 24 hours for 3 days for
chlamydospore production.

Hypersensitivity: (skin tests and serological
tests)
 Skin tests - demonstrates T-cell immunity
(cellular) to a fungus.
 Serological tests - demonstrates B-cell
immunity (humoral) to a fungus; sera
should be drawn in pairs (acute and
convalescent).

MycologyLabProceduresSummer20 importance12.ppt

More Related Content

Similar to MycologyLabProceduresSummer20 importance12.ppt

Recently uploaded

MycologyLabProceduresSummer20 importance12.ppt