Role of microscopy in ID diagnosis

Question 1

Describe how to prepare a specimen and perform a gram stain.

Answer 1

1. place cells on slide
2. primary stain crystal violet
3. mordant grams iodine
4. washout with alcohol or acetone
5. counterstain safranin

gram positive will stay purple
gram negative will be pink from safranin

Question 2

Explain the clinical utility of a gram stain.

Answer 2

• direct examination for diagnosis
• determine quality of specimen
• provide early presumptive identification
• clinical relevance of culture

Question 3

Describe the best specimens to collect for direct examination.

Answer 3

• pneumococci
• gonococci
• neisseria meningitidis
• cryptococcus
• candida

Question 4

List organisms that stain positive in acid-fast stains.

Answer 4

def: stains bacteria with cell walls containing LCFAs
method: use heat to drive stain into cell to avoid decolorization
positive organisms
- mycobacteria
- nocardia
- cryptosporidia
- cyclospora

Question 5

List the 4 types of fungal stains and the organisms identified with each type.

Answer 5

1. lactophenol cotton blue
   - histoplasma
2. gomori methenamine silver (GMS)
   - yeast cells and hyphae
   - pneumocystis carinii
   - aspergillis
   - blastomyces dermatitidis
3. periodic acid-schiff (PAS)
   - yeast cells and hyphae
   - aspergillis
   - blastomyces dermatitidis
4. mucicarmine (mucin)
   - cryptococcus capsule

Question 6

List the 4 types of parasitology stains and the organisms identified with each type.

Answer 6

1. Wright’s Giemsa
   - used on peripheral blood smear
   - histoplasma, leishmania, trypanosomas, malaria
2. Wet Mounts
   - giardia
3. Trichrome
   - giardia
4. modified acid fast

Question 7

Identify the following bacteria from a gram stain image

• staphylococcus aureus
• neisseria meningitides
• streptococcus pneumoniae
• E. coli
• actinomyces species
• campylobacter species
• nocardia species

Answer 7

see kate’s ppt in notes

see micro bugs slide link in objectives handout