Microscopy in ID

Question 1

Gram Stain

Answer 1

Based on composition of cell walls (gram+ is purple, gram- is pink)

Cells on slide -> crystal violet stain -> iodine mordant -> decolorizer (alcohol and/or acetone) -> counterstain safranin

The decolorization step removes the lipid bylayer, since gram+ don’t have LPS nothing happens (purple dye remains)

Question 2

Clinical Utility of Gram stain

Answer 2

Direct examination of clinical material for initial diagnosis

Determine quality of the specimen

Suggest unusual organism or early presumptive bacterial identification

Very clinical relevance of the culture

Question 3

Acid Fast stain

Answer 3

Mycobacteria

Nocardia

Cryptosporidia

Cyclospora

TB

Question 4

Fungal stains

Answer 4

Lactophenol cotton blue: Histoplasma

Gomori methenamine silver aka GMS: yeast, pneumocystis carinii,

Periodic acid-Schiff aka PAS: yeast

Mucicarmine aka mucin: Cryptococcus capsule

Question 5

Parasite stains

Answer 5

Wright’s giemsa: histoplasma, leishmania, typanosomas, malaria

Wet mounts: giardia

Trichrome: giardia

Modified acid fast:

Question 6

Answer 6

Gram stain

Staphylococcus aureus

Question 7

Answer 7

Gram stain

Streptococcus pneumoniae in sputum

Question 8

Answer 8

Gram stain

Neisseria meningitidis in CSF

Question 9

Answer 9

Gram stain

E. coli in blood culture

Question 10

Answer 10

Gram stain

Actinomyces

Question 11

Answer 11

Gram stain

Campylobacter jejuni

Question 12

Answer 12

Gram stain

Nocardia