Bacterial Culture

Question 1

Blood agar

Answer 1

1. Commonly used to differentiate species of streptococcus:
   
   • Alpha
   • Beta
   • Gamma
2. Special features of pseudomonas:
   
   • Beta-hemolytic
   • Greenish-metallic appearing colonies
   • Production of the pigments pyoverdin and pyocyanin
3. Staph Aureus
   
   • Beta hemolytic

Question 2

H influenzae

Answer 2

Chocolate agar: factors V (NAD+) and X (hematin)

Question 3

N gonorrhoeae, N meningitidis

Answer 3

Thayer-Martin agar - selectively favors growth of Neisseria by inhibiting growh of:

- gram+ organisms with vancomycin
- gram- organisms (except Neisseria) with trimethoprim and colistin
- fungi with nystatin

Question 4

B pertussis

Answer 4

Bordet-Gengou agar - potato extract

Regan-Lowe medium - charcoal, blood, and antibiotic

Question 5

C diphtheriae

Answer 5

1. Tellurite agar (cysteine-tellurite agar):
   
   • C diphtheria reduces potassium tellurite to tellurium
   • produces gray-black colored colonies
2. Löffler medium

Question 6

M tuberculosis

Answer 6

1. Löwenstein-Jensen medium:
   
   • Eggs, flour, glycerol, salt
   • M tuberculosis is slow growing (several weeks for visible colonies to appear)
   • M tuberculosis: Ziehl-Neelsen stain
2. Middlebrook medium
   Rapid automated broth (borsh, sho’rva, bulyon) cultures

Question 7

M pneumoniae

Answer 7

Eaton agar: requires cholesterol

Question 8

Lactose-fermenting enterics

Answer 8

MacConkey agar: lactose fermentation produces acid, causing colonies to turn pink; non-lactose fermenters are colorless

- selective media for gram(-) bacteria
- contains bile salts as inhibitors of growth
- inhibit gram(+) bacteria

Question 9

E coli

Answer 9

Eosin-methylene blue (EMB) agar:

- similar in function to MacConkey' agar
- eosin Y and methylene blue as inhibitors
- inhibit gram(+) bacteria
- also differential for lactose fermenters: lactose fermenters (E coli) appear as colonies with green metallic sheen or blue-black to brown color; non-lactose fermenters are colorless or transparent colonies

Question 10

Brucella, Franciella, Legionella, Pasteurella

Answer 10

Charcoal yeast extract agar buffered with cysteine and iron

Question 11

Fungi

Answer 11

Sabouraud agar (acid or antibiotics inhibit bacterial growth)