Diagnostic Bacteriology

Question 1

Gram staining

Answer 1

Gram negative have 2 outer membranes and thin peptidoglycan which stains PINK
gram positive has one outer membrane and thick peptidoglycan which stains purple

Question 2

Spheres vs cylinders

Answer 2

Spheres means coccus
Cylinders means bacillus

Question 3

Haemolytic activity

Answer 3

Gamma hemolysis means no hemolysis
Alpha hemolysis means partial hemolysis
Beta hemolysis means complete hemolysis

Question 4

Lactose fermentation

Answer 4

No growth means bile salt has inhibited growth
Lactose fermentating bacteria produce acid turning plate pink
Lactose non fermenting turn yellow

Question 5

Catalase test

Answer 5

Discriminates staphylococci which produces catalase with streptococci which doesn’t produce catalase
Catalase + produces oxygen bubbles
Catalase- produces no bubbles

Question 6

Coagulate test

Answer 6

Coagulase is an enzyme that cross links fibrinogen in plasma to form a clot
Differentiates between s.aereus which makes coagulase and staphylococci which doesn’t
Coagulase + means clumps