Diagnostic Bacteriology

Question 1

Gram negative vs gram positive features?

Answer 1

Pink stain (2 outer membranes with thin peptidoglycan)

vs

Purple stain (1 outer membrane with thick peptidoglycan)

Question 2

4 stages of gram stain?

Answer 2

Crystal violet

Iodine

Alcohol wash

Safranin

Question 3

Coccus vs bacillus?

Answer 3

Spheres vs round ended cylinders

Question 4

Hemolytic activity?

Answer 4

Used to differentiate Staphlyococcus, Streptococcus and Enterococcus (gram positive)

Question 5

Lactose fermentation test?

Answer 5

Growth on MacConkey agar plate to differentiate between gram negative bacteria

Non-fermenting bacteria will be colourless, fermenting bacteria will be red due to acid produced

Question 6

Catalase test?

Answer 6

Determines if bacteria produces catalase, which breaks down hydrogen peroxide into O2 and H2O. Differentiates staphylococci (produce catalase) and streptococci (do not produce catalase)

Catalase + equals bubbles

Question 7

Coagulase test?

Answer 7

To see if bacteria forms coagulase, which forms clots. Used for differentiating staphylococci, in particular S, aureus (produces coagulases) and other staphylococci

Coagulase + = clumps