Micro

Question 1

Gram stain

+-

Order of steps

Answer 1

Crystal violet
Grams iodine
Alcohol
Safranin

Gram positive are purple
Gram negative are pink

Question 2

Acid fast stain

Answer 2

Mycobacterium have mycolic acid in cell walls, gram stain won’t work

Rods stain pink/red

Question 3

Catalase test

Answer 3

Will be positive for bacteria that produce catalase enzyme

Catalase degrades hydrogen peroxide

Use this to differentiate staphylococci (+) from streptococci (-)

Question 4

Coagulase test

Answer 4

Test for production of coagulase

Coagulase causes blood plasma to clot by converting fibrinogen to fibrin

Use to differentiate staphylococcus aureus (+) from other staphylococci

Positive test means you can’t get rid of granular clumps

Question 5

Oxidase test

Answer 5

Test for production of cytochrome oxidase enzyme

Cytochrome oxidase oxidizes an artificial electron donor to a colored product

Use to differentiate specific gram negative bacteria:

Neisseria and Moraxella catarrhalis are positive

Most pseudomonas are positive

Aeromonas is positive

Question 6

Hemolysis

Answer 6

Alpha hemolysis: partial lysis of red blood cells results in greenish area

Beta hemolysis: complete lysis of rbcs produces clear zone

Gamma hemolysis: no hemolysis, no change to agar

Question 7

P disk

Answer 7

Optochin sensitivity

Differentiates streptococcus pneumoniae (sensitive) from other a-hemolytic streptococci

Resistant: no zone of inhibition

Question 8

A disk

Answer 8

Bacitracin sensitivity

Differentiate lancefield group a streptococci from other B-hemolytic non group A streptococci

If zone of inhibition observed, then group A

Question 9

Bile esculin

Answer 9

Use to distinguish enterococcus faecalis (positive) from other non-hemolytic cocci

Blackening of media=positive test

Hydrolyze glycoside esculin in presence of bile