Lab Exercise 14: Biochemical Differentiation of some Medically Important Gram Positive

Cocci

Beta ( β ) hemolysis (blood agar around bacterial colonies is completely clear, indicating complete breakdown and

consumption of hemoglobin)

Alpha (α) hemolysis (blood agar around bacterial colonies looks greenish-brown, indicating partial breakdown and consumption of hemoglobin)

Mixed culture from a throat swab; note several β-hemolytic colonies

Gamma (γ) hemolysis (really means no hemolysis; blood agar around colonies looks normal)

Side-by-side comparisons of alpha (α), beta (β), and gamma (γ) hemolysis

Bacitracin (Taxo A) sensitivity

+ results with a zone of inhibition

A

- Result with no zone of inhibition

Optochin (Taxo P) sensitivity

- Results with no zone of inhibition + results with a zone of inhibition

PP

Coagulase Test

+

-

Carbohydrate Fermentation Tests (Glucose and Mannitol)

+ - (same as uninoculated media)

Phenol red indicator turns yellow at acid pH

Catalase Test

- +

Staphylococcus epidermidis

Enterococcus faecalis

G M

Who am I?

Use the chart on p. 146 and/or the flow chart on p. 147 of your lab manual to figure out who I am!

Answer: Streptococcus pyogenes

G M

Use the chart on p. 146 and/or the flow chart on p. 147 of your lab manual to figure out who I am!

Answer: Micrococcus lutea

G M

Use the chart on p. 146 and/or the flow chart on p. 147 of your lab manual to figure out who I am!

A

Answer: Enterococcus faecalis

G M

Use the chart on p. 146 and or the flow chart on p. 147 of your lab manual to figure out who I am!

Answer: Staphylococcus aureus

M G

Use the chart on p. 146 and/or the flow chart on p. 147 of your lab manual to figure out who I am!

Answer: Staphylococcus epidermidis

M G

Use the chart on p. 146 and or the flow chart on p. 147 of your lab manual to figure out who I am!

Answer: Streptococcus pneumoniae

G M

Use the chart on p. 146 and/or the flow chart on p. 147 of your lab manual to figure out who I am!

A

Answer: Streptococcus mutans