Lab 3 - Catalase Positive, Gram Positive Cocci

Front 1

What is the purpose and principle behind CNA media? What are the inhibitory agents?

Back 1

CNA is a selective medium for Gram positive bacteria, and is therefore inhibitory to Gram negative bacteria.

-Inhibitory agents: Colistin and Nalidixic acid

Front 2

What is the purpose and principle behind PEA media? What are the inhibitory agents?

Back 2

-PEA is a selective medium, similar to CNA except with a better smell. It's selective for Gram positive organisms. Phenyl ethyl alcohol is the inhibitory agent.

Front 3

What is the purpose and principle behind SBA? What are the inhibitory agents?

Back 3

-Enriched medium in which most organisms grow well on. It is enriched with 5% Sheep blood, and can also demonstrate hemolysins produced by the organism, if present. (S. aureus showed beta-hemolysis, others showed none.)

Front 4

What is the purpose and principle behind TSA? What are the inhibitory agents (if any)?

Back 4

-Supportive medium that is known for visualization of pigment production and culture maintenance. Grows many non-fastidious organisms.

Front 5

-What is the purpose and principle behind MSA?

What are the inhibitory agents?

Back 5

-Selective and differential medium. Selective because it inhibits the growth of Gram-negative bacteria due to the fact that it contains 7.5% NaCl. Differential because it contains mannitol and phenol red. If an organism is capable of fermenting mannitol, it produces acids which change (lower) pH, and the media around the colony goes from pink to yellow. S. aureus is the only organism that had a positive mannitol reaction.

Front 6

Describe the gram stain reaction, morphology and arrangement of Staphylococcus aureus?

Back 6

Gram-positive cocci in clusters

Front 7

Describe the gram stain reaction, morphology and arrangemet of S. epidermidis?

Back 7

Gram- positive cocci in clusters

Front 8

Describe the gram stain reaction, morphology and arrangement of S. saprophyticus?

Back 8

Gram positive cocci in chains

Front 9

Describe the gram stain reaction, morphology and arrangement of Micrococcus luteus.

Back 9

Gram positive cocci in clusters

Front 10

What is the catalase reaction of this week's organisms?

Back 10

S. aureus - positive reaction with evident bubbles

S. epidermidis - positive reaction with evident bubbles

S. saprophyticus - positive reaction with evident bubbles

M. luteus - positive reaction with evident bubbles

Front 11

How can the genera of Staphylococcus and Micrococcus be differentiated?

Back 11

Looking at colonial morphology on SBA. Staph colonies are small, white, creamy and opaque. Micrococcus colonies are small, creamy, opaque and yellow pigmented.

Front 12

Which enzymes (detected in clinical lab) most closely correlate with the pathogenicity of Staphylococcus aureus?

Back 12

Coagulase - free and bound, though an organism may not always produce both.

Beta-lactamase - hydrolyzes the amide bond - responsible for organism's ability to resist antibiotics of the beta-lactam class.

Front 13

What is the principle of a catalase test? What product is detected when the catalase test is positive?

Back 13

The catalase test is used to determine an organism's ability to produce the enzyme catalase. If positive, the catalase will break down hydrogen peroxide into water and oxygen.

Front 14

How could a strain of Staphylococcus aureus be slide coagulase negative and tube coagulase positive?

Back 14

If it doesn't have any bound coagulase. All strains produce free coagulase, but not all produce bound coagulase (clumping factor)

Front 15

How is Staphylococcus saprophyticus differentiated from other coagulase negative staph?

Back 15

It is resistant to Novobiocin while others are susceptible.

Front 16

What type of infection is Staph saprophyticus associated?

Back 16

Urinary tract infection - more common in females.