Microbio Lab Quiz 9

Gram Positive Cocci

What is enriched media? Give examples.

Allows many types of bacteria to grow, even fastidious bacteria 

Ex. Blood Agar, Chocolate Agar 

What is differential media? Give examples.

Allow you to distinguish one group of bacteria from another after they have grown on the media

Ex. Mannitol Salt Sugar, Blood Agar

What is selective media? Give examples.

Allow some types of bacteria to grow and not others

Ex. Mannitol Salt Agar 

What kind of bacteria only grow on blood agar?

Fastidious 

Describe the characteristics of Staphylococci 

• Gram-positive spheres growing in irregular clusters

• Catalase-positive

• Salt-tolerant 

Where are Staphylococci normally found on our bodies?

On our skin and on our mucus membranes

Where is S. epidermis normally found? Does it cause any diseases? If so, what?

In the skin and mucous membranes, it doesn’t normally cause any diseases

Where is S. saprophyticus normally found? Does it cause any diseases? If so, what?

It is found only infrequently on our bodies.

It is associated with urinary tract infections in women from ages 16-25

Where is S.aureus normally found? Does it cause any diseases? If so, what?

It is found on the skin, internal nares, vagina. 

Is causes TSS (toxic shock syndrome), food poisoning, scalded skin syndrome, pneumonia, meningitis, sinusitis, otitis media, abscesses 

What do each of the following toxins or enzymes do?

• Hemolysins

• Coagulase

• Gelatinase

• Leucocidin

• Hyaluronidase

• Staphylokinase

• Enterotoxin

Hemolysins

Destroy red blood cells 

Coagulase

Coagulate plasma

Gelatinase 

Liquefy gelatin 

Leucocidin 

Destroys white blood cells 

Hyaluronidase

Destroys connective tissue (“spreading factor”)

Staphylokinase

Dissolves fibrin clots 

Enterotoxin

Affects the digestive system (produced in food, not the body)

What Staph species produces the substances listed above?

Staphylococcus Aureus

What does Mannitol Salt Agar (MSA) select for? What ingredient is present in MSA that causes it to be selective?

MSA selects for salt-tolerant bacteria (like staph)

9.5% Salt

How is MSA differential? What does it differentiate between? What ingredients are present in MSA that cause it to be differential?

It distinguishes mannitol fermenters from mannitol nonfermenters

MSA contains mannitol and an acid-base indicator 

Why are “hospital” strains of Staph a particular problem?

They have a better chance at being antibiotic resistant 

List several members of the normal flora of the respiratory system?

• Strep

• Staph

• Neisseria

• Propionibacterium

• Lactobacillus 

Which parts of the respiratory system normally have microbes present?

• Upper Respiratory Tract

• The Nasal Membrane and the Throat (most abundant)

• A few in the Sinuses 

What defenses help protect the respiratory system from microbial invasion?

Mucus secretions and ciliated epithelium of the upper respiratory tract membranes 

Describe the members of the genus Streptococcus

Gram-positive spheres arranged in chains, catalase negative 

What does fastidious mean?

These bacteria need enriched medium to grow on

What type of media do strep need to grow on?

Enriched (blood agar plates)

One way strep are classified is by the type of hemolysis they produce on blood agar. Describe the following:

• Alpha Hemolytic Strep

• Beta Hemolytic Strep

• Gamma Strep

Alpha Hemolytic Strep

BAP turns red to green because they incompletely break down hemoglobin

Beta Hemolytic Strep

BAP clears to colorless because they completely break down hemoglobin

Gamma Strep

No change

What groups do normal flora belong to?

Alpha and Gamma

Do any of the normal flora cause disease? How?

Yes, as opportunists

Which group of strep causes disease? List examples.

Beta Hemolytic (Streptococcus Pyogenes)

Toxic shock syndrome, strep throat, scarlet fever, rheumatic fever

A second way strep can be classified is by the type of carbohydrate antigens present in their cell wall. What is an antigen?

Any substance that causes antibodies to be produced by the body, it only reacts with its specific antibody

How are these strep named?

Group A, Group B…Group T 

Human pathogens belong to which group?

Group A

Colony Color on Blood Agar

• S. Aureus → Yellow

• S. Epidermis → White

• S. Saprophyticus → White or Yellow

Type of Hemolysis of Blood Agar

• S. Aureus → Beta

• S. Epidermis → Gamma

• S. Saprophyticus → Usually Gamma

Coagulase (+ or -)

• S. Aureus → +

• S. Epidermis → -

• S. Saprophyticus → -

Mannitol Fermentation

• S. Aureus → +

• S. Epidermis → -

• S. Saprophyticus → Varies +/-

Novobiocin (S or R)

• S. Aureus → S

• S. Epidermis → S

• S. Saprophyticus → R