Staphylococcus and Streptococcus

Question 1

How do staphylococcus aureus and streptococcus pyogenes identify on gram staining?

Answer 1

They are both Gram positive.

Question 2

Describe staphylococcus aureus.

Answer 2

Gram+, catalase and coagulase postivie, Non-motile, facultative anaerobe; High salt media is selective

Question 3

Name the 2 types of disease staph aureus can cause.

Answer 3

Invasive and toxigenic

Question 4

What are the types of invasive diseases Staph aureus causes?

Answer 4

Abscesses, wound infections, and pneumonia

Question 5

What are the types of toxigenic disease Staph aureus causes?

Answer 5

Scalded skin syndrome, Toxic shock and food poisoning.

Question 6

Describe the surface antigens of S. aureus.

Answer 6

1. Capsule: Polysaccharide, antiphagocytic.
2. Slime layer: Facilitates adherence to foreign objects; Protects from neutrophils
3. Protein A: Binds Fc of IgG; Prevents opsonization by antibody.
4. Peptidoglycan: Activates complement; Leukocyte chemoattractant.
5. Teichoic Acid: Binds fibronectin; Activates complement

Question 7

Describe the cytotoxins of S. aureus

Answer 7

1. Alpha-toxin: Pore forming; Chromosome or Plasmid encoded
2. Beta-toxin: Hydrolyzes membrane phospholipids
3. Delta-toxin: Acts as a surfactant.
4. PV leukocidin and Gamma toxin: Pore forming, phage encoded, damages neutrophils and macrophages, lung infections.

Question 8

Describe the exfoliating toxins.

Answer 8

Serine proteases disrupt stratu granulosum; Causes scalded skin syndrome and bullous impetigo

Question 9

Describe the superantigen toxins of S. aureus.

Answer 9

1. Toxic shock syndrome toxin: Requires oxygen and pH 7 for expression; Penetrates mucosal barriers causing systemic toxicity.
2. Enterotoxins: Heat resistant, resistant to gastric enzymes; Causes food poisoning. Organism does not have to be eaten, only the toxin.