11 - Staph Flashcards
What are virulence factors are associated with staphylococcus?
What drug resistance is associated with staphylococcus?
Protein A Hemolysins Leukotoxins Enterotoxins (superantigens)-toxic sock syndrome toxin Exfoliative toxins
MRSA and VRSA
What is the gram type of staphylococcus? What does it look like microscopically? What type of metabolism does it do?
Gram + cocci, nonmotile.
Pairs, short chains, clusters.
Facultative anaerobes.
Where does the indigenous staphylococci establish residency?
Surface tissue or alimentary tract, especially in the anterior nares.
Part of normal flora, problem in trying to control the infection.
What are the major types of staphylococcus? What test can differentiate them?
S. aureus: coagulase +
S. epidermis: coagulase -
S. saprophyticus
Coagulase test - coagulase contributes to the clotting of plasma (converts fibrinogen to fibrin).
How would you differentiate staphylococcus from streptococcus?
Staphylococcus is catalase +
Streptococcus is catalase -
Catalase converts H2O2 to H2O and O2.
What virulence factor is unique to staphylococcus aureus?
Protein A
Major protein of cell wall covalently bound to PG.
With IgG molecules bound to protein A in the “wrong” orientation, the IgG disrupts opsonization and phagocytosis of bacteria.
What are the toxins produced by Staph. aureus?
Hemolysins
Leukotoxins
Enterotoxins (superantigens) - toxic shock syndrome toxin
Exfoliative toxin
What are the different types of hemolysins? What type does staph have?
alpha, beta, and gamma hemolysins.
Staph hemolysins are B-hemolytic (clear colonies).
These damage RBC membrane proteins and cause tissue damage after establishment of a focus of infection.
What is the function of leukotoxins produced by staph?
A two protein toxin, attacks PMNs and macrophages.
What are the characteristics of enterotoxins produced by Staph?
Heat stable superantigens causing diarrhea and emesis from the intoxication of preformed enterotoxin, not an infection.
Symptoms occur within 2-6 hrs; rapid recovery within 6-8 hrs.
Includes toxic shock syndrome toxin (TSST).
What is the function of enterotoxins?
Enterotoxins and toxic shock syndrome toxin binds to MHC class II and TCR independent of antigen and stimulates 20% of all T cells.
Causes massive cytokine production yielding systemic toxicity of host / suppression of the adaptive immune response.
What is the function of exfoliative toxin? What are the different forms?
ETA and ETB proteases.
Stimulate lysis of the intercellular attachment between cells of the epidermis.
Causes scalded skin syndrome.
What is the epidemiology of staphylococcus? How is it transmitted?
Normal part of human flora, carried asymptomatically at several body sites esp. the anterior nares.
Transmitted via direct contact by hands (hospital personnel); airborne is possible.
What are the types of infections that can be caused by staphylococcus?
- Folliculitis-hair follicle
- Boil-subQ tissue
- Impetigo: skin infection (staph/strep)
- Scalded skin syndrome: exfoliative toxin
- Pneumonia: compromised host (CF, flu, Abx, chemo, immunosuppressants)
- Osteomyelitis
- Athritis
Typically localized - primary site of infection is the skin.
What is a major barrier to staphylococcus infections?
The skin.
