Staphylococci

Question 1

Staphylococcus Aureus

Answer 1

gram positive
coagulase positive
forms clusters not chains

Question 2

Staphylococcus Aureus virulence factors

Answer 2

• biofilm
• surface factors–proteins that facilitate binding
• secreted proteins–for hemolysis and spreading of infection

Question 3

Protein A

Answer 3

• a virulence factor on staphylococcus aureus
• found in the cell wall
• binds to Fc part of IgG preventing complement fixation and phagocytosis
• enhances ability to cause inflammatory diseases-skin, endocarditis, pneumonia

Question 4

Polysaccharide capsule

Answer 4

found on staphylococcus aureus

prevents opsonization for phagocytosis

Question 5

Staphylococcus (general) Pathogenesis

Answer 5

• usually pyogenic (pus forming)
• infection results in the production of toxins and chemotactic substances
• coagulase positive strains are more virulent that coagulase negative strains
  positve: staph aureus
  negative: staph epidermis

Question 6

Toxin Mediated Mechanisms

Answer 6

Organism releases a toxin that then causes issues

• TSS (TSST 1)
• rapid onset food poisoning (enterotoxin)
• scalded skin syndrome (exofoliative toxin)

Question 7

Bacterial adherence & dispersion

Answer 7

• Bacteria adhere to surfaces and aggregate

- Bacteria can then disperse and travel through the system

Question 8

Host Immune Response

Answer 8

• Primarily mechanical (skin)
• Neutrophil phagocytosis
• Opsonization

Question 9

Staph Aureus: clinical syndromes

Answer 9

• skin and soft tissue infections
• vascular infections (endocarditis)
• metastatic infections
• osteomyelitis
• hospital-acquired infections
• TSS
• food poisoning

Question 10

Skin & Soft Tissue Infections

Answer 10

Abscess, impetigo, cellulitis, chalazion

Question 11

Vascular Infections

Answer 11

Endocarditis (vegetations on aortic valve), endocarditis & microemobli, metastatic infection, osteomyelitis & septic arthritis

Question 12

Hospital-Acquired Infections

Answer 12

Operations/devices, catheters, staphylococcal pneumonia

Question 13

Staphylococcal Food Poisoning

Answer 13

No invasion by organism

• usually due to poorly refridgerated dairy
• rapid onset and resolution

Question 14

Methicillin-Resistant Staphylococcus Aureus (MRSA)

Answer 14

Community or hospital acquired pathogen that attacks soft tissues

• Treat via: penicillins & vancomycin (cell wall attackers)
• community acquired is usually more antibiotic sensitive than hospital acquired
• Oral or IV treatment dictated by site/type of infection

Question 15

Staphylococcus Epidermidis

Answer 15

• Coagulase negative, not as virulent as staph aureus
• normal inhabitant of the skin
• can invade body during surgery due to foreign body/devices
• key clinical syndromes: intravascular devices causing infection, infections associated with CNS & foreign bodies

Question 16

Staph epidermidis: pathogenic concepts

Answer 16

Biofilms: colonize catheters/polymer surfaces by forming a thick polysaccharide slime layer

• this layer contains embedded organisms
• allows organism to persist despite antibiotics and host immune response

Question 17

Staphylococcus saprophyticus

Answer 17

UTI

-due to specific receptors that let it bind to genitourinary tract