SSTI bacterial infections

Question 1

Staph Aureus characteristics

Answer 1

Gram (+), Catalase (+), Coagulase (+), facultative anaerobe

• Non-flagellated, non-motile, non-spore forming
• MOST STRAINS ARE BETA-HEMOLYTIC (complete hemolysis)
• On plates appear WHITE or GOLDEN color

Question 2

Structural virulence factors for Staph Aureus

Answer 2

• Capsule = antiphagocytic
• Slime layer/biofilm = facilitates adherence to foreign bodies
• Peptidoglycan = endotoxin like activity
• Teichoic acid = ADHESION
• PROTEIN A = INHIBITES ANTIBODY MEDIATED CLEARANCE BY BINDING TO IgG Fc DOMAIN

Question 3

Define cytoxins for Staph Aureus

Answer 3

• ALPHA (pore forming toxin) = pokes holes in cell membranes that allow staph to enter cell and causes lysis of the cells
• Alpha, beta, delta, gama etc are toxic for many cells (macrophages, platelets, erythrocytes, leukocytes)

Question 4

Define Exfoliative toxins for staph aureus

Answer 4

(ETA or ETB)

• SERINE PROTEASES that split the intraepidermal junctions (destory epithelial layer
• Mediates STAPHYLOCOCCAL SCALDED SKIN SYNDROME (SSSS)

Question 5

Define Enterotoxins for staph aureus

Answer 5

• Superantigens
• associated with food poisoning
• insensitive to heat and gastric enzymes

Question 6

Define Toxic shock syndrome toxin-1 for STAPH AUREUS

Answer 6

• superantigen associated with toxic shock syndrome

Question 7

Describe Virulence enzymes in staph aureus

Answer 7

• Coagulase = converts fibrinogen to fibrin (may wall off an protect bacteria
• Variety of enzymes can HYDROLYZE host tissue to aid in the SPREAD of S. Aureus throughout body

Question 8

Diagnosis of Staph aureus

Answer 8

• Gram stain (+), Catalase and coagulase (+)
• culture on blood agar aerobically (golden/white colonies, HEMOLYTIC)
• blood cultures (+) in ACUTE S. AUREUS ARTHRITIS, osteomyelitis and endocarditis
• TOXIN MEDIATED DISEASES WILL NOT NECESSARILY YIELD CULTURED MICROBES

Question 9

Treatment of Staph. Aureus

Answer 9

• Superficial lesion = resolves on its own
• extensive lesion = drainage and antibiotics
• penicillinase-resistant penicllin = NAFCILLIN, OXACILLIN
• MRSA = VANCOMYCIN

Question 10

MRSA

Answer 10

• S. Aureus that was resistance to penicillin acquires MecA gene via mobile genetic element
• Acquires Penicillin binding protein (PBP) that cross links peptidoglycan and that has LOW AFFINITY for methicillin and related penicillins and cephalosporins
  CLINICAL
• in community = SKIN INFECTIONS
• in medical facility = life-threatening bloodstream infection, pneumonia, and surgical site infections
• TREAT WITH VANCOMYCIN

Question 11

Define Osteomyelitis

Answer 11

• Bone pain, fever, swelling, malaise
• Almost always associated with bacterial infection disseminating to bone
• risk factors related to impaired blood flow to bone or exposure of bone.
• STAPH. AUREUS IS MOST LIKELY CAUSE, but can be lots of things.