Sketchy Micro

Question 1

Staphylococcus aureus

Answer 1

• golden staff - S. aureus
• Gram+
• beta-hemolytic
• catalase+
• coagulase+
• ferments manitol (turns golden)
• colonizes the nose
• Protein A - major virulence factors, binds Fc portion of IgG to prevent opsonization
• diseases:
  
  • septic arthritis
  • skin infections - erythematous abscesses
  • post-viral pneumonia with patchy infiltrate
  • osteomyelitis
  • acute onset endocarditis, esp the tricuspid valve, esp for IV drug users
  • acute onset food poisoning, esp vomiting
  • toxin-mediated syndromes: toxic shock and scalded skin syndrome
• MRSA - methicillin resistant S. aureus
  
  • resistance gained from altered PBPs
  • use vancomycin
• if not methicillin resistant - use nafcillin

Question 2

• Staphylococcus epidermidis*
• Staphyloccocus saprophyticus*

Answer 2

• both:
  
  • Gram+
  • catalase+
  • urease+
  • coagulase-
• S. epidermidis
  
  • infects prosthetic joints, catheters, and heart valves via biofilm formation
  • often contaminates blood cultures
  • part of normal skin flora
  • novobiocin sensitive
  • treat with vancomycin
• S. saprophyticus
  
  • causes UTIs in sexually active young women

Question 3

Streptococcus pyogenes

Answer 3

• Group A strep
• beta-hemolytic
• bacitracin sensitive
• virulence factors:
  
  • hyaluronic acid capsule - antiphagocytic
  • streptolysin O (can be tracked with ASO titer)
  • streptokinase
  • DNAse
• diseases:
  
  • pharyngitis
  • impetigo
  • erysipelas
  • toxin mediated:
    
    • Spe toxin –> A and C: toxic shock-like syndrome, B: necrotizing fasciitis
    • scarlet fever (strawberry tongue)
• post-strep diseases: happen 2 weeks after initial infection
  
  • rheumatic fever: following pharyngitis only
    
    • can be avoided with early treatment
    • JONES symptoms (joints, carditis, nodules, erythemtaous marginitis, Syndenham’s chorea)
    • caused by cross reactions between protein M and cardiac myosin - avoidance of phagocytosis
    • endocarditis of mitral valves
  • glomerulonephritis: following pharyngitis or impetigo
    
    • can’t be avoided with early penicillin treatment
    • cola-colored urine

Question 4

Streptococcus agalactiae

Answer 4

• Gram+
• encapsulated - antiphagocytic
• bacitracin resistant
• hippurate positive
• beta-hemolytic
• CAMP test positive (zone of inhibition when plated with S. aureus)
• diseases: neonates get it from passage through vaginal canal
  
  • meningitis
  • pneumonia
  • sepsis
• mothers are swabbed at 35 weeks for colonization
  
  • if colonized, intrapartum penicillin given to mother

Question 5

• Streptococcus pneumoniae*
• Streptococcus viridans*

Answer 5

• both alpha-hemolytic
• S. pneumoniae
  
  • encapsulated
    
    • sickle cell patients and patients with splenectomies are particular prone
  • optochin sensitive
  • lancet-shaped diplococcus
  • bile sensitive
  • IgA protease - virulence factor
  • diseases - number 1 cause for most these:
    
    • M - meningitis
    • O - otitis media
    • P - pneumonia - lower lobe, rusty sputum
    • S - sinusitis
  • treated with ceftriaxone and macrolides
  • vaccines
    
    • for adults –> production of IgM
    • for children –> production of IgG
• S. viridans
  
  • not encapsulated
  • optochin resistant
  • bile resistant
  • diseases:
    
    • dental caries
    • sticks to platelets in previously damaged heart valves (most likely mitral)
    • endocarditis in previously damaged heart valves
    • forms dextran

Question 6

Enterococcus

Answer 6

• 2 species:
  
  • E. faecium - 15%, more potent a bug
  • E. faecalis - 85%
• bile resistant
• grow in 6.5% salt
• diseases:
  
  • UTIs
  • endocarditis
  • infections of the biliary tree
• vancomycin resistant (VRE) - treat with linezolid and tigecycline