PBL #1 Flashcards
What are the most common organisms that cause endocarditis?
-
Staph Aureus
- Most common cause
- majority of endocarditis in IV drug users
- ACUTE
-
Strep viridans
- 2nd major cause
- SUBACUTE
-
Enterococcus
- 3rd major cause
- SUBACUTE
-
Strep Pyogenes
- ACUTE
- Staph Epidermidis
What are the pathogenic mechanisms of Staph aureus in causing endocarditis?
- most common infectious agent of the skin
- common in surgical wounds
- Virulence factors:
- biofilm formation
- capsule
- adhesins (FnbpA)
- Leukocidins
- coagulase +
- Protein A (binds Fc portion of IgG)
- hemolysins (beta-hemolysis)
- pathogenicity islands (methicillin resistance)
What are the pathogenic mechanisms of Strep viridans in causing endocarditis?
- Usually involves underlying mitral valve damage (rheumatic fever, etc.) which provides the site for bacterial colonization
- Alpha-hemolysis
- Makes Dextran for Glycocalyx formation and surface adhesion proteins (FimA, GspB) for colonization
What are the pathogenic mechanisms of Strep pyogenes in causing endocarditis?
- M protein keeps bacteria from being phagocytosed and the complement-activation cascade from being activated.
- Type II Hypersensitivity produces autoantibodies that damage heart muscle and valves → Rheumatic Heart Disease
- Attachement proteins (MSCRAMMs)
- Capsule formation
- Beta-hemolytic
What are the pathogenic mechanisms of Enterococcus species in causing endocarditis?
- Most frequently found following:
- genitourinary procedures in older men
- OB procedures in younger women
- Virulence factors:
- biofilm formation
- pili
- surface proteins
- proteases
- hyaluronidases
- resistant to penicillin and carbepenems
What is the pathophysiology and relationship between bacterial endocarditis and heart murmurs?
- Colonization on the mitral valve → Mitral valve regurgitation → Turbulent flow → causes murmur
- Holosystolic Murmur = one that continues throughout systole because blood is leaking through a structure that should normally be shut
What methods help distinguish between the various types of streptococci?
- Bacteria → Gram + → Cocci → Catalase - → Alpha-hemolytic → bacitracin resistant → S. mutans
- Bacteria → Gram + → Cocci → Catalase - → Beta-hemolytic → Bacitracin sensitive → S. pyogenes
- Alpha hemolysis - Viridans, partial degradation of red blood cells, leads to color change/oxidation and turns surrounding area green
- Beta hemolysis - Group A strep (streptococus pyogenes), will completely destroy red blood cells
What is the relationship between endocarditis and stroke?
- Vegetation (clumps of bacteria + mesh of fibrin) can break off from the valve and travel to other parts of the body, blocking blood flow.
- The risk of embolization is highest during the first week of therapy, and in patients with mobile vegetations or vegetations >10 mm in diameter occurring on the mitral valve.
- Endocarditis can also lead to hemorrhaging in the brain and other parts of the body via septic erosion of arterial walls.
- Overall, the stroke risk in patients with endocarditis is 9.1% in the first 12 months
What is the MOA of thrombolytic agents tissue plasminogen activator and streptokinase?
- tPA = converts plasminogen to plasmin
- plasmin degrades fibrin clots
- Streptokinase = biosynthetic form of tPA
What are the potential benefits and risks of of thrombolytic agents tissue plasminogen activator and streptokinase?
- Benefits:
- effective thrombolysis
- increase functional independence following CVA without affecting mortality at 3-6 months if given within 3 hours
- Risks:
- intracranial hemorrhage within the first 7 days after administration
What is the MOA of Ceftriaxone?
Binds to penicillin binding proteins and inhibits peptidoglycan synthesis.
Broad spectrum for Gram positive and negative organisms.
What is the MOA of Vancomycin?
Forms H-bonds with D-ala-D-alanine and prevents the incorporation of NAM/NAG-peptide subunits into peptidoglycan matrix.
Broad spectrum for Gram positive and negative organisms.
What is the MOA of Penicillin G?
Beta- lactam ring binds to DD-transpeptidase inhibiting cross-linking for remodeling of peptidoglycan.
Inhibits transpeptidase.
Narrow spectrum of Gram positive, aerobic organisms.
What are the physical exam findings associated with emboli?
- Vascular Phenomena:
- Splinter Hemorrhages (fingernails)
- Janeway lesions (non-tender, palms & soles)
- Petechiae
- PE
- Stroke
- Immunological Phenomena:
- Roth’s spots (retinal hemorrhages w/ pale centers)
- Osler’s nodes (tender, pads of fingers/toes)
What evidence supports a genetic risk for development of rheumatic fever?
- Monozygotic and dizygotic twins studies.
- higher prevalence in monozygotic twins
- Know what the term penetrance means.
- The percentage of individuals with a given genotype who exhibit the phenotype associated with that genotype.
