Anatomy/Heart
Where are vegetations most commonly located and why?
Most commonly on the mitral valve, followed by the aortic valve. This is because vegetations form at sites of highest turbulence and mechanical stress — like the atrial surface of the mitral valve (the side facing the low-pressure jet of regurgitant flow) and the ventricular surface of the aortic valve.
How is Viridans Streptococci transmitted?
bacteria is acquired from the patient's own endogenous oral flora via routine oral activities (brushing, flossing), dental procedures that involve gingival tissues, oral disease and poor dental hygiene.
the magnitude of bacteremia depends on tissue trauma and local inflammation.
Why do we obtain a culture sample of 3 sites when checking for IE? Why do we want to obtain our culture before starting antibiotics?
We take a culture sample BEFORE because antibiotics can kill or suppress bacteria in the blood-stream, giving us a false negative.
What are the contraindications for vancomycin and ceftriaxone?
vancomycin: hypersensitivity, corn allergy, those with renal impairment, people who are pregnant or breastfeeding, do not administer via these routes: intramuscular, intrathecal, intraventricular, intraperitoneal, intracameral, or intravitreal.
ceftriaxone: hypersensitivity, those allergic to beta lactams, premature neonates, those with severe renal and hepatic impairment, pregnant or lactating women,
What are the cardiac findings in a person with infective endocarditis?
When doing an echocardiogram, we see:
- mobile valvular vegetationGenerally: presence of a new murmur or change of an existing murmur.
What drugs are the viridans group streptococci susceptible and resistant to?
Commonly susceptible to vancomycin and advanced beta-lactams like ceftriaxone.
Show increasing resistance to penicillin (up to 40% of strains), macrolides (25-50%), tetracyclines, and TMP-SMX (can exceed 75%).
Citation: Singh N, Poggensee L, Huang Y, Evans CT, Suda KJ, Bulman ZP. Antibiotic susceptibility patterns of viridans group streptococci isolates in the United States from 2010 to 2020. JAC Antimicrob Resist. 2022 May 19;4(3):dlac049. doi: 10.1093/jacamr/dlac049. PMID: 35599725; PMCID: PMC9117386.
Describe the purpose and process of antibiotic susceptibility studies.
purpose: determine whether an isolated bacterium is susceptible, intermediate, or resistant to specific antibiotics. Results can be used to narrow empiric therapy, change to a more active antibiotic, or discontinue agents that are unnecessary or ineffective.
collect specimen → culture and identify organism → perform susceptibility testing via kirby bauer or MIC testing → interpret MIC or inhibition zone → report results.
What is the spectrum of ceftriaxone?
Works against gram positive and gram negative aerobes. Works against a few anaerobes. Does not cover fungi, viruses, MRSA, or C. Diff.
Describe the etiology, composition, and pathologic effects of vegetations.
What are the virulence factors of Viridans Streptococci?
Dextran: promotes binding to fibrin-platelet aggregates on cardiac valves
FimA/Lral Adhesin facilitates attachment to fibrin-platelet matrix of sterile vegetations
Biofilm Formation supports adherence to dental surfaces and can protect bacteria from host clearance
lipotechicoic Acid contributes to adherence and stimulates inflammation througjh TLR2 signaling
What is the clinical presentation of infective endocarditis?
can depend on whether it is acute IE or subacute IE. for our patient:
progression over weeks to months with fever, malaise, chills, night sweats, weight loss, dyspnea, back pain, myalgia, anthralgia
Osler's nodes, janeway lesions, splinter hemorrhages, roth spots (splinter hemorrhages), splenomegaly, acute confusional state
What is the spectrum of vancomycin?
Broad activity against gram-positive organisms, including MRSA, but no activity against gram-negative bacteria, mycobacteria, or fungi.
Compare and contrast congenital and new murmurs. How are they classified?
How murmurs are classified:
What are the features of Viridans Streptococci?
Reconcile the CBC and RF test results.
↑ WBC: Ongoing bacterial infection → inflammatory cytokines stimulate leukocyte production/release
↑ Neutrophils: Neutrophils are the major WBC response to bacterial infection
↑ Platelets: Inflammation can cause reactive thrombocytosis
↑ Rheumatoid factor: an autoantibody that targets IgG: caused by chronic infection → lots of antigen-antibody complexes and B-cell activation which can actually cause synthesis of autoantibodies.
↓ Hgb + ↓ Hct: Mild anemia related to her prolonged inflammatory illness (IL6 increases hepcidin production, this lowers circulating iron and iron absorption in order to starve bacteria, but with less circulating iron we get anemia.
What are the adverse effects of vancomycin and ceftriaxone?
Ceftriaxone: GIVEN PARENTERALLY, NOT ORALLY. adverse reactions include rash and other hypersensitivities, GI complications, hematologic effects, biliary and urinary precipitation, neurologic effects (confusion, encephalopathy).
Describe the overall structure and function of the valves and chambers of the heart. What order does blood flow?
Blood flow order:
What is the pathophysiology/order in which viridans streptococci causes infective endocarditis?
How do we formally diagnose infective endocarditis?
What are the mechanisms of action of vancomycin and ceftriaxone?
Vancomycin binds the terminal D-Ala-D-Ala sequence of bacterial peptidoglycan precursors, blocks glycopeptide polymerization and inhibits peptidoglycan cell-wall synthesis, leading to cell wall damage and death.
Ceftriaxone is a β-lactam antibiotic and is usually bactericidal. It binds penicillin-binding proteins and inhibits transpeptidase-mediated peptidoglycan cross-linking, preventing formation of a stable bacterial cell wall and leading to bacterial death.