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Intravascular Infection:

Intravascular Infection:. Microorganisms gain entry to the intravascular system throughout: 1-The cellular components of blood. 2-The structural elements of the circulatory system. Examples: - Plasmodium species, Babesia microti invades RBCs.

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Intravascular Infection:

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  1. Intravascular Infection: Microorganisms gain entry to the intravascular system throughout: 1-The cellular components of blood. 2-The structural elements of the circulatory system. Examples: -Plasmodiumspecies, Babesiamicrotiinvades RBCs. -HFVs infects the endothelial surface of cardiovascular components.

  2. Definitions: Endarteritis: intravascular infection of artery. It is associated with: 1-Congenital arterial anomaly; ductus arteriosus. 2-Diseased arterial endothelium; atherosclerotic plaques. Phlebitis: infection of the lumen of vein ; It is directly correlated with: 1-Directspread from an adjacentfocus of infection. 2-Intravascular foreignbodies (catheter) implanted in vein.

  3. N Infective Endocarditis: -Is an infection of the endocardial surface of the heart. -It is localized on the cardiac valves, the atrial or ventricularwall ,and the chordae tendineae. -Arise as a consequence of cardiac surgery or intra-cardiac instrumentation, and bacteremia.

  4. Classification of Endocarditis: 1-Infective. 2-Non-Infective. Or: 1-Acute: febrile , toxic illness lasting only days to several weeks. 2-Subacute: lower fever, anorexia, weakness, weight loss, and are symptomatic for longer than several weeks. Epidemiology: -Infective endocarditis accounts for 1 in 1000 admissions to large general hospitals. -More than 50% of cases involve people older than 50 years of age.

  5. N The common predisposing factors for endocarditis are: 1-Congenital cardiac defects: -Bicuspid aortic valves, ductus arteriosus, or ventricular septal defects. 2-Degenerative valvular diseases. 3-Acute Rheumatic fever: Streptococcal M protein Cross-reactivity with cardiac myosin. 4-Prosthetic heart valves. 5- Cardiac rhythm management device (CRMD).

  6. n Causes of Infective endocarditis: -Left sided endocarditis are most common, accounting for 95% of cases. -Right sided endocarditis accounts only for 5% of cases. Causes of endocarditis: 1-Native valve endocarditis: A-Acute : Staphylococcus aureus accounts for 60% of cases. 40% include alpha-Streptococcus and G-ve bacilli. Average mortality rate is 20%. Higher in patients over 65 years of age.

  7. N B-Subacute: -Alpha-Streptococciand non-hemolytic accounts for 60%. -40% include Enterococcus, Coagulase negative Staphylococcusspecies, fastidious Gram negative bacilli. -Among injection drug users (younger persons): -Staphylococcus aureus causes 75% of right-sided endocarditis. -Whereas a wide range of microbes cause left-sided endocarditis; 25% Staph aureus, 40%Streptococciand Enterococci, 18% fungi and Gram negative bacilli.

  8. N 2-Prosthetic valve endocarditis: Depends on the time after surgery when infection becomes symptomatic. A-Nosocomial acquired endocarditis: -50% of cases caused by Staphylococcus aureus. -Gram negative, Corynebacterium, and fungi. B-Community acquired endocarditis: -It occurs as a consequence of bacteremia. -It is acquired in the first year after valve replacement. -Staphylococcus aureus, Staphylococcus epidermidis (Beta-lactam resistance), and Streptococci.

  9. Pathogenesis and Microbial virulence factors: Microbial agents (Bacteremia) Host defense -Only a limited types of bacteria can cause endocarditis. -Microbial invasion into bloodstream (bacteremia). Thrombotic Vegetation Plasma Proteins Coagulation factors Endothelium adhesion, Bacterial Vegetation

  10. N -Microbes reach the cardiac valve. -Microbes resist complement-mediated bactericidal activity and escape phagocytosis. -Primary damage of valve endothelium; cytokines; expression of Beta1 integrin by endothelium; binding of plasma fibronectin; coagulation and formation of sterile vegetation (Platelet-fibrin aggregates); (non-bacterial thrombotic vegetation).

  11. N Non-bacterial thrombotic vegetation could be established also due to: 1- Cardiac abnormalities:Bicuspid aortic valves: Regurgitation of blood through the orifice of incompetent aortic valve from high pressure area to low pressure left atrium. Vegetation of ventricular side of mitral valve. 2-Malignancy and some chronic diseases.

  12. N -Increased microbial adhesion; -Alpha-hemolytic Strpetococcispecies produce extracellular dextran and Fim A adhesinthat bind strongly to fibronectin and thrombotic vegetation. -Enterococcilipoteichoic acid promotes similar adhesion. -Staphylococcus aureus fibrinogen binding protein initiate the microbial adherence to thrombotic vegetation. -Formation of bacterial vegetation (108 to 109 CFU/gm).

  13. N -Colonization of heart endocardium due to: 1-Endothelium tissue factors; formation of thrombin. 2-Destruction of endothelial cells by thrombocidins. -Bacterial vegetation occurs along the edges of the heart valves, on the ventricular side of mitral and aortic valve and on the atrial side of tricuspid valve.

  14. N Microscopically, Bacterial vegetation is a mass of platelets, fibrin, Micro-coloniesof microbes, and inflammatory cells.  In the subacute form of infective endocarditis, the vegetation also include: a center of granulomatous tissue, which may undergo fibrosis(collagen) or calcification.

  15. N -In25-35% of cases, Infective endocarditis is associated with fragmentation of vegetation into the circulation, causing peripheral septic emboli. -Visceral organs and brain involvement. -Continuous bacteremia. -Formation of antibodies complexes; serum sickness disease (focal embolic glomerulonephritis).

  16. Diagnosis of infective Endocarditis: Direct : Microbiology: 1-Blood culture results have a 95% sensitivity. 2-Surgically removed vegetation analysis by culture and PCR. Indirect: Serology: -Serologic testing have led to identification of : Rickettsia species, Coxiella species, and Bartonella as infrequent but important causes of subacute endocarditis.

  17. Non-infective Endocarditis: This form occurs more often in patients with Lupus erythematosus and is thought to be due to the deposition of immune complexes. These immune complexes form small sterile vegetation.

  18. Bacteremia: Bacteremia is the invasion of bloodstream by bacteria. The blood is normally a sterile environment, so the detection of bacteria in the blood is always abnormal. Bacteria can enter the bloodstream as a severe complication of mucosal surfaces colonization or surgical procedures: 1-Dental extraction. 2-Gingival surgery. 3-Air way infection. 4-GIT, UTI (endoscopy, catheter)

  19. Septicemia: Septicemia (sepsis) : is the invasion of bloodstream by virulent microbe and its toxins which results in acute systemic illness (SIRS and culture-documented infection). Septic shock: is a medical emergency caused by decreased blood flow and oxygen delivery to organs and tissues as a result of inflammatory response against blood sepsis. It can cause Multiple organ dysfunction syndrome and death.

  20. Bacteremia, Septicemia, and SIRS: N

  21. N -Themortality rate from septic shock is approximately 25%- 50%. Microbial virulence and pathogenesis (Sepsis and septic shock): -The Gram negative lipopolysaccharidebind to LPS-binding proteinwhich crosslink CD14in blood. -Blood monocyte, and neutrophilsdiscriminate the complexes by CD14receptors. -Lipopolysaccharide is a polyclonal B lymphocyte activator.

  22. N -Production of cytokines in bloodstream; (IL-1, IL-8, IL-12, TNF). -Systemic Vasodilation of capillary endothelium, and Vasoconstriction in the vasculature; edema and chemotaxis. -Decreased blood pressure(Hypotension), increased smooth muscle contraction of respiratory tract,hypoperfusion. -Clinical presentation of SIRS: Rapid breathing (Resp. Rate>20/min),fever >38, Heart rate > 90 beats/min, WBCs > 12000 cells/ µl.

  23. Microbial virulence and pathogenesis: Septic shock: N

  24. Sources of Bacteremia: In the hospital, indwelling catheters are a frequent cause of bacteremia, because they provide a means by which bacteria normally found on the skin can enter the bloodstream. Other sources of bacteremia include: Dental procedures ,Urinary tract infection,Respiratory tract infection, GIT infection, intravenous drug use, Contaminated endoscopy or colonoscopy, Post-operative infection.

  25. Causes of Bacteremia and Sepsis: 1-Gastrointestinal infection: Typhoid fever (Salmonellosis), Malta fever (Brucellosis), Yersinia infection and Bacteroidfragilis. 2-Genitourinary tract infection: Staphylococcus aureus, E.coli, Klebsiella, Citrobacter, Enterobacter, and Pseudomonus species. Treponema pallidum.

  26. N 3-Respiratory tract infection: Neisseria meningitidis, H. influenza, Streptococcus pneumoniae, MRSA, VRE, and Klebsella pneumonia. 4-Skin infections. Diagnosis of endocarditis and Bacteremia: Blood culture: A- a5-8 ml blood should be extracted for culture. B- Specimens should be extracted during fever stage. C- Inoculation of blood culture bottle, and incubation under aerobicand anaerobicconditions at 37C for up to 8 days.

  27. Blood culture procedure: N

  28. Blood culture growth indicators: 1-Turbidity of blood culture media. 2-Air bubbles formation in the media. 3-Hemolysis of cultivated blood.

  29. Identification of pyogenic Cocci isolated from Blood culture: n

  30. Staphylococcus species: DNasepostive Staphylococcus aureus Coagulase positive

  31. N Streptococcusviridansspecies are resistant to Optichin and insoluble in bile salt.

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