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.
-HFVs infects the endothelial surface of cardiovascular components.
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-Direct spread from an adjacent focus of infection. 2-Intravascular foreign bodies (catheter) implanted in vein.
Infective Endocarditis: -Is an infection of the endocardial surface of the heart.-It is localized on the cardiac valves, the atrial or ventricular wall ,and the chordae tendineae.-Arise as a consequence of cardiac surgery or intra-cardiac instrumentation, and bacteremia.
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.
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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).
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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.
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B-Subacute: -Alpha-Streptococci and non-hemolytic accounts for 60%. -40% include Enterococcus, Coagulase negative Staphylococcus species, 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% Streptococci and Enterococci, 18% fungi and Gram negative bacilli.
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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.
Pathogenesis and Microbial virulence factors:-Only a limited types of bacteria can cause endocarditis.-Microbial invasion into bloodstream (bacteremia).
Microbial agents(Bacteremia)
Plasma ProteinsCoagulation factors
Thrombotic VegetationHost defense
Endothelium adhesion, Bacterial
Vegetation
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-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).
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-Increased microbial adhesion;
-Alpha-hemolytic Strpetococci species produce
extracellular dextran and Fim A adhesin that bind
strongly to fibronectin and thrombotic vegetation.
-Enterococci lipoteichoic 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).
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-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.
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Microscopically, Bacterial vegetation is a mass
of platelets, fibrin, Micro-colonies of 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.
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-In 25-35% 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).
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.
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.
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)
Septicemia:
Septicemia (sepsis) : is the invasion of bloodstream by
virulent microbe and its toxins which results in acute
systemic illness.
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.
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-The mortality rate from septic shock is approximately 25%- 50%.
Microbial virulence and pathogenesis(Sepsis and septic shock):
-The Gram negative lipopolysaccharide bind to LPS-binding
protein which crosslink CD14 in blood.
-Blood monocyte, and neutrophils discriminate the
complexes by CD14 receptors.
-Lipopolysaccharide is a polyclonal B lymphocyte activator.
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-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, increased smooth muscle
contraction of respiratory tract.
-Rapid breathing, low blood pressure, fever, and lethal
shock.
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.
Causes of Bacteremia and Sepsis:
1-Gastrointestinal infection:
Typhoid fever (Salmonellosis), Malta fever (Brucellosis),
Yersinia infection and Bacteroid fragilis.
2-Genitourinary tract infection:
Staphylococcus aureus, E.coli, Klebsiella, Citrobacter,
Enterobacter, and Pseudomonus species.
Treponema pallidum, and Neisseria gonorrheae.
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3-Respiratory tract infection:
Neisseria meningitidis, H. influenza, Streptococcus
pneumoniae, MRSA, VRE, and Klebsella pneumonia.
Diagnosis of endocarditis and Bacteremia:Blood culture:A- a 5-8 ml blood should be extracted for culture.B- Specimens should be extracted during fever stage.C- Inoculation of blood culture bottle, and incubation under aerobic and anaerobic conditions at 37C for up to 8 days.
Blood culture procedure:N
Blood culture growth indicators:
1-Turbidity of blood culture media.2-Air bubbles formation in the media.3-Hemolysis of cultivated blood.
Identification of pyogenic Cocci isolated from Blood culture:n
Staphylococcus species:
DNase postive Staphylococcus aureus Coagulase positive
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Streptococcus viridans species are resistant to Optichin and insoluble in bile salt.