Download 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.
-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.
N
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.
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).
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.
N
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.
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.
Pathogenesis and Microbial virulence factors:
-Only a limited types of bacteria can cause endocarditis.
-Microbial invasion into bloodstream (bacteremia).
Microbial agents
(Bacteremia)
Host defense
Thrombotic
Vegetation
Endothelium
adhesion, Bacterial
Vegetation
Plasma Proteins
Coagulation factors
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).
N
-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).
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.
N
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.
N
-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.
N
-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.
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, 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.
N
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
N
Streptococcus viridans species are resistant to Optichin
and insoluble in bile salt.