Exam #7: Bacterial Infections of the Circulatory System Flashcards
What is bacteremia?
Bacteria in the blood
*Note that this is NOT uncommon & can occur with minor things like brushing your teeth
What are the most common sources of bacteremia?
1) UTI
2) Respiratory Tract Infection
3) Soft tissue trauma
What causes transient bacteremia?
Dental extraction; this is when there is a high concentration of bacteria over a short period of time
What causes intermittent bacteremia?
- Pneumococcal pneumonia
- Gram-negative sepsis
- Intra-abdominal abscess
This is when bacteremia occurs with irregular patterns i.e. there are waves of bacteremia
What causes continuious bacteremia?
- Infective endocarditis (low level bacteremia)
- Catheter bacteremia (high level bacteremia)
What is sepsis?
Systemic inflammatory response syndrome (SIRS) that has a proven or suspected microbial etiology
*Bacteremia can lead to sepsis, but it is NOT required for sepsis
What is the definition of SIRS?
Two or more of the following:
- Fever or hypothermia
- Tachypnea
- Tachycardia
- Abnormal WBC count (i.e. leukocytosis, leukopenia, or >10% bands)
What is severe sepsis?
Sepsis PLUS one or more signs of organ dysfunction:
- Reduction in urine output
- Mental status change
- Systemic acidosis
- Hypoxemia
What is septic shock?
Severe sepsis + hypotension
What is refractory septic shock?
Septic shock that last for more than an hours & does NOT respond to fluid & pharmacologic treatment
What is multiorgan failure?
Dysfunction of >1 organ & the development of disseminated intravascular coagualtion (DIC)
*IL-6–>TNF-a–>DIC
What causes the majority of severe sepsis cases?
Bacterial infection
Is bacteremia required for sepsis?
No
What are the risk factors for sepsis?
- Indwelling catheters
- Mechanical devices
- Immunsuppression
Outline the pathophysiology of classic sepsis.
- Classically, sepsis is induced by Gram (-) bacteria that release LPS/ Lipid A into the circulation
- Binds CD14 & TLR4 that activates the immune system
- Causes inflammation & can induce septic shock via TNF-a, IL-1, & IL-6
How do Gram (+) bacteria induce sepsis?
- Peptidoglycan
- Exotoxins
How does S. aureus lead to the development of sepsis?
TSST-1= superantigen that stimulates T-cell activation & release of cytokines
- Previously most commonly seen with tampons
- Now most commonly seen with wound infection
How are staphylococcus & streptococcus differentiated in the lab?
Catalase
How does streptococcal toxic shock sydrome differ from S. aureus?
Bacteremia is present in strep.
How does Strep produce toxic shock syndrome?
- GAS (s. pyogenes) releases pyogenic exotoxins (Spe A, B & C) that are superantigens
- Stimulates T-cell activation & release of cytokines
How is sepsis diagnosed?
1) Symptoms
2) Blood cultures– 40-70% will be positive for bacteria
3) 95% of cases of infective endocarditis will yield positive cultures
*Note that in bacteremic patients without endocarditis, it is important to take multiple blood cultures over time
Will patients undergoing antibiotic therapy have positive blood cultures?
No
How is sepsis treated?
Hypotension= IV fluid Hypoxia= ventilator DIC= transfusion or heparin
*Bacterial infection= antibiotics
What antibiotics are used to treat sepsis with an unknown bacterial etiology?
Vancomycin & gentamicin
What is infective endocarditis?
Inflammation of the innermost layer of tissue that lines the chambers of the heart
What is acute endocarditis? List the characteristics of acute endocarditis. What organism typically causes acute endocarditis?
S. Aureus causes Acute endocarditis
- High fever
- Rapid damage to cardiac structures
*If left untreated, acute endocarditis can lead to death within weeks
What is subacute endocarditis? List the characteristics of subacute endocarditis. What organism typically causes subacute endocarditis?
S. viridans causes subacute endocarditis
- Low grade fever
- Night sweats
- Weight loss
- Vague constitutional symptoms
- Slower damage to the heart
*If left untreated, it can progress to dead in weeks to months
What are the clinical manifestations or signs of endocarditis?
- New heart murmur
- Splenomegaly
- Various skin lesions
- Retinal lesions
What are splinter hemorrhages?
1-2mm brown linear streaks in the nail bed associated with endocarditis
What are roth spots?
Retinal hemorrhages associated with endocarditis
What are Janeway lesions?
Painless lesions on palms or soles of feet associated with endocarditis
What are Osler nodes?
Painful subcutaneous nodules in the pads of the digits associated with endocarditis
*Thought to be caused by vasculitis or septic embolization
What bacteria are associated with infective endocarditis?
S. viridans= less virulent & associated with subacute endocarditis
S. aureus= more virulent & associated with acute
List the characteristics of S. aureus.
Gram + cocci in clusters
Catalase +
Coagulase +
List the characteristics of S. viridans.
Gram + cocci in chains
a-hemolytic
Optochin resistant
No Lancefield group
Specifically, what 2 S. aureus species are most associated with subacute endocarditis?
S. mitis
S. salivarius
What are the risk factors for infective endocarditis?
1) Susceptible cardiovascular substrate i.e. patient with prosthetic heart valve or previous damage to heart valve
2) Source of bacteremia
3) IV drug use
4) HIV (esp. HIV + IV drug use)
5) Immunosuppressed with central venous catheter
6) Hemodialysis
Describe the pathophysiology of endocarditis.
- Cardiac abnormalities create sites for bacterial attachment
- Vegetations are formed at attachment sites & are composed of platelets, fibrin, bacteria, & inflammatory cells
- These vegetations can break off an become “septic emboli” that damage brain, kidney, & spleen
How is bacterial endocarditis diagnosed?
Major criteria:
- History & physical examination
- 95% have bacteremia that will test positive with blood culture
- Imaging evidence of endocardial involvement
*Minor criteria involve identifying risk factors, fever, and skin lesions
How is endocarditis treated?
1) Aggressive initial antimicrobidal therapy
2) Prolonged antimicrobial therapy
