Infective Endocarditis and Other Cardiac Infections Flashcards
What is bacteraemia?
AKA septicaemia - this is not a clinical diagnosis (indicates there is a focus of infection elsewhere in the body)
Presence of bacteria in the bloodstream (blood is normally sterile); it is potentially fatal and, if not treated, patient may develop septic shock and die
Blood culture bottles?
There are two:
Aerobic
Anaerobic
The fluid is a growth medium and the yellow base indicates a +ve bottle
Why must skin be cleaned before blood culture collection?
To prevent contamination of the sample with skin flora
Briefly, how does the blood culture machine work?
Incubates cultures for 5 days and detects any CO2 produced that changes the base
Most significant growth occurs within 48-72 hours
Incubation of Staph. aureus?
Overnight incubation on different agar plates produces pale gold/white colony of Staph. aureus
Appearance of Strep. viridans colony?
Gram +ve cocci in chains
α-haemolysis produces a greenish tinge around the colony
Why are antibiotic discs used?
To determine which antibiotics the bacteria is sensitive/resistance to
3 questions to ask oneself with blood culture results?
- Is this organism in the blood cultures likely to be a skin contaminant?
- If not - where (in the patient) is it coming from?
- Does the patient need antibiotics and, if so, which antibiotics?
What infections does Strep. pneumoniae cause?
Pneumonia
Meningitis
What infections do E. coli, Klebsiella and other coliforms cause?
Urinary tract
Gut infections
What infections does Staph. aureus cause?
Skin and wound infection
Bone/joint infection
Endocarditis
What is Staph. epidermidis?
Commonest “coagulase-negative Staphylococcus”
Infections caused by Staph. epidermidis?
Often a skin contaminant, but can infect prosthetic material, e.g: IV line infections and prosthetic heart valve/joints
Cautions with blood cultures?
Should take more than one set of blood cultures to confirm
What are the diphtheroids and give an example?
Skin contaminants, e.g: Corynebacterium sp.
What is infective endocarditis?
Infection of the endothelium of the heart valves that is potentially fatal (often diagnosed late)
Types of infective endocarditis?
Acute - present suddenly unwell
Sub-acute - more insidious/gradual onset of symptoms
Predisposing factors to infective endocarditis?
Heart valve abnormality:
Calcification/sclerosis in elderly
Congenital heart disease
Post-rheumatic fever (infection with Group A Strep. - neurological damage to heart valves)
Prosthetic heart valve
IV drug users (particulate matter can roughen up valves, part. tricuspid valve, making infection easier)
IV lines
Pathogenesis of endocarditis?
Heart valve damaged
Turbulent blood flow over roughened endothelium
Platelets/fibrin deposited
Bacteraemia (may be very transient), e.g: from dental treatment
Organisms settle in fibrin/platelet thrombi, becoming a microbial vegetation
What are septic emboli?
Infected vegetations are friable and break off, becoming lodged in the next capillary bed they encounter, causing haemorrhage or abscesses - potentially fatal
Valves commonly infected?
Usually left side of heart, i.e: mitral and aortic valves
In drug users (inject into groin), tricuspid valve is often affected
Organisms causing endocarditis of native (non-prosthetic) valves?
Staph. aureus (most common) - aggressive organism that is a usually the cause of acute endocarditis
Viridans streptococci
Enterococcus sp.
Staphylococcus epidermidis
Unusual organisms causing endocarditis?
“Atypical” organisms - Bartonella, Coxiella burnetti (Q-fever), Chlamydia, Legionella, Mycoplasma, Brucella
Gram negatives
Fungi
Acute endocarditis: presenting symptoms?
Overwhelming sepsis and cardiac failure (inference with heart valve function)
