Microbiology of the Cardiovascular System

Question 1

• What is the definition of infective endocarditis?

Answer 1

Bacterial (or fungal) infection of a heart valve or area of the endocardium

Question 2

• Is the incidence higher in male or female patients?

Answer 2

Same

Question 3

• In what way has the epidemiology of IE changed in the antibiotic era?

Answer 3

before - rheumatic fever used to be the main RF but now not so much.

Question 4

Native Valve IE:

2) associated with what conditions?
3) what non-virulent family bacteria normally causes it?

Answer 4

2) congenital heart disease causing floppy valves
rheumatic heart disease
degenerative valve lesions: MR, AR, AS, MS (associated with old age).
3) alpha haemolytic streptococci = strep. mutans, strep. sanguis)

Question 5

Prosthetic Valve Endocarditis

1) accounts for what portion of IE?
2) what type of bacteria?

Answer 5

1) 1-5%

2) coagulase -ve staphylococci

Question 6

IVDU - asssociated

1) how?
2) peak age?
3) right or left side more common?
4) main bacteria?
5) fungus on citrus fruit that causes this how?
6) tricuspid, aortic and mitral - which one is affected more?

Answer 6

1) mechanical damage to valve from the glass and talc drugs are cut with + bugs from non-sterile injection = damage + bacteraemia = IE.
2) 30
3) right sided infection - when you inject stuff - goes into the veins so bugs can travel to right side first.
4) Staph.aureus (as it lives on skin)
5) candida tropicalis - citric acid is often needed to dissolve heroin so lemons are often used.
6) tricuspid (50% )
aortic (25%)
mitral (25%)

Question 7

Nosocomial IE

1) what is it?
2) is it more common right or left sided?

Answer 7

1) hospital acquired - often by doctor’s putting in IV lines, central lines,
2) right

Question 8

Are the bugs that cause IE usually gram +ve or –ve?

Answer 8

80% are Gram +ve

Question 9

• Why might you get a culture negative IE?

Answer 9

1. The endocarditis isn’t actually infective, it’s because of something autoimmune like lupus (so it’s not technically an IE)
2. Because we just aren’t able to grow it in the lab (e.g. Q fever – the bug is intracellular and the mediums in the lab are cell free
3. Because GPs have given a course of antibiotics that has wiped out the bacteraemia, meaning we can’t take blood and grow the bug. Note that even though the antibiotics wipe out the bacteraemia, they do not kill the bugs in the vegetation.

Question 10

what other way can you diagnose a culture negative IE?

Answer 10

PCR

Question 11

• What is a classical culture negative cause of IE?

Answer 11

Q fever (Coxiella burnetti)

Question 12

• Hence, what types of IE are diagnosed using PCR on valve tissue

Answer 12

1. Bartonella spp.

2. Trypheryma whipplei

Question 13

• What procedures pose the greatest risk for causing the transient bacteraemia?

Answer 13

1. Dental procedures
2. Catheterisation
3. Endoscopy

Question 14

• What will the urine analysis of someone with IE be like?

Answer 14

o Proteinuria

o Microscopic haematuria

Question 15

• We don’t need to know how to treat IE because it’s very specific to the individuals infection, but there are some principles we should know about. Hence, what are some of these key things to bear in mind when treating IE?

• what spectrum of Abx do you give?
• what synergistic drug do you give?
• how long do you give Abx?

Answer 15

o Figure out what bug is causing the infection before starting antibiotics
o Treat with the narrowest spectrum antibiotic you can
o Use low-dose gentamycin for synergy (synergistic drug = something that boosts the effectiveness of another drug)
o Treat for at least 4 weeks (but some types like Q fever require years of treatment)

Question 16

• Are antibiotics used prophylactically for anyone with an underlying heart condition who is about to have a procedure?

Answer 16

They used to be, but there’s no actual evidence-base for this. Hence, the NICE guidelines changed and we no longer give prophylactic antibiotics to people undergoing procedures even if they have a heart defect.