Bacteraemia and Blood cultures Flashcards
What are the types of bacteremia? give examples.
Transient bacteremia (Tooth brushing, biopsy)
Intermittent bacteremia (Abscess)
Persistent/sustained bacteremia (intravascular)
How is bacteremia confirmed?
Blood cultures methods:
Nutrient broths
Aerobic and anaerobic cultures
Antibiotic absorbing resins
Specialised culture bottles (optimal recovery of fastidious organisms and optimising yield with small volume using paediatric BC bottle)
How is contamination risk minimised in blood cultures?
Specimen is collected and palpated with gloved finger.
Skin is cleansed and top of culture bottle is swapped with alcohol swipe
What is the expected contamination rate of skin flora in samples?
1 - 3 %
What types of bacteria are often contaminating the sample from skin flora?
CoNS
Corynebacterium
Bacillus
Propionobacterium
What disinfectant solutions can contaminate the sample?
Benzalkonium chloride
Povidone - Iodine
How much blood is taken to maximise yield?
Age volume protocol:
If younger than 10 years 1 ml per year of life
If older than 10 years 20ml (10ml per bottle) [if veins dont give much blood less than 20ml should be taken]
What was the yield of <5ml blood?
70% vs 90% when >5mls
How many sets should be taken to maximise yield?
3 sets returns a >98% sensitivity
Why is multiple sets better?
Multiple sets allow determination of clinical relevance of isolates usually viewed as contaminants
How is a blood culture done?
Bacteria added to bottle
Bottle put into incubator
Laser detects turbidity when it is sufficient
Bottle removed from incubator and investigated
What is done to bottle after incubation?
It is flagged and removed
Fluid is withdrawn
Gram stain
Plate onto SBA, CHOC, and MAC agar as appropriate
anaerobic plate if anaerobic plate is positive
Definitive ID test when subcultures growing 24 - 48 hours and then onto antibiotic sensitivity testing
If bacteria is a fastidious bacteria needing long term incubation what is done?
Lab is alerted and incubation period is extended to 5 days
What tests can be used to quickly identify a bacteria?
Mass spectroscopy
Direct tube coagulase and other reapid phenotypic tests
FISH (fluorescence in situ hybridisation) probes
PCR and NAAT methods (identify MSSA or MRSA in hours)
panPCR
