- tubes for sampling blood for microbiological cultures
- detection of circulating microorganisms in bacteraemia and septicaemia
DESCRIPTION Types of blood culture bottles and blood volumes required:
- Yellow top – paediatric aerobic (0.5–4 mL blood)
- Green top – adult aerobic (5–10 mL blood)
- Orange top – anaerobic (5–10 mL blood)
- Black top – mycobacteria (5–10 mL blood)
- Silver top – mycoplasma (3–5 mL blood)
- special nutrient broths
- contain agents which act as anticoagulants and neutralise the natural bactericidal action of blood
- cooked meat or a reducing agent is added to anaerobic bottles to aid growth of anaerobic bacteria
- ratio of blood to broth is usually 10 mL to 200 mL
METHOD OF USE Blood culture collection
- sterile blood sampling (i.e. hand hygiene, sterile dressing pack, sterile gloves and clean skin with chlorhexidine)
- take from fresh venepuncture or alternatively newly inserted peripheral cannulae and central lines
- if line sepsis is suspected cultures should be taken from the central line and peripherally
- blood placed into aerobic and anaerobic culture medium
- remove dust cap from culture bottles and top swabbed with alcohol (and allowed to dry) before blood is injected
- maximum yield if the tube is neither under nor over-filled (e.g. 9 mL in adult tubes)
- fill blood culture tubes before other blood tubes
OTHER INFORMATION Number of cultures
- two sets of cultures from separate sites before starting antibiotics is ideal
- 3 cultures having a 96% sensitivity in detecting bacteraemia
- more than 4 cultures generally offers little additional benefit
- additional cultures may be beneficial if suspected endocarditis or pre-existing antimicrobial use
- antibiotics should not be withheld pending culture in critically ill septic patients
Incubation and culture
- incubation at room temperature initially to avoid killing temperature sensitive bacteria
- turbid appearance may indicate microbial growth — bottles are placed into holders with light passed through — an alarm sounds when significant microbial growth interrupts the passage of light through bottles
- all samples are subcultured onto agar plates to test purity, allow organism identification and for antibiotic sensitivity testing
- suspect if single, random cultures of Bacillus species, coagulase-negative staphylococci or diphtheroids
- less likely if grown in more than one bottle (another reason for taking multiple cultures from separate sites)
- associated with venesection
- needle stick injury
- contamination may lead to unnecessary antibiotic use (e.g. skin flora)
- failure of microbial growth due to inadequate quantity of blood in the bottle or wrong culture bottles used
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.