BACKGROUND

Important guide: G_90_Info_10_A Common Blood culture Gram stains and implications 1Sep22 amended 1May25

Documentation!

• Always record your clinician discussion about a case in a large personal diary or preferably on the electronic pathology record for the patient’s sample if this exists.
• Categorise and record the clinical relevance of the positive culture – a standard template to be shared soon.

Improve blood culture collection practice

• Ensure that your clinicians know how to collect blood cultures correctly – pathology registrars/ residents can get involved with training . See this collection instruction as a guide.
• Check out this guide before you start a collection training program – Blood culture collection tutorial notes 25 Aug 2019
• Calculate your blood culture contamination rates regularly and identify locations that require follow-up training (if rate of contamination > 5%)

Phone notification – use ISBAR 

• I introduce yourself – “I am the Pathology Registrar” and make sure you know who you are talking to – ask their name and record it in your notes.
• S “I am calling you about a positive blood culture on your patient x.”
• B Ask the clinician for some background on the patient – what is wrong with them, what antimicrobials are they on already? What doses are being used?
• A Work out your assessment of the situation; is this a significant blood culture isolate? If so are the antibiotics the patient is on ok for the job? Are the doses appropriate?
• R Make a recommendations- these might include- change of drug, dose, advice that you will call them when the susceptibilities are ready etc.

NB. At the end of the call, check that the clinician has got the correct message – ask him/her to repeat back what they have heard. 

Remember, in order for your advice to be respected, some formality in your communication style with the clinician is worthwhile – be systematic as above.  The clinician needs to know that you are really on their side (and the patient’s).

FIRST CALL- Positive Gram stain result available

• visit the lab every morning to check for new positive cultures and results of identification and susceptibility for previous events
• where possible access results from other micro benches for the patient to know what had grown
• white cell count – often helps to know this to help judge the significance of the event
• also check liver function tests for adults with Gram negative sepsis (? cholestatic picture c/w biliary sepsis)

Gram stain shows Gram Positive Cocci resembling staph

• await 4 hour initial tube coagulase reaction from the bottle sediment. Only contact doctor if coagulase positive.
• need to form an idea of likely source of infection; is there a surgically drainable collection, is it endocarditis, is an intravascular line responsible? S. aureus in blood cultures is rarely a contaminant, though this occurs more often in children.
• empiric treatment-wise, if MRSA accounts for more than 20% of positive S. aureus blood culture presentations, flucloxacillin or cefazolin is not going to be a good idea and an alternative is required –  intravenous vancomycin most usually. In situations where vancomycin not currently available, seek advice about an alternative.

GPC (strep)

• Two possibilities- Streptococcus species or Enterococcus species.
• Generally IV benzylpenicillin or amoxycillin will be suitable. If it sounds like a lobar pneumonia and GPC (diplococci) resembling pneumococcus then ensure that dose of benzylpenicillin is sufficient- 1.8g 4hrly for severe cases best.

Gram positive rod

• Possibilities include- Bacillus (usually large rectangular shape), Clostridium, Corynebacterium (smaller, clumps in chinese character type appearance), Listeria.
• Most frequently- contamination – however, have to be careful that Listeria and B. anthracis are properly considered during workup.

Gram negative rod

• Most usually, these represent significant isolates. See Part 2.
• Correlate with other lab results (e.g. urine culture, liver function tests)

Gram negative diplococcus

• Assume that this is Neisseria meningitidis although occasionally Moraxella or Acinetobacter will look similar. Acinetobacter– see environmental Gram negatives within second posting.

Yeast

• Most frequently will represent Candida species. Line sepsis (central line) most often.  Haematology patients may get disseminated disease. Intravenous drug users may also present with candidaemia.  Cryptococcus may also be grown from blood in a patient with disseminated disease.