Rapid AST in bloodcultures

Rapid AST directly from blood culture bottles

EUCAST has developed a method for rapid AST (reading at 4, 6 or 8h incubation) directly from positive blood culture bottles (RAST).
Following the initial development, published in 2019, a clinical trial in 55 laboratories was performed and published in 2020.

These are the essential steps in the RAST method:

  • direct inoculation of disk diffusion plates (MH, MH-F) using 100 - 150 ┬ÁL directly from a positive blood culture bottle (BD, bioMerieux and Thermo Fisher).
  • no centrifugation or dilution of the inoculum - streak plates as for standard EUCAST disk diffusion.
  • shortened incubation - 4, 6 and 8 hours with breakpoints adapted to each incubation time.
  • zone diameters are read from the front of the plate after removal of the lid.
  • breakpoints for each species and each reading time.
  • identity of species must be known prior to interpretation of AST results.
  • the method is validated for the following species.

    • Escherichia coli
    • Klebsiella pneumoniae
    • Pseudomonas aeruginosa
    • Staphylococcus aureus
    • Streptococcus pneumoniae
    • Enterococcus faecalis and Enterococcus faecium
    • Acinetobacter baumannii (added 2 May, 2019)

  • a positive blood culture bottle should be processed 0 - 18 hours after the positive signal.
  • each species has its own TAB in the table and each reading time (4, 6 and 8 hours) its own section.
  • not all zone diameters can be read after 4 hours. Read again after 6 and 8 hours. Incubation can not be extended over night. If needed, perform a regular AST overnight.
  • read zone diameters ONLY when an obvious zone edge can be identified - otherwise re-incubate and read after 6 or 8 hours. 
  • the breakpoint table is specific for EUCAST Rapid AST - do not use the regular breakpoint table and do not use for rapid AST on an inoculum prepared from colonies.

 

Ongoing work (to be finalised 2020 - 21):

  • EUCAST is currently evaluating continued incubation beyond 8 hours. 

 

Implementing RAST from blood culture bottles

If you have implemented, or aim to implement, RAST according to the EUCAST method, please send an email stating the name, town and country of your laboratory, and tell us if you were successful or encountered difficulties. Contact EUCAST via the subject related contact form.