EUCAST rapid antimicrobial susceptibility testing of blood cultures positive for Escherichia coli or Klebsiella pneumoniae: experience of three laboratories in Italy

Sir, Recently, EUCAST developed a rapid antimicrobial susceptibility testing (RAST) method for direct use on positive blood culture (BC) samples, which relies on EUCAST standard disc diffusion (DD) methodology and allows inhibition zone reading within 4–8 h of BC positivity. Shortly after the first description of the method in 20181 and before its publication at the beginning of 2020,2 we concertedly began to familiarize ourselves with RAST in the clinical microbiology laboratories of three large hospitals from Northern or Central Italy. Although RAST is applicable to most important bloodstream infection (BSI) pathogens (including Gram-negative and Gram-positive species) against a definite (albeit clinically comprehensive) number of antimicrobial agents,2 we focused on Escherichia coli and Klebsiella pneumoniae, because both species represent the bulk of BSI aetiologies (with highly diversified antimicrobial resistance mechanisms) encountered in clinical settings. We herein report on EUCAST RAST results for BCs consecutively collected between...