Performance of direct-from-blood-culture disk diffusion antibiotic susceptibility testing and its impact on antibiotic adjustment in bloodstream infections at a Malaysian tertiary center

ABSTRACT Delayed antibiotics increase mortality in bloodstream infection (BSI). Direct-from-blood-culture disk diffusion antibiotic susceptibility testing (dAST) forecasts susceptibility earlier than conventional susceptibility testing (cAST). The study aimed to evaluate dAST performance and its impact on antibiotic adjustment in BSI. In this Malaysian single-center prospective study, dAST was performed and interpreted according to breakpoints by Clinical and Laboratory Standards Institute (CLSI) guidelines. The turnaround time (TAT), categorical agreements (CA), and predictive values of dAST for susceptibility by cAST were determined among positive blood cultures (PBC) between November 2022 and November 2023. The active and WHO AWaRe antibiotics administered before and after dAST results were compared. Of the 318 PBCs, the median of TAT was earlier than cAST by 35 hours. The CA for 3,561 organism-antibiotics combinations was 91.5%, with 3.6% very major errors (VME), 3.3% major errors (ME), and 5.2% minor errors (mE). The dAST achieved CA above 90% for Staphylococcus aureus with cefoxitin (98.5%), Pseudomonas aeruginosa with ceftazidime (100%), and Acinetobacter baumannii with ampicillin/sulbactam (100%). For Enterobacterales, most combinations were above 90%, including ampicillin (95.1%), ceftriaxone (95.7%), and meropenem (95.7%), though those of the aminopenicillin/inhibitor combinations were above 80%. Most errors were attributed to mEs. Among 159 BSI, the prescribing of active antibiotics improved significantly following dAST (73.0% versus 89.3%, P < 0.001) but not WHO Access antibiotics (35.8% versus 35.2%, P = 0.188). dAST had good CAs for most antibiotics, allowing earlier improvement in active antibiotics. The modest change in WHO Access antibiotics prescribing reveals practice gaps in need of antimicrobial stewardship.IMPORTANCEGlobal deaths attributable to antimicrobial resistance are rising. Hence, rapid susceptibility testing is essential for timely antibiotic de-escalation to mitigate antimicrobial resistance (AMR) development from exposure to broad-spectrum antibiotics. Compared to the costly advanced technology, direct disk diffusion from blood culture (diffusion antibiotic susceptibility testing [dAST]) is an affordable method that can be quickly adopted. However, the reliability of dAST in informing susceptibility was mainly reported from Western countries and scarcely from other regions, including Southeast Asia, where the AMR burden is high. This study from Malaysia adds insights into the performance of dAST and the potential to apply it in similar resource-limited settings from the same region. Furthermore, assessing the dAST's influence on antibiotic prescribing identifies the gap in implementation to guide areas of improvement for optimizing clinical utility.