Five-year availability of early antibiotic-specific susceptibility results for Enterobacterales and their clinical actionability in intensive care

Abstract Early availability of microbiological identification and antimicrobial susceptibility of Enterobacterales may support timely antimicrobial decision-making. The objectives were (i) to describe the cumulative antimicrobial susceptibility patterns of Enterobacterales ; (ii) to evaluate the ability of the BD Phoenix M50 antimicrobial susceptibility testing (AST) system to generate same-day results in Enterobacterales ; (iii) to assess the clinical impact of rapid Enterobacterales identification by MALDI-TOF combined with the same-day AST by M50 in an intensive care unit (ICU) setting. A retrospective laboratory-based analysis to achieve objectives (i) and (ii) and a prospective observational study conducted in ICU to achieve objective (iii) were performed. 36,641 isolates were analyzed with Imipenem (IMP), Meropenem (MEM), Ceftazidime–Avibactam (CZA) and Amikacin (AMK) showing the highest activity based on susceptibility rates. At six hour-incubation of the M50 panel, a substantial proportion of results were available for resistant isolates (93.5% of AST results for Ampicillin-resistant Escherichia coli isolates were available). At 11 h of panel incubation, the upper operational limit for same-day AST reporting, AST results were more often available for susceptible than resistant isolates (in E. coli , available AST results exceeded 95% for 22 of 25 antibiotics among susceptible isolates, compared with 13 of 25 among resistant isolates). Carbapenems and CZA presented the lower proportion of available results at 11 h. In the ICU cohort ( n = 23), rapid MALDI-TOF identification accounted for 26.7% of all therapeutic interventions and AST results reported by 22:00 h for 73.3%. No additional antimicrobial therapy changes were documented following availability of the complete AST panel on the subsequent day. IMP, MEM, CZA and AMK showed the highest activity against Enterobacterales . Rapid MALDI-TOF identification combined with same-day M50 AST reporting enabled antimicrobial optimization for Enterobacterales infections without increasing costs or laboratory workload.