False equivalence: differences in the in vitro activity of ampicillin-sulbactam and amoxicillin-clavulanate in several Enterobacterales species.
Academic Article
Overview
abstract
BACKGROUND AND OBJECTIVES: The β-lactam/β-lactamase inhibitor combinations ampicillin-sulbactam (SAM) and amoxicillin-clavulanate (AMC) are frequently used to treat Enterobacterales infections and are often assumed to be interchangeable, leading some clinical microbiology laboratories to report antimicrobial susceptibility testing (AST) results for only one of these agents. Given differences in β-lactamase inhibition between sulbactam and clavulanate, we hypothesized that the in vitro activities of SAM and AMC may differ. METHODS: To understand the prevalence of discordant SAM and AMC susceptibility results in Enterobacterales species, we analysed AST results obtained by broth microdilution (MicroScan WalkAway, Beckman Coulter) for Enterobacterales isolates recovered from clinical specimens between 2018 and 2022 at an academic medical centre in New York City. RESULTS: Percentages of isolates susceptible to SAM were lower than percentages susceptible to AMC for Escherichia coli (58.1% versus 85.4% of 23,746 isolates, P < 0.0001), Klebsiella pneumoniae group (76.7% versus 88.7% of 6,630, P < 0.0001), Proteus mirabilis (88.0% versus 95.4% of 3,185, P < 0.0001) and Klebsiella oxytoca (69.6% versus 90.7% of 890, P < 0.0001). Isolates of E. coli, K. pneumoniae group and P. mirabilis with susceptibility profiles consistent with ESBL production (ceftriaxone resistant and cefoxitin susceptible) were more likely to be susceptible to AMC but not susceptible to SAM than isolates without this susceptibility phenotype (E. coli, 38% versus 27%, P < 0.0001; K. pneumoniae group: 40% versus 10%, P < 0.0001; P. mirabilis: 24% versus 6%, P < 0.0001). CONCLUSIONS: The high prevalence of SAM-not susceptible, AMC-susceptible isolates supports reporting AST results for both SAM and AMC to maximize options for antimicrobial therapy and to support antimicrobial stewardship.
