Ceftolozane/Tazobactam Susceptibility in ESBL-Producing Enterobacterales: Insights from the SMART Program 2020-2022...

Surveillance data on ceftolozane/tazobactam (C/T) activity against extended-spectrum β-lactamase-producing Enterobacterales (ESBL-E) in China remains limited. This study summarized species- and source-specific C/T susceptibility patterns using isolates collected through the Study for Monitoring Antimicrobial Resistance Trends (SMART) China program (2020-2022).

Non-duplicate Enterobacterales isolates from bloodstream, intra-abdominal, respiratory, and urinary tract infections (BSI, IAI, RTI, UTI) were collected in 18 tertiary hospitals. Minimum inhibitory concentrations (MICs) were determined by broth microdilution and interpreted using CLSI M100 2025. ESBL-E were defined as ceftriaxone-nonsusceptible (i.e, intermediate or resistant) and carbapenem-susceptible Enterobacterales (CSE), with species-specific adjustments for Morganella, Proteus, and Providencia; carbapenem-resistant isolates were analyzed separately. Annual rate was analyzed to reveal the resistance trend from 2020 to 2022.

All Enterobacterales isolates meeting inclusion criteria were analyzed; isolation rate is reported by species for the seven most prevalent, which together comprised 93.5% of isolates; the remaining genera contributed to the aggregate totals. Overall susceptibility of Enterobacterales to C/T was high. Among CSE, susceptibility was 92.2%, with 83.1% in ESBL‑E. By infection site, C/T susceptibility among ESBL‑E was 88.3% in UTI, 85.3% in BSI, 79.9% in RTI, and 77.4% in IAI. Susceptibility was highest in ESBL-Escherichia coli (90.6%) and lower in Klebsiella pneumoniae (72.9%) and Enterobacter cloacae (55.3%). Among ESBL-E, the MIC distribution for C/T was centered at ≤0.5-2 mg/L, corresponding to an overall susceptibility of 83.1%; resistant isolates (MIC ≥8 mg/L) were uncommon (12.4%) but clustered in selected species and sources.

C/T susceptibility among ESBL-E was high in E. coli but substantially lower and more variable in K. pneumoniae and E. cloacae; the aggregate order-level susceptibility of 83.1% should not be relied upon to guide empiric therapy when Klebsiella or Enterobacter infection is suspected. Continued surveillance and susceptibility testing are essential to support evidence-based antimicrobial use.