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Introduction <p>Metallo-β-lactamase (MBL)-producing <i>Enterobacterales</i> are increasing in frequency and treatment options are limited. Aztreonam/avibactam (AZA) and aztreonam (ATM) plus ceftazidime/avibactam (CZA) showed activities against these organisms. <i>Escherichia coli</i> with PBP3 insertions (YRIN, YRIK) showed decreased activities to AZA and have been linked with treatment failures.</p> Methods <p>We used well-characterized global collections of MBL-producing <i>Enterobacterales</i> (<i>n</i> = 86) to evaluate if MICs generated by AZA MIC Test Strips (MTS) could be used as substitute testing for ATM-CZA Broth Disk Elution (ATM-CZA BDE). We also determined if AZA (breakpoint of 4/4 µg/ml) or ATM-CZA BDE could detect <i>E. coli</i> with PBP-3 insertions.</p> Results <p>The AZA MTS at ≤ 2/4µg/ml and ≥ 8/4µg/ml) showed 100% categorical agreement with ATM-CZA BDE but was less labour-intensive and more cost-effective. A strain with AZA MIC of 4/4 µg/ml tested not susceptible with ATM-CZA BDE, resulting in a very major error rate of 1/9 (11%). ATM-CZA BDE and AZA MICs (1–4&#xa0;µg/ml) reported 76% (42/55) of <i>E. coli</i> with <i>bla</i><sub>NDMs</sub> that contained YRIK/YRIN insertions, as susceptible.</p> Conclusions <p>AZA MIC Test Strips can reliably predict ATM-CZA BDE results, except for strains with MICs of 4/4 µg/ml. ATM-CZA BDE failed to detect most of <i>E. coli</i> with PBP-3 insertions. <i>E. coli</i> with AZA MICs ranging from 1/4 to 4/4 µg/ml could be screened for PBP-3 insertions, and patients infected with such isolates, should be monitored for possible treatment failures with AZA or ATM-CZA.</p>

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Aztreonam plus ceftazidime/avibactam broth disk elution test: failure to detect Escherichia coli with PBP-3 insertions

  • 期刊论文

  • 发表日期：

    2026年1月24日

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  • Gisele Peirano,
  • Sydney D. Walker,
  • Mary S. Duong,
  • Kelsey Frank,
  • Jan M. Delantar,
  • Luiz Lisboa,
  • Wilson W. Chan,
  • Johann D. D. Pitout

摘要

Introduction

Metallo-β-lactamase (MBL)-producing Enterobacterales are increasing in frequency and treatment options are limited. Aztreonam/avibactam (AZA) and aztreonam (ATM) plus ceftazidime/avibactam (CZA) showed activities against these organisms. Escherichia coli with PBP3 insertions (YRIN, YRIK) showed decreased activities to AZA and have been linked with treatment failures.

Methods

We used well-characterized global collections of MBL-producing Enterobacterales (n = 86) to evaluate if MICs generated by AZA MIC Test Strips (MTS) could be used as substitute testing for ATM-CZA Broth Disk Elution (ATM-CZA BDE). We also determined if AZA (breakpoint of 4/4 µg/ml) or ATM-CZA BDE could detect E. coli with PBP-3 insertions.

Results

The AZA MTS at ≤ 2/4µg/ml and ≥ 8/4µg/ml) showed 100% categorical agreement with ATM-CZA BDE but was less labour-intensive and more cost-effective. A strain with AZA MIC of 4/4 µg/ml tested not susceptible with ATM-CZA BDE, resulting in a very major error rate of 1/9 (11%). ATM-CZA BDE and AZA MICs (1–4 µg/ml) reported 76% (42/55) of E. coli with blaNDMs that contained YRIK/YRIN insertions, as susceptible.

Conclusions

AZA MIC Test Strips can reliably predict ATM-CZA BDE results, except for strains with MICs of 4/4 µg/ml. ATM-CZA BDE failed to detect most of E. coli with PBP-3 insertions. E. coli with AZA MICs ranging from 1/4 to 4/4 µg/ml could be screened for PBP-3 insertions, and patients infected with such isolates, should be monitored for possible treatment failures with AZA or ATM-CZA.