Multicenter Evaluation of an MIC-Based Aztreonam and Ceftazidime-Avibactam Broth Disk Elution Test

Harley Harris, Lili Tao, Emily B. Jacobs, Yehudit Bergman, Ayomikun Adebayo, Tsigedera Tekle, Shawna Lewis, Ashley Dahlquist, Taylor C. Abbey, Eric Wenzler, Romney Humphries, Patricia J. Simner

Research output: Contribution to journalArticlepeer-review


Due to limited therapeutic options, there is a clinical need to assess the in vitro activity of the combination of aztreonam (ATM) and ceftazidime-avibactam (CZA) to guide the therapeutic management of multidrug-resistant (MDR) Gram-negative organism infections. We set out to develop a practical MIC-based broth disk elution (BDE) method to determine the in vitro activity of the combination ATM-CZA using readily available supplies and compare it to reference broth microdilution (BMD). For the BDE method, a 30-mg ATM disk, a 30/20-mg CZA disk, both disks in combination, and no disks were added to 4 separate 5-mL cation-adjusted Mueller-Hinton broth (CA-MHB) tubes, using various manufacturers. Three testing sites performed both BDE and reference BMD testing of bacterial isolates in parallel from a single 0.5 McFarland standard inoculum and after overnight incubation, assessed them for growth (not susceptible) or no growth (susceptible) at a final concentration of 6/6/4 mg/mL ATM-CZA. During the first phase, the precision and accuracy of the BDE were analyzed by testing 61 Enterobacterales isolates at all sites. This testing yielded 98.3% precision between sites, with 98.3% categorical agreement and 1.8% major errors (ME). During the second phase, at each site, we evaluated unique, clinical isolates of metallo-b-lactamase (MBL)-producing Enterobacterales (n = 75), carbapenem-resistant Pseudomonas aeruginosa (n = 25), Stenotrophomonas maltophilia (n = 46), and Myroides sp. (n = 1). This testing resulted in 97.9% categorical agreement, with 2.4% ME. Different results were observed for different disk and CA-MHB manufacturers, requiring a supplemental ATM-CZA-not-susceptible quality control organism to ensure the accuracy of results. The BDE is a precise and effective methodology for determining susceptibility to the combination ATM-CZA.

Original languageEnglish (US)
JournalJournal of clinical microbiology
Issue number5
StatePublished - May 2023


  • CLSI
  • antimicrobial susceptibility testing
  • aztreonam
  • broth disk elution
  • ceftazidime-avibactam
  • multicenter study

ASJC Scopus subject areas

  • Microbiology (medical)


Dive into the research topics of 'Multicenter Evaluation of an MIC-Based Aztreonam and Ceftazidime-Avibactam Broth Disk Elution Test'. Together they form a unique fingerprint.

Cite this