Modifiable Risk Factors for the Emergence of Ceftolozane-tazobactam Resistance

Pranita D. Tamma*, Stephan Beisken, Yehudit Bergman, Andreas E. Posch, Edina Avdic, Sima L. Sharara, Sara E. Cosgrove, Patricia J. Simner

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


Background: Ceftolozane-tazobactam (TOL-TAZ) affords broad coverage against Pseudomonas aeruginosa. Regrettably, TOL-TAZ resistance has been reported. We sought to identify modifiable risk factors that may reduce the emergence of TOL-TAZ resistance. Methods: Twenty-eight consecutive patients infected with carbapenem-resistant P. aeruginosa isolates susceptible to TOL-TAZ, treated with ≥72 hours of TOL-TAZ, and with P. aeruginosa isolates available both before and after TOL-TAZ exposure between January 2018 and December 2019 in Baltimore, Maryland, were included. Cases were defined as patients with at least a 4-fold increase in P. aeruginosa TOL-TAZ MICs after exposure to TOL-TAZ. Independent risk factors for the emergence of TOL-TAZ resistance comparing cases and controls were investigated using logistic regression. Whole genome sequencing of paired isolates was used to identify mechanisms of resistance that emerged during TOL-TAZ therapy. Results: Fourteen patients (50%) had P. aeruginosa isolates which developed at least a 4-fold increase in TOL-TAZ MICs(ie, cases). Cases were more likely to have inadequate source control (29% vs 0%, P = .04) and were less likely to receive TOL-TAZ as an extended 3-hour infusion (0% vs 29%; P = .04). Eighty-six percent of index isolates susceptible to ceftazidime-avibactam (CAZ-AVI) had subsequent P. aeruginosa isolates with high-level resistance to CAZ-AVI, after TOL-TAZ exposure and without any CAZ-AVI exposure. Common mutations identified in TOL-TAZ resistant isolates involved AmpC, a known binding site for both ceftolozane and ceftazidime, and DNA polymerase. Conclusions: Due to our small sample size, our results remain exploratory but forewarn of the potential emergence of TOL-TAZ resistance during therapy and suggest extending TOL-TAZ infusions may be protective. Larger studies are needed to investigate this association.

Original languageAmerican English
Pages (from-to)E4599-E4606
JournalClinical Infectious Diseases
Issue number11
StatePublished - 1 Dec 2021
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2020 The Author(s). Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved.


  • AmpC
  • DNA polymerase
  • PBP3
  • antimicrobial resistance
  • ceftazidime-avibactam


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