In vitro activity of beta-lactam antibiotics against CTX-M-producing Escherichia coli

  • M. Tärnberg
  • Å. Östholm-Balkhed
  • H.-J. Monstein
  • A. Hällgren
  • H. Hanberger
  • L. E. Nilsson


Beta-lactam antibiotics have been discussed as options for the treatment of infections caused by multiresistant extended-spectrum beta-lactamase (ESBL)-producing bacteria if the minimum inhibitory concentration (MIC) is low. The objective of this study was to investigate the in vitro activity of different beta-lactam antibiotics against CTX-M-producing Escherichia coli. A total of 198 isolates of E. coli with the ESBL phenotype were studied. Polymerase chain reaction (PCR) amplification of CTX-M genes and amplicon sequencing were performed. The MICs for amoxicillin–clavulanic acid, aztreonam, cefepime, cefotaxime, ceftazidime, ceftibuten, ertapenem, imipenem, mecillinam, meropenem, piperacillin–tazobactam, and temocillin were determined with the Etest. Susceptibility was defined according to the breakpoints of the European Committee on Antimicrobial Susceptibility Testing (EUCAST). MIC50 and MIC90 values were calculated. Isolates from CTX-M group 9 showed higher susceptibility to the beta-lactam antibiotics tested than isolates belonging to CTX-M group 1. More than 90% of the isolates belonging to CTX-M group 9 were susceptible to amoxicillin–clavulanic acid, ceftazidime, ceftibuten, piperacillin–tazobactam, and temocillin. The susceptibility was high to mecillinam, being 91%, regardless of the CTX-M group. All isolates were susceptible to imipenem and meropenem, and 99% to ertapenem. This study shows significant differences in susceptibility to different beta-lactam antibiotics among the CTX-M-producing E. coli isolates and a significant difference for many antibiotics tested between the CTX-M-producing groups 1 and 9. The good in vitro activity of other beta-lactam antibiotics compared to carbapenems indicate that clinical studies are warranted in order to examine the potential role of these beta-lactam antibiotics in the treatment of infections caused by multiresistant ESBL-producing E. coli.


Minimum Inhibitory Concentration Piperacillin Clavulanic Acid Aztreonam Ertapenem 
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This work was supported by the Medical Research Council of Southeast Sweden.

Transparency declaration

Nothing to declare.

Author contributions

MT, ÅÖB, H-JM, AH, HH, and LEN participated in the conception, design, and drafting of the manuscript, and final approval of the version to be published. MT was responsible for the laboratory work, analysis, statistical calculations, and interpretations. MT, ÅÖB, and LEN were responsible for the clinical strain collection.


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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • M. Tärnberg
    • 1
  • Å. Östholm-Balkhed
    • 1
    • 2
  • H.-J. Monstein
    • 1
    • 3
  • A. Hällgren
    • 1
    • 2
  • H. Hanberger
    • 1
    • 2
  • L. E. Nilsson
    • 1
  1. 1.Department of Clinical and Experimental Medicine, Faculty of Health SciencesLinköping UniversityLinköpingSweden
  2. 2.Department of Infectious DiseasesLinköping University HospitalLinköpingSweden
  3. 3.Department of Clinical MicrobiologyLinköping University HospitalLinköpingSweden

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