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Antimicrob Agents Chemother. 2015 Dec;59(12):7483-8. doi: 10.1128/AAC.01804-15. Epub 2015 Sep 21.

In Vivo Evolution of CMY-2 to CMY-33 β-Lactamase in Escherichia coli Sequence Type 131: Characterization of an Acquired Extended-Spectrum AmpC Conferring Resistance to Cefepime.

Author information

1
Institute for Infectious Diseases, University of Bern, Bern, Switzerland Graduate School for Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland.
2
Case Western Reserve University, Cleveland, Ohio, USA.
3
Research Service, Louis Stokes VA Medical Center, Cleveland, Ohio, USA.
4
Division of Infectious Diseases, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, USA.
5
Institute for Infectious Diseases, University of Bern, Bern, Switzerland.
6
Department of Infectious Diseases, Bern University Hospital and University of Bern, Bern, Switzerland.
7
Research Service, Louis Stokes VA Medical Center, Cleveland, Ohio, USA Division of Infectious Diseases and HIV Medicine, Department of Medicine, University Hospitals Case Medical Center, Cleveland, Ohio, USA Infectious Diseases Section, Medical Service, Louis Stokes Cleveland Department of Veterans Affairs Medical Center, Cleveland, Ohio, USA Department of Pharmacology, Molecular Biology and Microbiology, Case Western Reserve University, Cleveland, Ohio, USA bonomo@va.gov aendimiani@gmail.com.
8
Institute for Infectious Diseases, University of Bern, Bern, Switzerland bonomo@va.gov aendimiani@gmail.com.

Abstract

Cefepime is frequently prescribed to treat infections caused by AmpC-producing Gram-negative bacteria. CMY-2 is the most common plasmid-mediated AmpC (pAmpC) β-lactamase. Unfortunately, CMY variants conferring enhanced cefepime resistance have been reported. Here, we describe the evolution of CMY-2 to an extended-spectrum AmpC (ESAC) in clonally identical Escherichia coli isolates obtained from a patient. The CMY-2-producing E. coli isolate (CMY-2-Ec) was isolated from a wound. Thirty days later, one CMY-33-producing E. coli isolate (CMY-33-Ec) was detected in a bronchoalveolar lavage fluid sample. Two weeks before the isolation of CMY-33-Ec, the patient received cefepime. CMY-33-Ec and CMY-2-Ec were identical by repetitive extragenic palindromic-PCR (rep-PCR), being of hyperepidemic sequence type 131 (ST131) but showing different β-lactam MICs (e.g., cefepime MIC, 16 and ≤ 0.5 μg/ml for CMY-33-Ec and CMY-2-Ec, respectively). Identical CMY-2-Ec isolates were also found in a rectal swab. CMY-33 differs from CMY-2 by a Leu293-Ala294 deletion. Expressed in E. coli strain DH10B, both CMYs conferred resistance to ceftazidime (≥ 256 μg/ml), but the cefepime MICs were higher for CMY-33 than CMY-2 (8 versus 0.25 μg/ml, respectively). The kcat/Km or inhibitor complex inactivation (kinact)/Ki app (μM(-1) s(-1)) indicated that CMY-33 possesses an extended-spectrum β-lactamase (ESBL)-like spectrum compared to that of CMY-2 (e.g., cefoxitin, 0.2 versus 0.4; ceftazidime, 0.2 versus not measurable; cefepime, 0.2 versus not measurable; and tazobactam, 0.0018 versus 0.0009, respectively). Using molecular modeling, we show that a widened active site (∼ 4-Å shift) may play a significant role in enhancing cefepime hydrolysis. This is the first in vivo demonstration of a pAmpC that under cephalosporin treatment expands its substrate spectrum, resembling an ESBL. The prevalence of CMY-2-Ec isolates is rapidly increasing worldwide; therefore, awareness that cefepime treatment may select for resistant isolates is critical.

PMID:
26392491
PMCID:
PMC4649241
DOI:
10.1128/AAC.01804-15
[Indexed for MEDLINE]
Free PMC Article

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