Direct ertapenem disk screening method for identification of KPC-producing Klebsiella pneumoniae and Escherichia coli in surveillance swab specimens

J Clin Microbiol. 2010 Mar;48(3):836-41. doi: 10.1128/JCM.01988-09. Epub 2010 Jan 13.


Klebsiella pneumoniae carbapenemase (KPC) production in Gram-negative bacilli is an increasing problem worldwide. Rectal swab surveillance is recommended as a component of infection prevention programs, yet few screening methods are published. We compared detection of KPC-producing Klebsiella pneumoniae and Escherichia coli in surveillance specimens by 2 methods: (i) inoculation of swabs in tryptic soy broth containing 2 microg/ml imipenem followed by plating to MacConkey agar (MAC) (method 1) and (ii) streaking swabs on MAC onto which a 10-microg ertapenem disk was then placed (method 2). Simulated rectal swab specimens of challenge isolates from a collection of well-characterized K. pneumoniae and E. coli strains and salvage rectal swab specimens collected from patients at 4 different health care facilities over a 7-month period were tested. The gold-standard comparator was bla(KPC) PCR testing of isolates. Method 1 detected 4/9 (44%) KPC-positive challenge isolates. By method 2, 9/9 KPC-positive challenge isolates exhibited zones of inhibition of < or = 27 mm; all KPC-negative isolates exhibited zones of inhibition greater than 27 mm. The sensitivity and specificity of method 1 for detection of KPC-positive K. pneumoniae and E. coli in 149 rectal swab specimens were 65.6% (95% confidence interval [CI], 46.8% to 80.8%) and 49.6% (95% CI, 40.3% to 58.9%), respectively. With method 2, a zone diameter of < or = 27 mm had a sensitivity of 97.0% (95% CI, 82.5% to 99.8%) and specificity of 90.5% (95% CI, 83.3% to 94.9%) for detection of KPC in rectal swab specimens. Direct ertapenem disk testing is simpler, more sensitive, and more specific than selective broth enrichment with imipenem for detection of KPC-producing K. pneumoniae and E. coli in surveillance specimens.

Publication types

  • Comparative Study
  • Evaluation Study

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • Bacterial Proteins / biosynthesis*
  • Carrier State / microbiology
  • Ertapenem
  • Escherichia coli / enzymology*
  • Escherichia coli / isolation & purification
  • Escherichia coli Infections / microbiology*
  • Humans
  • Klebsiella Infections / microbiology*
  • Klebsiella pneumoniae / enzymology*
  • Klebsiella pneumoniae / isolation & purification
  • Mass Screening / methods
  • Microbial Sensitivity Tests / methods
  • Rectum / microbiology
  • Sensitivity and Specificity
  • beta-Lactamases / biosynthesis*
  • beta-Lactams / pharmacology*


  • Anti-Bacterial Agents
  • Bacterial Proteins
  • beta-Lactams
  • beta-Lactamases
  • carbapenemase
  • Ertapenem