Evaluation of the chromogenic Cica-beta-Test for detecting extended-spectrum, AmpC and metallo-beta-lactamases

J Antimicrob Chemother. 2007 Dec;60(6):1375-9. doi: 10.1093/jac/dkm374. Epub 2007 Oct 3.

Abstract

Background: Extended-spectrum, metallo- and AmpC beta-lactamases usually are sought subsequently to susceptibility testing, meaning that producers are not identified until 72 h after a clinical specimen is taken. Chromogenic tests might usefully shorten this delay, and we investigated the Cica-beta-Test for this purpose.

Methods: Reference and clinical strains with known beta-lactamases, or controls, were grown with a cefpodoxime disc to promote conservation of resistance. The cultures were then tested with nitrocefin and with the Cica-beta-Test, which examines for hydrolysis of the chromogenic oxyimino-cephalosporin HMRZ-86 with and without specific inhibitors of extended-spectrum, metallo- and AmpC beta-lactamases.

Results: were scored, as colour changes from yellow to red, with the tester blinded to the strain identity and the mechanism(s) present. Results Proportions of extended-spectrum, metallo- and AmpC beta-lactamase producers correctly identified by the Cica-beta-Test were 85%, 77% and 72%, respectively. Such performance should be achievable if testing colonies from a primary culture plate, 24 h after a specimen was taken. Greater precision, albeit at more delay, would be achieved if results were read in conjunction with antibiogram data available 48 h after the specimen was taken. Limitations were frequent confusion of Klebsiella oxytoca hyperproducing K1 enzyme with AmpC hyperproducers, and that isolates with NMC-A or KPC carbapenemases were wrongly inferred to have AmpC enzymes.

Conclusions: The Cica-beta-Test has the potential to provide useful therapeutic guidance, identifying isolates with potent beta-lactamases and informing early therapy; it will also help to monitor beta-lactamase epidemiology among multiresistant strains.

Publication types

  • Evaluation Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / metabolism*
  • Cephalosporins / metabolism*
  • Chromogenic Compounds / metabolism*
  • Gammaproteobacteria / drug effects
  • Gammaproteobacteria / enzymology*
  • Gammaproteobacteria / growth & development
  • Humans
  • Microbial Sensitivity Tests / methods
  • beta-Lactamases / metabolism*

Substances

  • Bacterial Proteins
  • Cephalosporins
  • Chromogenic Compounds
  • HMRZ 86
  • AmpC beta-lactamases
  • beta-Lactamases