JAC Advance Access published online on October 3, 2007
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkm374
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Evaluation of the chromogenic Cica-ß-Test for detecting extended-spectrum, AmpC and metallo-ß-lactamases
Antibiotic Resistance Monitoring and Reference Laboratory, Health Protection Agency Centre for Infections, 61 Colindale Avenue, London NW9 5EQ, UK
Received 4 June 2007; returned 17 July 2007; revised 3 September 2007; accepted 4 September 2007
* Corresponding author. Tel: +44-20-8327-7223; Fax: +44-20-8327-6264; E-mail: david.livermore{at}hpa.org.uk
Background: Extended-spectrum, metallo- and AmpC ß-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-ß-Test for this purpose.
Methods: Reference and clinical strains with known ß-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-ß-Test, which examines for hydrolysis of the chromogenic oxyimino-cephalosporin HMRZ-86 with and without specific inhibitors of extended-spectrum, metallo- and AmpC ß-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 ß-lactamase producers correctly identified by the Cica-ß-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-ß-Test has the potential to provide useful therapeutic guidance, identifying isolates with potent ß-lactamases and informing early therapy; it will also help to monitor ß-lactamase epidemiology among multiresistant strains.
Key Words: ß-lactamase detection , chromogenic cephalosporin , HMRZ-86
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