Evaluation of the chromogenic Cica-beta-Test for detecting extended-spectrum, AmpC and metallo-beta-lactamases.
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.
Livermore
D M
DM
Antibiotic Resistance Monitoring and Reference Laboratory, Health Protection Agency Centre for Infections, 61 Colindale Avenue, London NW9 5EQ, UK. david.livermore@hpa.org.uk
Warner
M
M
Mushtaq
S
S
D001426:Bacterial Proteins / Q000378:metabolism*; D002511:Cephalosporins / Q000378:metabolism*; D002863:Chromogenic Compounds / Q000378:metabolism*; D020563:Gammaproteobacteria / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D001618:beta-Lactamases / Q000378:metabolism*
D001426:Bacterial Proteins; D002511:Cephalosporins; D002863:Chromogenic Compounds; C487639:HMRZ 86; C048795:AmpC beta-lactamases; D001618:beta-Lactamases