D M Livermore1, M Warner, S Mushtaq. 1. Antibiotic Resistance Monitoring and Reference Laboratory, Health Protection Agency Centre for Infections, 61 Colindale Avenue, London NW9 5EQ, UK. david.livermore@hpa.org.uk
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.
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-cephalosporinHMRZ-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.
Authors: Mark A Fisher; Paul D Stamper; Kristine M Hujer; Zachary Love; Ann Croft; Samuel Cohen; Robert A Bonomo; Karen C Carroll; Cathy A Petti Journal: J Med Microbiol Date: 2009-06 Impact factor: 2.472