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Antimicrobial Agents and Chemotherapy, June 1999, p. 1393-1400, Vol. 43, No. 6
0066-4804/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Use of Microdilution Panels with and without beta -Lactamase Inhibitors as a Phenotypic Test for beta -Lactamase Production among Escherichia coli, Klebsiella spp., Enterobacter spp., Citrobacter freundii, and Serratia marcescens

Kenneth S. Thomson,* Christine C. Sanders, and Ellen Smith Moland

Center for Research in Anti-Infectives and Biotechnology, Creighton University School of Medicine, Omaha, Nebraska 68178

Received 7 August 1998/Returned for modification 23 November 1998/Accepted 31 March 1999

Over the past decade, a number of new beta -lactamases have appeared in clinical isolates of Enterobacteriaceae that, unlike their predecessors, do not confer beta -lactam resistance that is readily detected in routine antibiotic susceptibility tests. Because optimal methodologies are needed to detect these important new beta -lactamases, a study was designed to evaluate the ability of a panel of various beta -lactam antibiotics tested alone and in combination with beta -lactamase inhibitors to discriminate between the production of extended-spectrum beta -lactamases, AmpC beta -lactamases, high levels of K1 beta -lactamase, and other beta -lactamases in 141 isolates of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae, Enterobacter aerogenes, Citrobacter freundii, and Serratia marcescens possessing well-characterized beta -lactamases. The microdilution panels studied contained aztreonam, cefpodoxime, ceftazidime, cefotaxime, and ceftriaxone, with and without 1, 2, and 4 µg of clavulanate per ml or 8 µg of sulbactam per ml and cefoxitin and cefotetan with and without 8 µg of sulbactam per ml. The results indicated that a minimum panel of five tests would provide maximum separation of extended-spectrum beta -lactamase high AmpC, high K1, and other beta -lactamase production in Enterobacteriaceae. These included cefpodoxime, cefpodoxime plus 4 µg of clavulanate per ml, ceftazidime, ceftriaxone, and ceftriaxone plus 8 µg of sulbactam per ml. Ceftriaxone plus 2 µg of clavulanate per ml could be substituted for cefpodoxime plus 4 µg of clavulanate per ml without altering the accuracy of the tests. This study indicated that tests with key beta -lactam drugs, alone and in combination with beta -lactamase inhibitors, could provide a convenient approach to the detection of a variety of beta -lactamases in members of the family Enterobacteriaceae.

* Corresponding author. Mailing address: Center for Research in Anti-Infectives and Biotechnology, Creighton University School of Medicine, 2500 California Plaza, Omaha, NE 68178. Phone: (402) 280-1881. Fax: (402) 280-1225. E-mail: kstaac{at}creighton.edu.

Antimicrobial Agents and Chemotherapy, June 1999, p. 1393-1400, Vol. 43, No. 6
0066-4804/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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Copyright © 1999 by the American Society for Microbiology. All rights reserved.