Use of microdilution panels with and without β-lactamase inhibitors as a phenotypic test for β-lactamase production among Escherichia coli, Klebsiella spp., Enterobacter spp., Citrobacter freundii, and Serratia marcescens

• Published in: Antimicrobial agents and chemotherapy 1999-06, Vol.43 (6), p.1393-1400
• Main Authors: THOMSON, K. S, SANDERS, C. C, MOLAND, E. S
• Format: Article
• Language: English
• Subjects: Bacteriological methods and techniques used in bacteriology; Bacteriology; beta-Lactamase Inhibitors; beta-Lactamases - biosynthesis; Biological and medical sciences; Citrobacter freundii - enzymology; Enterobacter - enzymology; Enterobacteriaceae - drug effects; Enterobacteriaceae - enzymology; Enzyme Inhibitors - pharmacology; Escherichia coli; Escherichia coli - enzymology; Fundamental and applied biological sciences. Psychology; Klebsiella; Klebsiella - enzymology; Microbial Sensitivity Tests; Microbiology; Serratia marcescens - enzymology; Susceptibility
• ISSN: 0066-4804; 1098-6596
• DOI: 10.1128/aac.43.6.1393

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 microg of clavulanate per ml or 8 microg of sulbactam per ml and cefoxitin and cefotetan with and without 8 microg 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 microg of clavulanate per ml, ceftazidime, ceftriaxone, and ceftriaxone plus 8 microg of sulbactam per ml. Ceftriaxone plus 2 microg of clavulanate per ml could be substituted for cefpodoxime plus 4 microg 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.