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.
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.
Thomson
K S
KS
Center for Research in Anti-Infectives and Biotechnology, Creighton University School of Medicine, Omaha, Nebraska 68178, USA. kstaac@creighton.edu
Sanders
C C
CC
Moland
E S
ES
D016971:Citrobacter freundii / Q000201:enzymology; D004754:Enterobacter / Q000201:enzymology; D004755:Enterobacteriaceae / Q000187:drug effects / Q000201:enzymology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004926:Escherichia coli / Q000201:enzymology; D007709:Klebsiella / Q000201:enzymology; D008826:Microbial Sensitivity Tests; D012706:Serratia marcescens / Q000201:enzymology; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000096:biosynthesis*
D004791:Enzyme Inhibitors; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases