Tenover FC, Emery SL, Spiegel CA, Bradford PA, Eells S, Endimiani A, Bonomo RA, McGowan JE
Identification of Plasmid-Mediated AmpC {beta}-lactamases in Escherichia coli, Klebsiella pneumoniae, and Proteus species Can Potentially Improve Reporting of Cephalosporin Susceptibility Testing Results. [JOURNAL ARTICLE]
J Clin Microbiol 2008 Nov 26.
The goal of this study was to determine if the interpretations of extended-spectrum (ESC) and advanced-spectrum (ASC) cephalosporins for isolates of Enterobacteriaceae would be impacted by the results of aminophenylboronic acid (APBA) testing. Fifty-three isolates of Escherichia coli, 21 Klebsiella species, and 6 Proteus species that were resistant to at least one extended-spectrum cephalosporin were tested by disk diffusion with ceftazidime and cefotetan disks with and without aminophenylboronic acid (APBA). Ceftazidime disks with and without clavulanic acid (CLAV) were also tested to confirm extended-spectrum beta-lactamase (ESBL) carriage. Twenty-nine (36.3%) isolates were only APBA-test positive, 27 were only CLAV-test positive, 2 were positive with both substrates, and 22 were negative with both substrates. Thirteen (41.9%) of the 31 APBA-test positive isolates (all E. coli) tested susceptible to cefotaxime, ceftriaxone, or ceftazidime. Since clinical data suggest that AmpC-producing isolates should be reported as resistant to all ESCs, APBA testing can be helpful in identifying such organisms. Screening for AmpC-producing organisms using non-susceptibility to cefoxitin and amoxicillin-clavulanate was less specific than APBA testing; it identified ESBL as well as AmpC-producing organisms. Only 18 of 31 APBA-positive isolates were positive by PCR for an AmpC beta-lactamase gene. Thus, testing with APBA could improve the accuracy of reporting ESCs, especially for E. coli. However, results of APBA and CLAV testing did not correlate well for isolates containing both AmpC beta-lactamases and ESBLs. Thus, additional data are needed before making formal recommendations on changing ASC results.
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