Incidence of Extended-Spectrum-β-Lactamase-Producing Escherichia coli and Klebsiella pneumoniae Isolates That Test Susceptible to Cephalosporins and Aztreonam by the Revised CLSI Breakpoints

The incidence of aztreonam and cephalosporin susceptibility, determined using the revised CLSI breakpoints, for extendedspectrum-beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae isolates was evaluated. Our analysis showed that results for aztreonam and/or> 1 cephalosporin were reported as susceptible or intermediate for 89.2% of ESBLproducing E coli isolates (569/638 isolates) and 67.7% of ESBL-producing K. pneumoniae isolates (155/229 isolates).