Background and Rationale for Revised Clinical and Laboratory Standards Institute Interpretive Criteria (Breakpoints) for Enterobacteriaceae andPseudomonas aeruginosa:I. Cephalosporins and Aztreonam

Widespread resistance in Enterobacteriaceae and Pseudomonas aeruginosa to cephalosporin and monobactam antibiotics due to extended-spectrum β-lactamases (ESBLs) has resulted in the need for reassessment of the interpretative criteria (breakpoints) established for these agents more than 2 decades ago. Following extensive evaluation, the Clinical and Laboratory Standards Institute recently adopted and published new breakpoints for these agents for use in clinical laboratories and provided updated recommendations for use of the ESBL screening test. This paper summarizes the background and supportive rationale for new interpretative criteria for cephalosporins and aztreonam for testing Enterobacteriaceae.