The Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) have recently revised the susceptibility interpretive criteria of oxyimino-β-lactams and carbapenems for Enterobacteriaceae. According to the new criteria, susceptibility testing results are sufficient to detect extended-spectrum β-lactamases (ESBLs) and carbapenemases; it is not necessary to perform ESBL or carbapenemase detection tests for therapeutic purposes. Thus, it has been recommended that these related tests be performed only for infection control. These changes in the susceptibility guidelines are supported by some clinical cases and the results of pharmacodynamic and animal studies. However, differences still exist between the breakpoints established by the CLSI and EUCAST with regard to some oxyimino-β-lactam and carbapenem antibiotics, in particular, the breakpoints for ceftazidime and cefepime established by the CLSI are higher than those established by the EUCAST. Also, similar numbers of successful and unsuccessful cases have been reported regarding the use of cephalosporins or carbapenems in treating infections caused by low-minimal inhibitory concentration (MIC) ESBL-producers or low-MIC carbapenemase-producers. Finally, routine susceptibility test methods are not as accurate as research-purpose test methods, showing differences in MICs ranging approximately from 1 to 8 μg/mL. In conclusion, it is strategically prudent to continue to perform ESBL and carbapenemase detection tests and to avoid the use of the corresponding antimicrobial agents for the treatment of ESBL- or carbapenemase-producing bacterial infections. (Ann Clin Microbiol 2013;16:111-119)