Practical implications of lowered break-points for enterobacteria

Lowering break-points of beta- lactam antibiotics greatly contributed to optimize their use. This is obvious with the third and fourth generation cephalosporins and aztreonam in relation to the extended spectrum beta- lactamase (ESBL)producing enterobacteria. Up to 2011, antibiogram interpretation used to consider any ESBL-positive strain as "intermediate" or "resistant" to these antibiotics. Since this date, breakpoints of beta- lactam antibiotics has been lowered, allowing ESBL-positive strains to be considered as susceptible, given that the minimum inhibitory concentration (MIC) (whose measurement is mandatory) is lower than or equal to the lowest break-point. The resistance/susceptibility pattern is sometimes dissociated regarding these antibiotics. Expected benefits of this recent approach include the decrease in carbapenem use in ESBL-positive infections. Administration of third and fourth generation cephalosporins and aztreonam to treat ESBL-producing strains, appearing susceptible based on the disk diffusion test, requires measurement of the exact MIC. Patients with ESBL-positive infections treated using these antibiotics should receive high-dosage regimens and combinations with other classes of antibiotics like aminoglycosids. However, despite a significant decrease, the current break-points of carbapenems (imipenem and meropenem) likely remain too high.