Problems with detection of beta-lactam resistance among nonfastidious gram-negative bacilli.

The single most important aspect of any susceptibility test is the accurate detection of resistance, because resistance carries a strong prediction of therapeutic failure. However, the accurate detection of resistance has been difficult in tests performed with gram-negative organisms producing certain beta-lactamases and in tests with the new beta-lactam drug/beta-lactamase inhibitor combinations. These problems are due to limitations in the design of studies performed to establish test parameters, and these problems can be avoided if a new predictor panel approach is used. This, coupled with the use of special tests to detect resistance mechanisms, could optimize the accurate identification of beta-lactam resistance in gram-negative bacteria.