Differences among moxalactam, cefoperazone, and cefotaxime in activity against multiple-antibiotic-resistant gram-negative bacteria.

In vitro evaluations have shown that moxalactam, cefoperazone, and cefotaxime, three new beta-lactam antibiotics, have certain potency and antibacterial spectral characteristics in common. Results of parallel tests of these antibiotics against routine clinical isolates have suggested that these compounds could be tested with one disk that is representative of this spectral class. The key requirement for this class concept in disk testing is that there be no bacterial resistance mechanism that can operate against one, but not all, members of the proposed class. The results of an 11-center study of approximately 500 isolates of multiple-antibiotic-resistant Enterobacteriaceae responsible for nosocomial infections illustrated that cross-resistance to moxalactam, cefoperazone, and cefotaxime is highly variable from center to center. Thus, the spectral class concept of disk susceptibility testing would be inappropriate for this group of drugs.