When comparing antibiotic activities, it might be of interest to study parameters other than minimal inhibitory concentrations (MIC's). Specific activity of beta-lactams on bacterial cell wall makes it possible to determine radiolabelled diaminopimelic acid (DAP) incorporation in growing cultures. We have studied the effects of various concentrations of cefalotin , cefotaxime, latamoxef (moxalactam) and ceftiolene (42 980 RP) on DAP incorporation in 6 strains of E. coli, E. cloacae and S. aureus. Drug concentration which inhibits 90 % of radioactivity incorporation (CII 90) was found to vary from 0.1 X MIC to 3 X MIC. This fact suggests that beta-lactam action on cell wall synthesis and/or structure and MIC's are not always strictly correlated.
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