[The distribution of minimal inhibitory concentrations of recently introduced cephalosporins in multiresistant strains of Escherichia coli, Proteus mirabilis and Klebsiella spec. as revealed by zone sizes of a standardized agar diffusion test (author's transl)].

Strains of a species were divided into two groups according to the number of resistances (less than or equal to 4, greater than or equal to 5) using 10 standard chemotherapeutics regularly examined, the new cephalosporins not being among them. These groups of less than or equal to 4- and greater than or equal to 5-fold resistant strains were compared for each cephalosporin tested (Fig. 1). The most different distributions of zone diameters (of both groups) were seen in Cephalothin, whereas in Cefoxitin and - with little limitations - also in Cefuroxime in the main these distributions did not differ; they covered the same field. The distributions of Cefaclor and Cefamandole took an intermediate position. With respect to the two groups similar observations were made for E. coli, proteus mirabilis and Klebsiella spec. The differences between the two groups were most marked in Klebsiella strains. E. coli exhibited the smallest differences (Fig 1). On the assumption that the distribution of zone diameters reflect that of MIC's it can be concluded that nearly all of the Cefaclor- and Cefamandole-sensitive multiresistant strains have more elevated MIC's than those with only less than or equal to 4 resistances. On the other hand it must not be expected that MIC'S OF Cefoxitin and Cefuroxim are rising in multiresistant strains. It could be demonstrated that the different qualities of the recently introduced cephalosporins revealed in multiresistant strains can be explained by different dependences on mechanisms of Cephalothin-resistance (Fig. 2). This resistance is much more frequent in greater than or equal to 5-fold resistant strains. Recommendations for clinical use derived from these results are discussed.