1984 Volume 37 Issue 9 Pages 1701-1713
The MICs and MBCs of cefotaxime (CTX), desacetylcefotaxime (Des-CTX) and ceftriaxone (CTRX) were determined in relation to 4 of the principal bacterial species which cause meningitis, i.e., S. pneumoniae, S. agalactiae, H. influenzae and E. coli. These tests were performed using final inocula of 108cells/ml and 108cells/ml. Comparison was made with the MIC and MBC values of benzylpenicillin (PCG) and ampicillin (ABPC).
1. Against 25 strains of S. pneumoniae, the MIC90 values with inocula levels of 108 and 106cells/ml were as follows: CTX, 0.05 and 0.024μg/ml; Des-CTX, 0.39 and 0.20μg/ml; CTRX, 0.10 and 0.05μg/ml, respectively; and PCG, <0.012μg/ml at both size. Similarly, the MBC90 values were: CTX, 0.01 and 0.05μg/ml; Des-CTX, 0.78 and 0.39μg/ml; CTRX, 0.20 and 0.10μg/ml; and PCG, 0.024 and 0.012μg/ml, respectively. It is thus apparent that PCG showed the lowest values for both the MIC and MBC, followed by CTX, CTRX and then Des-CTX. Against 25 strains of S. agalactiae, the MICH values with inocula of 108 and 106cells/ml were as follows: CTX, 0.05 and 0.05μg/ml; Des-CTX, 0.39 and 0.20μg/ml; CTRX, 0.10 and 0.05μg/ml; and PCG, 0.39 and 0.20μg/ml, respectively. Similarly, the MBC90 values of Des-CTX were 0.78 and 0.39μg/ml, while the other 3 antibiotics showed the same values with both the 108 and 108cells/ml inocula: 0.10μg/ml for CTX, 0.20μg/ml for CTRX and 0.39μg/ml for PCG. Accordingly, CTX showed the lowest values, followed by CTRX and then PCG being about the same as Des-CTX.
Against 25 strains of H. influenzae, the MIC90 values with inocula levels of 108 and 106cells/ml were as follows: CTX, 0.10 and 0.05μg/ml; Des-CTX, 0.39 and 0.39μg/ml; CTRX, 0.10 and 0.05μg/ml; and ABPC, 50 and 6.25μg/ml, respectively. Similarly, the MBC90 values were: CTX, 0.20 and 0.10μg/ml; Des-CTX, 1.56 and 1.56μg/ml; CTRX, 0.39 and 0.20μg/ml; and ABPC, >100 and 50μg/ml, respectively. Accordingly, in terms of the MIC90, CTX and CTRX showed the same values, but in terms of the MBC90 CTX was superior. In both cases, Des-CTX and ABPC were third and fourth, respectively. Four (16%) of these strains were found to be,β-lactamase producing and to be resistant to ABPC, but they showed the same susceptibility to CTX, Des-CTX and CTRX as the ABPC-sensitive strains.
Against 25 strains of E. coli, the MIC90 values of CTRX with inocula of 108 and 106cells/ml were 0.10 and 0.05μg/ml, respectively, while the other 3 antibiotics showed no differences as a function of the inoculum size: CTX, 0.05μg/ml; Des-CTX, 0.78μg/ml; and ABPC, > 100μg/ml. Similarly, the MBC90 values were the same for each drug at both the 108 and 108 inoculum size: CTX, 0.20μg/ml; Des-CTX, 3.13μg/ml; CTRX, 0.39μg/ml; and ABPC, >100μg/ml. The order of potency, in descending order was thus CTX, CTRX, Des-CTX, ABPC. Five (20%) of these strains were found to be resistant to ABPC, but they showed the same susceptibility to CTX, Des-CTX and CTRX as the ABPC-sensitive strains.
2. CTX showed the same or superior antibacterial activity, compared to CTRX against each of the 4 tested bacterial species. There was not even 1 strain which was found to be more sensitive to CTRX than to CTX. In addition, comparing CTX and PCG, PCG was superior against all strains of S. pneumoniae, and CTX was superior against all strains of S. agalactiae.
3. Comparison of the MICs and the MBCs for each of the strains reveals that the MBCs of each of the antibiotics were usually twice as large as the MICs in the cases of S. pneumoniae and S. agalactiae, 2-4 times as large in the case of H. influenzae, and 4 times as large in the case of E. coli.
