Comparison of inhibitory and bactericidal activities of cefoperazone + sulbactam against Pseudomonas aeruginosa strains, from 1992 to 1994

In this study: inhibitory and bactericidal activities of cefoperazone + sulbactam against Pseudomonas aeruginosa strains were determined in two studies first in 1992 and second in 1994. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values were determined by following the microdilution method recommended by NCCLS (Approved Standard M7-A2 1990) protocol. P. aeruginosa strains were isolated from different clinical materials. The results of the studies were then compared to point out if the difference between MIC and MBC values were significant and if there was resistance development following two years of use. In the first study in 1992: MIC90 and susceptibility percentage were 8 μgr/ml and 99%; MBC90 and susceptibility percentage were 64 μg/ml and 90%, respectively. In the second study: MIC90 was 128 μg/ml; susceptibility percentage was 71%; MBC90 and susceptibility percentage were 256 μg/ml and 28%, respectively. When the susceptibilities were compared according to MIC90 and MBC90 values; the difference was not significant in 1992 (χ²=0.43, p>0.05), but significant in 1994 (χ²=18.8, p<0.001). The difference between the susceptibilities according to MIC90 values was statistically significant (χ²=4.6, p<0.05), where according to MBC90 values very significant (χ²=32.56, p<0.001). These results indicated that the antipseudomonal activity of cefoperazone+sulbactam reduced since 1992 to 1994 and MBC determinations were necessary to evaluate the antibiotic susceptibility of Paeruginosa rather than MIC determinations.