Influence of sulbactam content on susceptibility testing results of cefoperazone/sulbactam combination disks / 中华检验医学杂志

ABSTRACT

Objective To study the discrepancy influence of the sulbactam content on susceptibility testing results of cefoperazone/sulbactam combination disks.Methods Agar dilution method was used to determine MICs of cefoperazone,cefoperazone/sulbactam(21 and 11),and disk diffusion was used to detect the zone diameters of cefoperazone,cefoperazone/sulbactam(75/30 and 75/75μg/disk)disks against 534 clinical gram-negative isolates.The discrepancy within the results of MICs,zore diameters,the method of agar dilution and disk diffusion was analyzed.Results By standard agar dilution method,MIC_(50) of cefoperazone,cefoperazone/sulbactam(21 and 11)were 32,16,16μg/ml,and MIC_(90) of those were ≥256.128,64 μg/ml respectively.No statistic discrepancy was found for MICs between the ratios of 21 and 11 combination by Wilcoxon ranks test(Z=-0.248,P=0.804).Susceptibility rate,resistance rate,and intermediate rate with 75/30μg disk were 55.3%,24.5%and 20.2%respectively,which were similar to those determined by agar dilution method.Susceptibility rate,resistance rate,and intermediate rate(I%)with 75/75μg disk were 72.5%,12.4% and 15.1% respectively,compared with the susceptibility rate from 75/30μg disk was 17.2% higher.Statistic discrepancy were tested by paired t-test (t=21.613,P＜0.01)with two groups of whole strains' zone diameters from 75/30μg and 75/75μg disks,and resulting in the difference of susceptibility or resistance rates for ESBL-producing strains,Acinetobacter bauamnnii and Enterobacteriaceae without ESBL tested isolates.On the contrary,for Pseudomonas aeruginosa,Stenotrophomonas maltophilia and ESBL negative isolates,the zone diameters discrepancy was not statistically significant between the results from 75/30μg and 75/75μg disks.Conclusions There is no statistic discrepancy between the susceptibility results from cefoperazone/sulbactam(21 or 11 ratios)in dilution method and in diffusion method with 75/30μg disk.When the 75/75μg disk is used to be tested for ESBL-producing strains,Acinetobacter bauamnnii and other Enterobacteriaceae,the results should be shown with sulbactam content.