Figure 3
DSTs with the randomly prepared inocula of clinical isolates. (A) The distribution of random inoculum sizes prepared without measuring cell density. Four researchers randomly prepared 110 clinical isolates, and the bacterial CFUs were counted afterward. The highest inoculum size was 1.1 × 108 CFU/mL and the lowest was 1.4 × 105 CFU/mL. (B) DST results with the randomly prepared inocula with clinical isolates. The DSTs for the first-line drugs were performed with the randomly prepared inocula in the DAC system, and the DST results were compared with those of the L-J method. There were high agreement rates between the two systems. (C) More severe inoculum effect in the ESBL-positive strain. Antibiotic-inactivating enzymes in the culture medium caused a more severe inoculum effect with respect to the use of cefepime according to the inoculum size. In the broth microdilution method, the inoculum effect in the ESBL-negative E. coli ATCC 25922 strain was over 107 CFU/mL, and the inoculum effect of the ESBL-positive E. coli strain was over 106 CFU/mL. However, in the DAC system, there was no inoculum effect with either the ESBL-negative or ESBL-positive strains from 105 CFU/mL to 107 CFU/mL.
