TABLE 1.

Quantification of the inoculum effect on meropenem MIC within the CLSI allowable inoculum range^a

^aAll 8 strains tested were resistant to meropenem with MICs ranging from 8 to 32 μg ml⁻¹ at the target CLSI inoculum: 4 strains had an MIC of 8; 3 had an MIC of 16; and 1 had an MIC of 32 μg ml⁻¹. Notably, relative changes in MIC appeared to be independent of the original MIC, as also observed in results shown in Fig. 1. The shaded region represents inocula within the CLSI allowable inoculum range of 2 × 10⁵ to 8 × 10⁵ CFU ml⁻¹.

^bMICs between 2-fold dilutions were rounded to the next-highest dilution per CLSI guidelines (26). The MIC at 4.9 × 10⁵ CFU ml⁻¹ was defined as the CLSI inoculum. CI, confidence interval.

^cMinor errors are the percentages of tests resulting in categorical misclassification as intermediate at the indicated inoculum density. All minor errors occurred in strains whose MIC at the target inoculum was 8 μg ml⁻¹.