TABLE 3.
Inter- and intralaboratory comparisons of cefepime-enmetazobactam MICs (enmetazobactam concentrations fixed at 8 μg/ml) and inhibition zone diameters with 30/20-μg disks for E. coli ATCC 35218 obtained in the CLSI M23 tier 2 study to establish QC ranges
| Assay measurea | No. of occurrences by medium lotb
|
No. of occurrences by disk lot |
No. of occurrences by laboratoryc
|
Total no. of occurrences | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| A | B | C | A | B | A | B | C | D | E | F | G | H | ||
| MIC (μg/ml) | ||||||||||||||
| 0.008 | 49 | 9 | 5 | 8 | 4 | 6 | 6 | 4 | 7 | 49 | ||||
| 0.016 | 59 | 5 | 41 | 20 | 11 | 9 | 12 | 9 | 12 | 9 | 23 | 105 | ||
| 0.03 | 21 | 26 | 37 | 1 | 12 | 13 | 14 | 15 | 12 | 17 | 84 | |||
| 0.06 | 2 | 2 | 2 | |||||||||||
| IZD (mm) | ||||||||||||||
| 32 | 3 | 3 | 2 | 3 | 5 | 2 | 1 | 5 | 8 | |||||
| 33 | 11 | 12 | 4 | 12 | 15 | 7 | 5 | 3 | 2 | 10 | 27 | |||
| 34 | 31 | 40 | 29 | 50 | 50 | 27 | 8 | 9 | 12 | 2 | 19 | 23 | 100 | |
| 35 | 38 | 51 | 44 | 67 | 66 | 22 | 23 | 13 | 14 | 23 | 16 | 6 | 16 | 133 |
| 36 | 61 | 39 | 60 | 79 | 81 | 2 | 25 | 28 | 25 | 35 | 14 | 25 | 6 | 160 |
| 37 | 15 | 15 | 17 | 26 | 21 | 4 | 3 | 6 | 9 | 25 | 47 | |||
| 38 | 1 | 4 | 3 | 2 | 1 | 4 | 5 | |||||||
| Total | 80/160 | 80/160 | 80/160 | 240 | 240 | 30/60 | 30/60 | 30/60 | 30/60 | 30/60 | 30/60 | 30/60 | 30/60 | 240/480 |
| Mean | 0.02/35.2 | 0.016/35.0 | 0.024/35.4 | 35.2 | 35.1 | 0.013/34.3 | 0.020/35.4 | 0.018/35.3 | 0.020/35.6 | 0.019/35.6 | 0.018/35.2 | 0.021/36.5 | 0.013/34.1 | 0.017/35.2 |
| Median | 0.016/35 | 0.008/35 | 0.016/36 | 35 | 35 | 0.016/34 | 0.016/35 | 0.016/36 | 0.016/36 | 0.02/36 | 0.016/35 | 0.03/36 | 0.016/34 | 0.016/35 |
| Mode | 0.016/36 | 0.008/35 | 0.016/36 | 36 | 36 | 0.016/34 | 0.03/36 | 0.03/36 | 0.03/36 | 0.03/36 | 0.016, 0.03/34 | 0.03/36, 37 | 0.016/34 | 0.016/36 |
| Geometric mean | 0.019/35.2 | 0.012/35.0 | 0.022/35.4 | 35.2 | 35.1 | 0.013/34.2 | 0.020/35.4 | 0.017/35.3 | 0.020/35.3 | 0.019/35.5 | 0.018/35.1 | 0.021/36.4 | 0.014/34.1 | 0.017/35.2 |
| Range | 2/7 | 3/6 | 3/7 | 7 | 7 | 3/5 | 4/4 | 3/7 | 3/5 | 3/3 | 3/5 | 3/4 | 2/5 | 4/7 |
Values in bold are results from the broth microdilution MIC assay. Enmetazobactam was included in the combination at a fixed concentration of 8 μg/ml.
The medium used for broth microdilution MIC determinations was cation-adjusted Mueller-Hinton broth from (A) Difco (lot number 5181782), (B) BD (lot number 5257869), and (C) Oxoid (lot number 1433705). The medium used in the disk diffusion assay was Mueller-Hinton agar from (A) Remel (lot number 348358), (B) BBL (lot number 8123531), and (C) Hardy Diagnostics (lot number 417498).
The eight qualified participating laboratories are coded A through H. Only three laboratories participated in both broth microdilution MIC and disk diffusion M23 QC studies.