TABLE 4.
Inter- and intralaboratory comparisons of cefepime-enmetazobactam MICs (fixed enmetazobactam concentration of 8 μg/ml) and inhibition zone diameters with 30/20-μg disks for E. coli ATCC 13353 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) | ||||||||||||||
| 0.03 | 2 | 1 | 1 | 2 | ||||||||||
| 0.06 | 67 | 66 | 64 | 29 | 24 | 29 | 29 | 30 | 1 | 28 | 28 | 197 | ||
| 0.12 | 1 | 4 | 6 | 6 | 1 | 2 | 2 | 11 | ||||||
| 0.25 | 18 | |||||||||||||
| 0.5 | 11 | |||||||||||||
| IZD (mm) | ||||||||||||||
| 27 | 4 | 6 | 2 | 8 | 10 | |||||||||
| 28 | 14 | 11 | 9 | 2 | 14 | 25 | ||||||||
| 29 | 47 | 46 | 30 | 1 | 11 | 1 | 14 | 11 | 25 | 93 | ||||
| 30 | 70 | 73 | 10 | 17 | 23 | 21 | 27 | 20 | 16 | 9 | 143 | |||
| 31 | 67 | 77 | 9 | 32 | 22 | 21 | 17 | 21 | 18 | 4 | 144 | |||
| 32 | 31 | 23 | 10 | 4 | 13 | 8 | 19 | 54 | ||||||
| 33 | 7 | 4 | 4 | 7 | 11 | |||||||||
| 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 | 0.06/30.4 | 0.06/29.8 | 0.07/30.4 | 30.3 | 30.2 | 0.06/29.3 | 0.07/30.9 | 0.06/30.3 | 0.06/31.0 | 0.06/30.0 | 0.34/30.4 | 0.07/31.3 | 0.07/28.8 | 0.06/30.2 |
| Median | 0.06/31 | 0.06/30 | 0.06/30.5 | 30 | 30 | 0.06/29 | 0.06/31 | 0.06/30 | 0.06/31 | 0.06/30 | 0.25/30 | 0.06/31 | 0.06/29 | 0.06/30 |
| Mode | 0.06/31 | 0.06/29 | 0.06/31 | 30 | 31 | 0.06/29 | 0.06/31 | 0.06/30 | 0.06/30, 31 | 0.06/30 | 0.25/31 | 0.06/32 | 0.06/29 | 0.06/31 |
| Geometric mean | 0.06/30.4 | 0.06/29.8 | 0.06/30.4 | 30.2 | 30.2 | 0.06/29.2 | 0.07/30.8 | 0.06/30.3 | 0.06/31.0 | 0.06/30.0 | 0.31/30.4 | 0.06/31.3 | 0.06/28.8 | 0.06/30.2 |
| Range | 3/7 | 2/6 | 2/7 | 7 | 7 | 2/5 | 2/4 | 2/4 | 2/5 | 1/4 | 4/4 | 2/4 | 2/5 | 3/7 |
Values in bold are results determined from the broth microdilution MIC assay. Enmetazobactam was included in the combination at a fixed concentration of 8 μg/ml. Values in bold italics are MIC results that have been excluded from the analysis as the data set determined in the participating laboratory (F) was deemed to be a statistical outlier.
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.