TABLE 1.
Comparison of MIC values for isolates of E. coli, S. aureus, and E. faecalis using fresh versus aged CA-MHB
| Organism and drug | No.a | Result for aged vs fresh medium: |
Essential agreementb | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Log2 difference |
% log2 difference |
|||||||||||||||
| ≥−3 | −2 | −1 | 0 | +1 | +2 | ≥+3 | ≥−3 | −2 | −1 | 0 | +1 | +2 | ≥+3 | |||
| Overall | ||||||||||||||||
| Eravacycline | 39 | 3 | 22 | 11 | 1 | 2 | 7.7 | 56.4 | 28.2 | 2.6 | 5.1 | 92.3 | ||||
| Tetracycline | 29 | 5 | 23 | 1 | 17.2 | 79.3 | 3.4 | 100.0 | ||||||||
| Tigecycline | 39 | 2 | 25 | 10 | 2 | 5.1 | 64.1 | 25.6 | 5.1 | 69.2 | ||||||
| E. coli | ||||||||||||||||
| Eravacycline | 13 | 1 | 8 | 4 | 7.7 | 61.5 | 30.8 | 100.0 | ||||||||
| Tetracycline | 7c | 1 | 5 | 1 | 14.3 | 71.4 | 14.3 | 100.0 | ||||||||
| Tigecycline | 13 | 1 | 9 | 3 | 7.7 | 69.2 | 23.1 | 76.9 | ||||||||
| S. aureus | ||||||||||||||||
| Eravacycline | 13 | 1 | 9 | 2 | 1 | 7.7 | 69.2 | 15.4 | 7.7 | 92.3 | ||||||
| Tetracycline | 13 | 3 | 10 | 23.1 | 76.9 | 100.0 | ||||||||||
| Tigecycline | 13 | 1 | 12 | 7.7 | 92.3 | 100.0 | ||||||||||
| E. faecalis | ||||||||||||||||
| Eravacycline | 13 | 1 | 5 | 5 | 2d | 7.7 | 38.5 | 38.5 | 15.4 | 84.6 | ||||||
| Tetracycline | 9e | 1 | 8 | 11.1 | 88.9 | 100.0 | ||||||||||
| Tigecycline | 13 | 4 | 7 | 2 | 30.8 | 53.8 | 15.4 | 30.8 | ||||||||
Number of isolates with defined MIC values available for analysis.
Essential agreement is defined as MIC values at or within one doubling dilution of standard (fresh).
Six isolates were highly tetracycline resistant (MIC of >32 μg/ml) and excluded from the analysis as a log2 fold difference in MIC could not be determined.
Results for two E. faecalis isolates with ≥+3 log2 difference for eravacycline were found to be aberrant. Retesting of these isolates in fresh and aged MHB, respectively, showed fresh/aged MIC values (in μg/ml) of 0.008/0.008 and 0.008/0.016 for eravacycline, 0.03/0.25 and 0.06/0.25 for tigecycline, and 1/1 and >32/>32 for tetracycline. Taking the retest data for all three antibiotics into consideration, essential agreements for eravacycline, tetracycline, and tigecycline were 100%, 100%, and 30.8%, respectively.
Four isolates were highly tetracycline resistant (MIC of >32 μg/ml) and excluded from the analysis as a log2 fold difference in MIC could not be determined.