TABLE 2.
Antimicrobial activity of MRX-8 and comparator agents tested against Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa isolates
| Species and antimicrobial agent | No. of isolates | MIC findings (mg/L) |
Susceptibility results (%) using: |
|||||||
|---|---|---|---|---|---|---|---|---|---|---|
| CLSI criteriaa |
EUCAST criteriaa |
|||||||||
| MIC50 | MIC90 | MIC range | S | I | R | S | I | R | ||
| Escherichia coli | ||||||||||
| MRX-8 | 261 | 0.12 | 0.25 | 0.03 to 16 | ||||||
| Colistin | 261 | 0.25 | 0.25 | 0.06 to 8 | 99.2 | 0.8 | 99.2 | 0.8 | ||
| Polymyxin B | 261 | 0.25 | 0.5 | 0.12 to 8 | 99.6 | 0.4 | ||||
| Amikacin | 261 | 2 | 8 | 0.5 to 16 | 100.0 | 0.0 | 0.0 | 98.9b | 1.1 | |
| Ceftazidime | 261 | 0.25 | 8 | 0.03 to >32 | 88.1 | 2.7 | 9.2 | 82.8 | 5.4 | 11.9 |
| Ceftazidime-avibactam (fixed at 4 mg/L) | 77 | 0.06 | 0.25 | ≤0.015 to 0.25 | 100.0 | 0.0 | 100.0 | 0.0 | ||
| Ceftriaxone | 261 | ≤0.06 | >8 | ≤0.06 to >8 | 83.5 | 0.0 | 16.5 | 83.5,c 83.5d | 0.0d | 16.5,c 16.5d |
| Gentamicin | 261 | 1 | >16 | ≤0.12 to >16 | 87.0 | 0.4 | 12.6 | 86.6b | 13.4 | |
| Levofloxacin | 260 | ≤0.03 | 16 | ≤0.03 to >16 | 68.8 | 0.8 | 30.4 | 68.8 | 0.8 | 30.4 |
| Meropenem | 261 | 0.015 | 0.03 | 0.008 to 8 | 99.6 | 0.0 | 0.4 | 99.6,c 99.6d | 0.4d | 0.4,c 0.0d |
| Piperacillin-tazobactam (fixed at 4 mg/L) | 261 | 2 | 8 | 1 to >128 | 96.6 | 1.5 | 1.9 | 94.3 | 5.7 | |
| Tigecycline | 261 | 0.12 | 0.25 | ≤0.06 to 1 | 100.0e | 0.0 | 0.0 | 98.9 | 1.1 | |
| Klebsiella pneumoniae | ||||||||||
| MRX-8 | 265 | 0.12 | 0.25 | 0.06 to >32 | ||||||
| Colistin | 265 | 0.12 | 0.25 | 0.12 to >32 | 98.1 | 1.9 | 98.1 | 1.9 | ||
| Polymyxin B | 265 | 0.25 | 0.5 | 0.12 to >32 | 98.1 | 1.9 | ||||
| Amikacin | 265 | 1 | 2 | 0.5 to >32 | 98.9 | 0.0 | 1.1 | 98.5b | 1.5 | |
| Ceftazidime | 265 | 0.25 | 16 | 0.03 to >32 | 88.3 | 1.1 | 10.6 | 87.5 | 0.8 | 11.7 |
| Ceftazidime-avibactam (fixed at 4 mg/L) | 102 | 0.12 | 0.25 | 0.03 to 1 | 100.0 | 0.0 | 100.0 | 0.0 | ||
| Ceftriaxone | 265 | ≤0.06 | >8 | ≤0.06 to >8 | 87.9 | 0.0 | 12.1 | 87.9,c 87.9d | 0.0d | 12.1,c 12.1d |
| Gentamicin | 265 | 0.25 | 0.5 | ≤0.12 to >16 | 94.0 | 0.4 | 5.7 | 94.0b | 6.0 | |
| Levofloxacin | 265 | 0.06 | 1 | ≤0.03 to >16 | 86.0 | 4.2 | 9.8 | 86.0 | 4.2 | 9.8 |
| Meropenem | 265 | 0.03 | 0.03 | 0.015 to >16 | 97.4 | 0.4 | 2.3 | 97.7,c 97.7d | 0.4d | 2.3,c 1.9d |
| Piperacillin-tazobactam (fixed at 4 mg/L) | 265 | 4 | 16 | 0.12 to >128 | 93.6 | 2.3 | 4.2 | 89.4 | 10.6 | |
| Tigecycline | 265 | 0.5 | 1 | ≤0.06 to 8 | 98.1e | 1.5 | 0.4 | |||
| Acinetobacter baumannii | ||||||||||
| MRX-8 | 264 | 0.5 | 1 | 0.03 to >32 | ||||||
| Colistin | 264 | 0.25 | 1 | 0.06 to >32 | 97.7 | 2.3 | 97.7 | 2.3 | ||
| Polymyxin B | 264 | 0.25 | 0.5 | 0.12 to 16 | 98.5 | 1.5 | ||||
| Amikacin | 264 | 4 | >32 | 0.5 to >32 | 83.3 | 1.9 | 14.8 | 79.2b | 20.8 | |
| Ceftazidime | 264 | 8 | >32 | 1 to >32 | 65.2 | 7.2 | 27.7 | |||
| Ceftazidime-avibactam (fixed at 4 mg/L) | 91 | 8 | 32 | 1 to >32 | ||||||
| Ceftriaxone | 224 | >8 | >8 | 4 to >8 | 21.4 | 0.0 | 0.0 | |||
| Gentamicin | 264 | 1 | >16 | ≤0.12 to >16 | 75.4 | 5.7 | 18.9 | 75.4b | 24.6 | |
| Levofloxacin | 264 | 0.25 | >16 | ≤0.015 to >16 | 65.9 | 1.1 | 33.0 | 62.9 | 2.3 | 34.8 |
| Meropenem | 264 | 0.5 | >16 | 0.06 to >16 | 71.2 | 0.8 | 28.0 | 71.2,c 71.2d | 1.1d | 28.8,c 27.7d |
| Piperacillin-tazobactam (fixed at 4 mg/L) | 258 | 8 | >128 | ≤0.06 to >128 | 58.5 | 7.0 | 34.5 | |||
| Tigecycline | 264 | 0.5 | 4 | ≤0.06 to 8 | ||||||
| Pseudomonas aeruginosa | ||||||||||
| MRX-8 | 263 | 0.5 | 1 | 0.06 to 2 | ||||||
| Colistin | 263 | 0.5 | 1 | 0.12 to 2 | 100.0 | 0.0 | 100.0 | 0.0 | ||
| Polymyxin B | 263 | 0.5 | 1 | 0.12 to 2 | 100.0 | 0.0 | ||||
| Amikacin | 263 | 4 | 8 | ≤0.25 to >32 | 96.2 | 1.1 | 2.7 | 96.2b | 3.8 | |
| Ceftazidime | 263 | 2 | 32 | 0.25 to >32 | 82.1 | 4.2 | 13.7 | f | 82.1 | 17.9 |
| Ceftazidime-avibactam (fixed at 4 mg/L) | 92 | 2 | 4 | 0.25 to >32 | 98.9 | 1.1 | 98.9 | 1.1 | ||
| Ceftriaxone | 211 | >8 | >8 | 0.5 to >8 | ||||||
| Gentamicin | 263 | 2 | 8 | ≤0.12 to >16 | 87.8 | 6.5 | 5.7 | |||
| Levofloxacin | 263 | 0.5 | 8 | ≤0.03 to >16 | 68.4 | 11.8 | 19.8 | f | 68.4 | 31.6 |
| Meropenem | 263 | 0.5 | 8 | 0.015 to >16 | 82.5 | 5.7 | 11.8 | 82.5,c 82.5d | 8.7d | 17.5,c 8.7d |
| Piperacillin-tazobactam (fixed at 4 mg/L) | 263 | 4 | 128 | ≤0.06 to >128 | 79.8 | 7.6 | 12.5 | f | 79.8 | 20.2 |
| Tigecycline | 263 | 8 | >8 | 0.25 to >8 | ||||||
b
For infections originating from the urinary tract. For systemic infections, aminoglycosides must be used in combination with other active therapy.
c
Using meningitis breakpoints.
d
Using nonmeningitis breakpoints.
e
Using FDA breakpoints.
f
An arbitrary susceptible breakpoint of ≤0.001 mg/L and/or >50 mm has been published by EUCAST, indicating that susceptible should not be reported for this organism-agent combination and intermediate should be interpreted as susceptible-increased exposure.