Abstract
Background
Eravacycline (ERV is the first fully synthetic fluorocycline with activity against tetracycline (TET)-resistant organisms. In addition, it is 2–8 times more potent than tigecycline (TGC). Like other tetracyclines, it inhibits protein synthesis by binding to the 30S ribosomal subunit exhibiting a broad spectrum of activity. To further explore its activity, we tested 143 clinical isolates of Bacteroides and included TET, TGC and other drugs frequently used to treat serious infections.
Methods
Clinical isolates recovered during the past 3 years from patients in southern California were saved as pure cultures in 20% skim milk at −70°C. Prior to testing, they were transferred at least twice to ensure purity and good growth. Antimicrobials included ERV, TET, TGC, piperacillin-tazobactam (P-T), meropenem (MER), clindamycin (CLI), and metronidazole (MET). The method was agar dilution as described in the CLSI M11-A8 document for testing anaerobes using Brucella agar and incubation in the anaerobic chamber at 36°C for 44h. The MIC was defined as the lowest dilution that completely inhibited growth or resulted in a marked reduction compared with a drug-free growth control.
Results
The MIC90 values (µg/ml) for Bacteroides and Parabacteroides are presented in the table:
| Organism (no.) | ERV | TGC | TET | P-T | MER | CLI | MET |
|---|---|---|---|---|---|---|---|
| B. caccae (10) | 2 | 16 | >32 | 8 | 0.25 | >32 | 1 |
| B. fragilis (25) | 2 | 8 | >32 | 1 | 0.5 | >32 | 1 |
| B. theta (25) | 4 | 16 | >32 | 16 | 1 | >32 | 1 |
| B. ovatus (33) | 4 | 32 | >32 | 8 | 4 | >32 | 2 |
| B. vulgatus (25) | 1 | 4 | >32 | 8 | 1 | >32 | 2 |
| P. distasonis (25) | 1 | 8 | >32 | 8 | 1 | >32 | 2 |
ERV showed excellent activity against these strains and was 4–8 times more potent than TGC. TET and CLI were poorly active with most strains showing marked resistance. The other antimicrobials showed modest to good activity.
Conclusion
This study confirmed the improved activity of ERV over TGC against Bacteroides and suggests that ERV may be an appropriate choice for infections involving these organisms.
Disclosures
E. Goldstein, Tetraphase Pharmaceuticals: Research Contractor, Research grant