Combined effect of eravacycline and omadacycline with other antimicrobial agents against Acinetobacter baumannii

Combined Effect of Eravacycline and Omadacycline with Other Antimicrobial Agents Against Acinetobacter baumannii Objective: This study aims to investigate the in vitro efficacy of eravacycline and omadacycline, third-generation tetracyclines, both alone and in combination with six other antibiotics (ceftazidime, meropenem, amikacin, tobramycin, ciprofloxacin, and colistin), against clinical isolates of Acinetobacter baumannii. Materials and Methods: The minimum inhibitory concentration (MIC) values of eravacycline and omadacycline for 50 A. baumannii strains isolated from clinical specimens at Balıkesir University Hospital were determined by broth microdilution method. Results were interpreted according to EUCAST and CLSI guidelines. In addition, 10 meropenem-resistant strains were selected and combinations of both antibiotics with six other antibiotics were analyzed using the checkerboard method. Results: Among the tested strains, 88% were resistant to meropenem, and 6% were resistant to colistin. The MIC ranges of eravacycline and omadacycline were 0.12–4 µg/mL and 0.5–8 µg/mL, respectively. The MIC50 values for eravacycline and omadacycline were 0.5 µg/mL and 1 µg/mL, respectively, while the MIC90 values for both were 2 µg/mL. Synergy was observed in 80%, 80%, 70%, 60%, and 50% of the strains for eravacycline and in 80%, 70%, 60%, 50%, and 30% of the strains for omadacycline combined with ceftazidime, meropenem, colistin, amikacin, and ciprofloxacin,respectively, Neither antibiotic showed synergy with tobramycin. Conclusion: Eravacycline and omadacycline exhibited low MIC values and high rates of synergy with several antibiotics, suggesting their potential utility against A. baumannii. These in vitro findings highlight the need for further studies to evaluate the clinical efficacy of these agents in treating resistant A. baumannii infections. Keywords: Antibiotic Resistance, Checkerboard, Synergy.