Eravacycline monotherapy and combination therapy against KPC-2- and NDM-1-co- producing Klebsiella pneumoniae: in vitro and in vivo activity analysis

Background The emergence of carbapenem-resistant Klebsiella pneumoniae (CRKP) co-producing KPC-2 and NDM-1 (K2N1-CRKP) has intensified a major public health threat and severely limited therapeutic options. Eravacycline, a novel tetracycline, shows potent in vitro activity against carbapenem-resistant Enterobacteriaceae. However, its efficacy and synergistic potential against K2N1-CRKP remain unclear. Methods We analyzed the molecular epidemiology of 42 K2N1-CRKP strains and evaluated their susceptibility to eravacycline. The in vitro and in vivo (using a Galleria mellonella model) synergistic effects of eravacycline combined with other antibiotics were determined. Results All 42 strains belonged to ST11. Among them, 92.8% (39/42) were susceptible to eravacycline (MIC50/90: 1 μg/mL; range: 0.5–2 μg/mL). Two strains (KP17, KP18) were resistant to both eravacycline and polymyxin B. The eravacycline-polymyxin B combination showed synergistic activity against 9.5% (4/42) of isolates, including the two dual-resistant strains. No interaction was observed for eravacycline combined with ceftazidime-avibactam, meropenem, or amikacin. Time-kill assays confirmed the rapid, sustained bactericidal activity of the eravacycline-polymyxin B combination against K2N1-CRKP. In the G. mellonella infection model, this combination provided a significantly superior survival benefit compared to monotherapy. Conclusion Eravacycline demonstrates potent in vitro activity against ST11 K2N1-CRKP. While combinations with ceftazidime-avibactam, amikacin, or meropenem showed only additive effects, eravacycline plus polymyxin B exhibited strong synergistic and bactericidal activity both in vitro and in vivo , even against strains resistant to either agent alone. This regimen represents a promising evidence-based therapeutic option for these formidable infections.