In vitro assessment of eravacycline and polymyxin B combination against carbapenem-resistant Klebsiella pneumoniae.

OBJECTIVE

To evaluate the in vitro antibacterial efficacy of eravacycline (ERV) in combination with polymyxin B (PMB) against carbapenem-resistant Klebsiella pneumoniae (CRKP).

METHODS

A total of 101 CRKP isolates were collected at The First Affiliated Hospital of Fujian Medical University from October 2022 to January 2026, and their antimicrobial susceptibility was determined. Carbapenemase genes were detected by PCR and sequencing. Multilocus sequence typing was performed to assess the genetic relatedness of the isolates. MICs of ERV and PMB were determined by broth microdilution method, and their combination effect was assessed using the checkerboard assays.

RESULTS

Carbapenemase genes were detected in all isolates (predominantly blaKPC-2, n = 54), and MLST analysis identified 17 sequence types (STs), with the ST11 clone predominating (71.3%, n = 72). These strains exhibited resistance to the majority of antibiotics tested. The MIC ranges for ERV and PMB were 0.125-8 µg/mL and 0.0313-32 µg/mL, respectively, with MIC50/MIC90 values of 1/4 µg/mL and 2/16 µg/mL. ERV and PMB showed non-susceptibility/resistance rates of 33.7% and 41.6%, respectively. The ERV/PMB combination showed synergy and additivity in 22.8% and 24.8% of isolates, respectively. Group A (ERV‑NS/PMB‑R) showed a significantly higher synergy rate (84.6%) than the other groups (P < 0.001). Furthermore, the strongest association with synergy/additivity was observed in ST11 KPC-2-producing isolates (P = 0.035).

CONCLUSION

The ERV/PMB combination exhibits potent synergistic and additive antibacterial activity against CRKP, particularly against strains non-susceptible to both agents, and may be especially valuable for infections caused by ST11 KPC-2-producing strains.