In vitro and in vivo antibacterial activity of oral tebipenem in combination with novel β-lactamase inhibitors (avibactam, relebactam, vaborbactam) against KPC-producing Enterobacterales.

PURPOSE: Carbapenem-resistant Enterobacterales (CRE) pose a severe and growing threat to global public health, with limited clinically available therapeutic options. This study aimed to evaluate the antibacterial efficacy of tebipenem (TEB) combined with the novel β-lactamase inhibitors avibactam, relebactam, and vaborbactam, both in vitro and in vivo, against a panel of 77 clinical isolates of KPC-producing Enterobacterales.

METHODS

The MICs of ceftazidime-avibactam (CAZ-AVI), TEB, TEB-avibactam (TEB-AVI), TEB-relebactam (TEB-REL), and TEB-vaborbactam (TEB-VAB) were determined using the broth microdilution method. Time-kill assays, biofilm formation tests, Galleria mellonella assays, and scanning electron microscopy imaging were employed to assess the antibacterial activity of the combination of TEB and new β-lactamase inhibitors (AVI, REL, and VAB) against KPC-producing Enterobacterales isolates in vitro and in vivo. PCR and Sanger sequencing were used to identify carbapenemase genes.

RESULTS

Antimicrobial susceptibility testing revealed that the majority of isolates exhibited high resistance to TEB, with 90.9% (70/77) exhibiting MIC values of ≥ 64 µg/mL. Among the single KPC-producers (n = 77), the combination of TEB with either avibactam (AVI) or vaborbactam (VAB) significantly reduced the TEB MIC₅₀/MIC₉₀ values from > 64/>64 µg/mL to 1/4 µg/mL, respectively. Notably, the antibacterial efficacy of TEB-AVI combinations was comparable to that of ceftazidime-avibactam (CAZ-AVI), which exhibited MIC₅₀/MIC₉₀ values of 2/4 µg/mL. Similarly, TEB combined with relebactam (REL) led to a significant reduction in TEB MIC₅₀/MIC₉₀ values, decreasing from > 64/>64 µg/mL to 2/4 µg/mL, respectively. Furthermore, the MIC values of TEB-AVI, TEB-REL, and TEB-VAB against the CAZ-AVI-resistant isolate harboring blaKPC-14 were all ≤ 0.25 µg/mL. Time-kill assays further confirmed that TEB combined with these novel β-lactamase inhibitors exerted potent antibacterial effect against KPC-producing Enterobacterales isolates. Compared with TEB monotherapy, the bacteria treated with combinations of TEB and novel β-lactamase inhibitors exhibited a reduction of over 2 log10 CFU/mL within 0-8 h. Scanning electron microscopy and biofilm formation experiments revealed that the combination of TEB and novel β-lactamase inhibitors induced bacterial deformation and swelling, caused significant damage to the cell membrane surface structure, and reduced bacterial density. Additionally, in vivo survival experiments using G. mellonella larvae showed that the combination of TEB and these novel β-lactamase inhibitors significantly improved the 7-day survival rate of infected larvae, with survival exceeding 50% by day 5 post-infection.

CONCLUSION

The combinations of oral TEB and novel β-lactamase inhibitors exhibit a potent antibacterial activity against KPC-producing Enterobacterales isolates in vitro and in vivo. Their potency is comparable to that of CAZ-AVI, and they even demonstrate potential efficacy against CAZ-AVI-resistant isolates. These findings provide a theoretical basis for the clinical management of CRE infections. Additionally, this combination serves as a viable step-down therapeutic option potentially facilitating earlier hospital discharge.