In vitro Screening for Synergistic Polymyxin B-Based Combinations Against KPC- Producing Carbapenem-Resistant Klebsiella pneumoniae

Menghan Lv,1,* Hanxi Yi,2,* Yalan Liu,1 Yehua Xie,3 Zeneng Cheng,1 Feifan Xie,1 Sanwang Li4,5 1Division of Biopharmaceutics and Pharmacokinetics, Xiangya School of Pharmaceutical Sciences, Central South University, Changsha, People’s Republic of China; 2Department of Pathology, School of Basic Medical Science, Central South University, Changsha, People’s Republic of China; 3Certara (Shanghai) Pharmaceutical Consulting Co., Ltd, Shanghai, People’s Republic of China; 4Department of Pharmacy, The Second Xiangya Hospital, Central South University, Changsha, People’s Republic of China; 5Institute of Clinical Pharmacy, Central South University, Changsha, People’s Republic of China*These authors contributed equally to this workCorrespondence: Feifan Xie, Division of Biopharmaceutics and Pharmacokinetics, Xiangya School of Pharmaceutical Sciences, Central South University, Tongzipo Road 172, Changsha, 410013, People’s Republic of China, Tel +86 0731 8265 0451, Email [email protected] Sanwang Li, Department of Pharmacy, The Second Xiangya Hospital, Central South University, Middle Renmin Road 139, Changsha, 410011, People’s Republic of China, Tel +86 0731 8529 2099, Email [email protected]: Carbapenem-resistant Klebsiella pneumoniae (CRKP) infections often necessitate combination therapy, yet effective treatment options remain limited. This study aimed to evaluate the bactericidal effects of polymyxin B–based combination therapy with ten representative antibiotics against KPC-producing CRKP.Methods: Phenotypic and genotypic analyses were performed on clinically CRKP isolates. Susceptibility of KPC-producing strains was assessed via broth microdilution. Ten heterogeneous isolates were selected for 24-hour static time-kill assays to evaluate the bactericidal activity of polymyxin B and ten antibiotics (tigecycline, minocycline, meropenem, imipenem, doripenem, amikacin, fosfomycin, aztreonam, ceftazidime, and cefepime)—both as monotherapies and in combination with polymyxin B. Additionally, 24-hour time-course kill studies were conducted for a representative polymyxin B–based combination against a polymyxin B–resistant strain using clinically relevant concentration matrices.Results: Among 22 CRKP isolates, 16 consistently produced KPC enzymes and carried the blaKPC-2 gene. Of the 10 selected KPC-producing strains, polymyxin B susceptibility was classified as 2 susceptible, 4 intermediate, and 4 resistant. All monotherapies, including polymyxin B, showed limited efficacy. Notable synergistic activity was observed when polymyxin B was combined with tigecycline (8/10), imipenem (7/10), ceftazidime (9/10), or cefepime (9/10), while other combinations were largely ineffective. A 24-hour time-course kill assay using polymyxin B plus ceftazidime as a representative demonstrated that synergy was concentration-dependent and could be rapidly achieved at clinical concentration combinations.Conclusion: This study demonstrated that combinations of polymyxin B with tigecycline, imipenem, ceftazidime, or cefepime show promising therapeutic potential against KPC-producing CRKP. Further studies are warranted to evaluate their in vivo efficacy. Keywords: carbapenem-resistant Klebsiella pneumoniae, time-kill assay, polymyxin B, combination therapy