Vet Med - Czech, 2026, 71(1):18-26 | DOI: 10.17221/38/2025-VETMED

Additive effects of ceftiofur-neomycin combination against multidrug-resistant pathogenic Escherichia coli in a murine infection modelOriginal Paper

K-H Do ORCID...¹, M-G Kim ORCID...¹, D-H Ryu ORCID...¹, H-J Ahn ORCID...¹, S-B Kim ORCID...¹, Y-K Go ORCID...¹, SY Kim ORCID...², S Kim ORCID...¹, S-H Lee ORCID...¹, D-K Kim ORCID...³, Y-E Cho ORCID...⁴, J Kim ORCID...⁵, YK Park ORCID...⁶, K Youn ORCID...⁷, H Oh ORCID...¹, K-W Seo ORCID...¹

¹ College of Veterinary Medicine, Chungbuk National University, Cheongju, Republic of Korea

² Division of Zoonotic and Vector-Borne Diseases Research, Center for Infectious Diseases Research, Korea National Institute of Health, Cheongju, Republic of Korea

³ Korea Zoonosis Research Institute, Jeonbuk National University, Iksan, Republic of Korea

⁴ Department of Food and Nutrition, Kyungkook National University, Andong, Republic of Korea

⁵ School of Integrative Engineering, Chung-Ang University, Seoul, Republic of Korea

⁶ Department of Biomedical Comparative Science, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS, USA

⁷ KHU-KIST Department of Converging Science and Technology, Kyung Hee University, Dongdaemun-gu, Seoul, Republic of Korea

This study aimed to evaluate the therapeutic efficacy of a ceftiofur-neomycin combination against a pathogenic multidrug-resistant Escherichia coli strain, KECS-0513, isolated from pigs, using a combination of genomic, in vitro, and in vivo approaches. The minimum inhibitory concentration, minimum bactericidal concentration, and checkerboard assays were performed. Time–kill assays were used to assess bactericidal activity over time, and a murine intraperitoneal infection model was used to evaluate survival outcomes following treatment with monotherapies or combination regimens. Whole genome sequencing indicated that KECS-0513 harboured multiple resistance genes, including bla_TEM-1B, sul3, aadA12, aad(3)-IVa, aph(3’)-Ia, and aph(4)-Ia. The resistance genes were localised within a mobile, element-rich plasmid. In vitro checkerboard assays revealed an additive interaction between ceftiofur and neomycin (fractional inhibitory concentration index = 1.0), and time–kill experiments demonstrated enhanced and sustained bacterial clearance with combination therapy. In vivo infection studies in mice demonstrated that the dual treatment resulted in a substantially higher survival rate (66.7%) compared to treatment with either agent alone (33.3% for each). These results support the practical application of ceftiofur-neomycin combination therapy for controlling swine-associated multidrug-resistant E. coli while minimising the risk of resistance emergence.

Keywords: aminoglycosides; antimicrobial resistance; beta-lactams; combination therapy; whole-genome sequencing

Received: May 17, 2025; Revised: October 1, 2025; Accepted: October 2, 2025; Prepublished online: January 26, 2026; Published: January 28, 2026  Show citation