ORIGINAL RESEARCH article
Front. Vet. Sci.
Sec. Veterinary Infectious Diseases
Volume 12 - 2025 | doi: 10.3389/fvets.2025.1649876
Diversity and Antibiotic Resistance of Cultivable Bacteria in Bulk Tank Milk from Dairy Farms in Shandong Province, China
Provisionally accepted
Yijian Qi1
Zhiyuan Lu2
Ziru Meng3
Xiaozhou Wang1Huahua Chen1Muzi Li1Chaonan Qu1
Pu Zhang4*
Yongxia Liu2*
Jianzhu Liu1*- 1College of Veterinary Medicine, Shandong Agricultural University, Tai`an, Shandong, China
- 2Shandong Provincial Key Laboratory of Zoonoses, Shandong Agricultural Univer-sity, Tai’an, Shandong, China
- 3College of Life Sciences, Shandong Agricultural University, Tai'an, Shandong, China
- 4The Affiliated Tai’an City Central Hospital of Qingdao University, Tai’an, Shandong, China
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This study systematically analyzed bacterial diversity and antimicrobial resistance (AMR) profiles in cow bulk tank milk from five dairy farms (n=30) in Shandong Province, China. Total bacterial counts ranged from 3.94 to 6.68 log CFU/mL, with significant inter-farm variation (P < 0.05). Among 129 isolates, Acinetobacter dominated at the genus level, while Lactococcus lactis was the most prevalent species.Antimicrobial susceptibility testing (AST) against 10 agents was determined using integrated resistance criteria based on Clinical and Laboratory Standard Institute (CLSI) standards and epidemiological cutoff values (ECOFFs). The results showed the highest resistance rate to sulfadiazine (53.2%) and the lowest resistance rate to levofloxacin (6.0%). Additionally, 23% (20/87) of the isolates were found to be multidrug-resistant, with 14 strains identified as resistant to drugs based on the ECOFFs determination criteria. Nine resistance genes targeting seven antibiotic classes were identified by PCR, with sul1 (70.5%) and ant(4')-Ia (54.3%) demonstrating the highest detection rates. Notably, mcr-1, lnu (B), and blaNDM-1 were absent in all isolates. Regional variations in resistance patterns correlated with farm management practices, underscoring the impact of historical antibiotic use on resistance dissemination. These findings highlight the need for enhanced AMR surveillance in raw milk, improved antibiotic stewardship, and targeted interventions to mitigate public health risks associated with microbial contamination and horizontal gene transfer of resistance determinants. This study provides critical data for regional quality control and AMR risk assessment in dairy production systems.
Keywords: Bacteria Diversity, antibiotic resistance, Bulk tank milk, dairy farm, antibiotic resistance genes
Received: 19 Jun 2025; Accepted: 08 Jul 2025.
Copyright: © 2025 Qi, Lu, Meng, Wang, Chen, Li, Qu, Zhang, Liu and Liu. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence:
Pu Zhang, The Affiliated Tai’an City Central Hospital of Qingdao University, Tai’an, Shandong, China
Yongxia Liu, Shandong Provincial Key Laboratory of Zoonoses, Shandong Agricultural Univer-sity, Tai’an, Shandong, China
Jianzhu Liu, College of Veterinary Medicine, Shandong Agricultural University, Tai`an, Shandong, China
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