Escherichia coli (E. coli) can easily contaminate the bovine mammary gland; hence, monitoring of bulk tank milk (BTM) samples helps detect mastitis. In this study, we investigated the characteristics of E. coli from BTM of a dairy company. A total of 58 BTM batches were collected from 29 dairy farms of a dairy company, and 40 E. coli were tested in this study. E. coli showed the highest resistance to cephalothin (52.4%), followed by colistin (28.6%), ampicillin (19.0%) and tetracycline (19.0%). However, E. coli showed low resistance from 0% to 9.5% against other 14 antimicrobials. In the distribution of antimicrobial resistant gene, β-lactamases genes blaOXA and tetracyclines-resistant gene tetB were detected in 15 (37.5%) and 2 (5.0) isolates, respectively, and blaTEM, aac (6')-Ib, aac (3)-II, tetA, sul1 and sul2 genes were only detected once in each (2.5%) isolate. The O127 (22.5%) serogroup was the most predominant, but all E. coli isolates were divided into 20 serogroups. The occurrence of antimicrobial-resistant bacterial infection can be problematic as it not only deteriorates the milk quality but also limits the therapeutic choices of antimicrobials in humans. Therefore, continuous monitoring is recommended to track antimicrobial-resistant E. coli in BTM and raw milk.

• Mun-Jo Yun(College of Veterinary Medicine & Zoonoses Research Institute, Kyungpook National University/Gyeongsangbuk‐do Provincial Government Office)
• Young Ju Lee(College of Veterinary Medicine & Zoonoses Research Institute, Kyungpook National University) Corresponding Author.