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Updated: Oct 11, 2025
Characterization of a Pathogenic Escherichia coli Strain Derived from Oreochromis spp. Farms Using Whole-Genome Sequencing
Published on: December 23, 2022
Molecular characteristics of Escherichia coli from bulk tank milk in Korea
Sunghyun Yoon1,2, Young Ju Lee3
1Division of Microbiology, National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson, AR 72079, USA.
Background:
Escherichia coli, which causes subclinical or clinical mastitis in cattle, is responsible for transmitting antimicrobial resistance via human consumption of raw milk or raw milk products.
Objectives:
The objective of this study was to investigate the molecular characteristics of 183 E. coli from bulk tank milk of five different dairy factories in Korea.
Methods:
The molecular characteristics of E. coli such as serogroup, virulence, antimicrobial resistance, and integron genes were detected using polymerase chain reaction and antimicrobial susceptibility were tested using the disk diffusion test.
Results:
In the distribution of phylogenetic groups, group D was the most prevalent (59.6%) and followed by group B1 (25.1%). The most predominant serogroup was O173 (15.3%), and a total of 46 different serotypes were detected. The virulence gene found most often was fimH (73.2%), and stx1, fimH, incC, fyuA, and iutA genes were significantly higher in isolates of phylogenetic group B1 compared to phylogenetic groups A, B2, and D (p < 0.05). Among 64 E. coli isolates that showed resistance to at least one antimicrobial, the highest resistance rate was observed for tetracyclines (37.5%). All 18 integron-positive E. coli carried the integron class I (int1) gene, and three different gene cassette arrangements, dfrA12+aadA2 (2 isolates), aac(6')-Ib3+aac(6')-Ib-cr+aadA4 (2 isolates), and dfrA17+aadA5 (1 isolate) were detected.
Conclusions:
These data suggest that the E. coli from bulk tank milk can be an indicator for dissemination of antimicrobial resistance and virulence factors via cross-contamination.
Insights
Escherichia coli in bulk tank milk carries antimicrobial resistance and virulence factors. This study highlights its role in potential cross-contamination, emphasizing the need for monitoring in dairy production.
Area of Science:
- Veterinary Microbiology
- Food Safety
- Antimicrobial Resistance
Background:
- Escherichia coli in cattle can cause mastitis and transmit antimicrobial resistance (AMR) through raw milk consumption.
- Monitoring AMR in food-producing animals is crucial for public health.
Purpose of the Study:
- To investigate the molecular characteristics of Escherichia coli isolates from bulk tank milk in Korean dairy factories.
- To identify serogroups, virulence genes, AMR profiles, and integron genes in E. coli.
Main Methods:
- Polymerase chain reaction (PCR) was used to detect specific genes.
- Antimicrobial susceptibility testing was performed using the disk diffusion method.
- Phylogenetic grouping and serotyping were conducted.
Main Results:
- Phylogenetic group D was most prevalent (59.6%), followed by group B1 (25.1%). Serogroup O173 was predominant (15.3%).
- The virulence gene fimH was most common (73.2%). Specific genes (stx1, fimH, incC, fyuA, iutA) were more frequent in phylogenetic group B1.
- Tetracycline resistance was highest (37.5%) among resistant isolates. Integron class I (int1) was detected in all integron-positive isolates, with three distinct gene cassette arrangements found.
Conclusions:
- Escherichia coli in bulk tank milk serves as an indicator for the spread of AMR and virulence factors.
- Findings suggest potential cross-contamination risks within the dairy supply chain.
- This highlights the importance of surveillance for E. coli in milk for food safety.
