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Updated: Nov 22, 2025
Characterization of a Pathogenic Escherichia coli Strain Derived from Oreochromis spp. Farms Using Whole-Genome Sequencing
Published on: December 23, 2022
Characterization and virulence factors distribution of blaCTX-M and mcr-1carrying Escherichia coli isolates from
M Shafiq1, J Huang1, J M Shah1
1MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China.
Aim:
To investigate the occurrence of ESBL and colistin-resistant E. coli and its genotypic characterization and identification of virulence determinants in cases of bovine mastitis in three provinces of China.
Materials And Methods:
Five hundred and thirty-five milk samples presenting mastitis symptoms were screened for the presence of ESBL, colistin-resistant and different virulence genes. Susceptibility testing was identified by the micro-dilution method. Escherichia coli isolates were used to detect ESBL genes (blaCTX-M , blaSHV and blaTEM ) and colistin-resistant genes mcr-(1-9). Multiplex PCR approach was used for the detection of major blaCTX-M groups, different phylogroups and virulence genes. The clonal relationship was then evaluated with MLST, MLSA and PFGE.
Results:
Multi-drug resistance (MDR) was found in more than 85% of ESBL and colistin-resistant E. coli isolates. Genotypic characterization showed a dominance of the blaCTX-M-1 group, and the most prevalent alleles observed were blaCTX-M-28 (38·37%), blaCTX-M-14 (17·44%), blaCTX-M-66 (13·95%) and blaCTX-M-55 (10·46%). The targeted virulence genes were detected in 97·89% of isolates. Sequence types ST58 and ST410 were the most predominant (2/20 = 20%). The majority of the E. coli isolates carrying ESBL and mcr-1 were clonally unrelated.
Conclusion:
High level of association was observed between ESBL-producing and COL-resistance in E. coli of bovine mastitis.
Significance And Impact Of The Study:
To the best of our knowledge, this is the first report which shows the genetic diversity of ESBL and mcr-1, and various virulent features of E. coli strains isolated from bovine clinical mastitis in three different provinces of China. The major carriers of the blaCTX-M-1 and blaCTX-M-9 were blaCTX-M-28 and blaCTX-M-14 alleles respectively. The association of ESBL-producing E. coli with mcr-1 is of particular concern.
