Characterization and virulence factors distribution of blaCTX-M and mcr-1carrying Escherichia coli isolates from bovine mastitis.

Abstract

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. 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. 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. High level of association was observed between ESBL-producing and COL-resistance in E. coli of bovine mastitis. 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.