Non-ST131 Escherichia coli from cattle harbouring human-like blaCTX-M-15-carrying plasmids

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Abstract

Objectives

To characterize blaCTX-M-15-carrying plasmids and lineages of nine strains of Escherichia coli from cattle.

Methods

Plasmid DNA was analysed using PCR-based replicon typing and plasmid sub-typing schemes, restriction fragment length polymorphism, S1 nuclease-PFGE and Southern hybridization. Strains were characterized by PFGE, multilocus sequence typing, phylogenetic grouping and B2-O25b:H4-ST131 (where ST stands for sequence type) clone screening. Susceptibilities to antimicrobials were determined by agar diffusion and resistance genes were characterized by PCR and sequencing.

Results

The blaCTX-M-15 gene was found on F31:A4:B1/IncFII and F2:A–:B–/IncFII plasmids, which have been reported abundantly in humans. On F31:A4:B1/IncFII plasmids, the blaCTX-M-15 gene was associated with the blaTEM-1, blaOXA-1 and aac(6′)-Ib-cr resistance genes. The blaCTX-M-15 gene was also found on IncI1 plasmids of the CC31 clonal complex, recently identified in the human epidemic and virulent E. coli clone O104:H4. None of the cattle isolates belonged to the human and widespread clone B2-O25b:H4/ST131, but were mostly of new STs and of the phylogenetic groups A (n = 4), B1 (n = 3) or D (n = 2). The E. coli isolates harbouring the blaCTX-M-15-carrying plasmids were genetically diverse, and were recovered from different geographical locations and farms and at different times.

Conclusions

This study demonstrates that blaCTX-M-15-carrying plasmids from cattle-derived non-ST131 E. coli isolates were highly similar to those found in ST131 E. coli isolates commonly reported in humans. It also exemplifies the key role of plasmids versus clonal dissemination in the spread of the blaCTX-M-15 gene among cattle, and possibly between E. coli isolates detected in humans and cattle.

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