Genome sequences of antibiotic-resistant Escherichia coli isolated from veal calves in the USA

Objectives: The aim of this study was to describe the genome sequences of 38 antibiotic-resistant Escherichia coli isolated from veal calves.

Methods: The isolates were recovered in 2015 from nine veal farms in the eastern USA and were screened for antibiotic susceptibility using an automated microdilution procedure. The draft genomes were sequenced on an Illumina NextSeq 500 platform and were assembled using SPAdes.

Results: In total, 294 resistance genes, categorised into 42 unique genes, conferring resistance to seven different antibiotic classes were detected. Extended-spectrum β-lactamase (ESBL) genes (bla_CTX-M and bla_CMY) and the azithromycin resistance gene mph(A) were detected in multiple genomes. Furthermore, mutations in gyrA, parC and parE conferring resistance to fluoroquinolones were detected, as were mutations in the ampC promoter responsible for hyperproduction of β-lactamases. We identified 25 unique sequence types (STs), including STs that are associated with extraintestinal infections.

Conclusion: The results of this study indicate a high level of diversity among multidrug-resistant E. coli isolates from veal operations. The identification of multiple isolates encoding resistance to β-lactams, macrolides and fluoroquinolones as well as virulence factors responsible for human infections warrants more study on the ecology of antibiotic resistance in veal operations.