Molecular Epidemiology of Dairy Cattle-Associated Escherichia coli Carrying Genes in Washington State.

An increase in the prevalence of commensal carrying genes among dairy cattle was observed between 2008 and 2012 in Washington State. To study the molecular epidemiology of this change, we selected 126 -positive and 126 -negative isolates for determinations of the multilocus sequence types (MLSTs) and antibiotic resistance phenotypes from obtained during a previous study. For 99 isolates, we also determined the alleles using PCR and sequencing and identified the replicon types of -carrying plasmids. The -negative isolates comprised 76 sequence types (STs) compared with 32 STs in -positive isolates. The -positive isolates formed three MLST clonal complexes, accounting for 83% of these isolates; 52% of -negative isolates clustered into 10 clonal complexes, and the remainder were singletons. Overall, -negative isolates had more diverse genotypes that were distinct to farms, whereas -positive isolates had a clonal population structure and were widely disseminated on farms in both regions included in the study. Plasmid replicon types included IncI1 which predominated, followed by IncFIB and IncFIA/FIB. was the predominant CTX-M gene allele, followed by and There was no significant association between plasmid replicon types and bacterial STs, and neither clonal complexes nor major plasmid groups were associated with two discrete dairy-farming regions of Washington State. Infections caused by extended-spectrum β-lactamase (ESBL)-producing occur globally and present treatment challenges because of their resistance to multiple antimicrobial drugs. Cattle are potential reservoirs of ESBL-producing , and so understanding the causes of successful dissemination of genes in commensal bacteria will inform future approaches for the prevention of antibiotic-resistant pathogen emergence.