Genomic Characterization of Intrauterine Pathogenic Escherichia coli from Cows with Metritis

Metritis is a major disease in dairy cows causing animal death, decrease of birth rate, milk production and economic loss. Antibiotic treatment is generally used to treat such disease, but it is associated with a high failure rate (23-35%). The reason of the treatment failure is not clear. Our hypothesis is that pathogens in the uteri carry extended spectrum β-lactamases (ESBLs), which give resistance to ceftiofur, the common antibiotic used to treat the disease. The objective was to investigate the prevalence of ESBLs in cows with metritis and characterize the isolated ESBL carriers. Our study investigated the prevalence of ESBL producing bacteria in uterine samples of cows with metritis (n=24) and Whole Genomic Sequencing of the isolated intrauterine pathogenic E. coli (IUPEC) was conducted by Illumina MiSeq for further genomic characterization. We found that the IUPEC causing metritis had a high prevalence of ESBLs (70.8%), which may explain the failure to the treatment. The pathogenicity of these IUPEC isolates was investigated by invasion assay, minimal inhibitory concentration (MIC) test and antimicrobial susceptibility test. The strains had strong invasion activity in bovine endometrial cell lines. The MIC of cefotaxime against the ESBL carriers were higher than 64 µg/mL. The ESBL positive strains had resistance to at least six antibiotics across multiple drug classes. In addition, these ESBL producing IUPEC had high virulence and multidrug resistance according to bioinformatics, which were similar to the reference human clinical E. coli isolates, indicating the possible transmission to human and leading treatment failure in both human and animals.