Characterization of antibiotic resistance in Escherichia coli isolated from wild reindeer in Norway

Antibiotics revolutionized the medical industry when it was introduced due to its ability to cure infections that previously were difficult to treat. The increased use of antimicrobial agents has increased the selection pressure that selects for resistant bacteria. This has led to higher prevalence of resistant infectious bacteria, especially in clinical environments. Horizontal gene transfer (HGT) has made this possible by mechanisms as conjugation, transduction and transformation. Mobile genetic elements, such as plasmids, integrons and transposons, are important for distribution of the resistance genes. Exchange of mobile genetic elements that contain antimicrobial resistance can contribute to the occurrence of new antimicrobial resistance replicons. Antimicrobial resistant Escherichia coli found in wild reindeer in Norway was examined in this study. The purpose of the study was to investigate the isolates and their resistance genes. Forty-two isolates were included in the study; 27 resistant and 15 nonresistant. Disc dilution and MIC (minimum inhibitory concentration) were used to assess the phenotypic resistance pattern of the isolates. Illumina whole-genome sequencing was used to obtain sequence data, and several online tools were used to investigate the genotypic resistance. Phylogenetic groups were determined by multiplex PCR and MLSTs were determined using MLST-Finder. Conjugation was also tested for through a conjugation test. The results showed that multiple isolates were resistant to more than one antimicrobial agent. Most of the isolates had high MIC-values and about 50 % transferred resistance by conjugation test. Multiple sequences containing resistance genes were similar in construction. A high diversity of the isolates was observed, and E. coli belonging to group A. B1, B2 and D was found. The information obtained in this study showed that there is antimicrobial resistant E. coli in wild reindeer in Norway, containing known resistance genes. Furthermore, the multiresistant replicons and similar sequences discovered in the isolates have previously been identified in isolates obtained from human, bear and bird. This supports the fact that resistance genes are widespread. Antimicrobial resistance is an increasing problem in the world today and more information about the dissemination is much needed. Mapping of the antimicrobial resistance in wild animals can give new insight to the dynamics of dissemination and give a wider understanding of how humans have influenced it. Increased knowledge on susceptibility in nature can contribute to better insights on how we can handle this development.Veterinærinstituttet i Oslo Norges miljø- og biovitenskapelige universitet Folkehelseinstituttet OsloM-BIOTE