Antimicrobial resistance in E. coli from Swedish calves and the surrounding environment

Sammanfattning: The discovery of the first antibiotic by Alexander Fleming was a major milestone in the history of modern medicine. However, with each new antibiotic class introduced to the market, antimicrobial resistance (AMR) rapidly occurred. AMR is a zoonotic problem and even though many countries worldwide banned the use of antibiotics for animal growth promotion, the amount of antimicrobial use for livestock is still high.In this project the situation of antimicrobial resistance was evaluated at 55 Swedish dairy farms. The MICs for 14 antibiotic classes were analyzed for 481 E.coli isolates from different sample types (calves, manure drainages, manure wells, birds, rodents, flies). 40.7% of all isolates were resistant to at least one of the antibiotic drugs, among which 63.3% were multi-resistant. The antibiotic to which the highest number of strains was resistant to was Streptomycin, an antibiotic that is commonly used for infected cows. Interestingly, strains from one type of host were more resistant to certain antibiotic classes than others. Transmission between all sample types is therefore less likely. However, results from whole-genome-sequencing showed the same MLST types of strains from the same and neighboring farms, demonstrating close relatedness and a possible transmission. Furthermore, high colistin-resistance prevalence occurred (4.1-27.8%), which was not expected as no colistin-resistant strain has been isolated from animals in Sweden so far. Only one ESBL-producing E.coli was found, which goes along with previous studies. Taken together, these findings highlight the importance of understanding the situation of antimicrobial resistance at Swedish dairy farm and give an insight into transmission routes.