Antimicrobial resistance in Campylobacter fetus : emergence and genomic evolution.

is a pathogen, which is primarily associated with fertility problems in sheep and cattle. In humans, it can cause severe infections that require antimicrobial treatment. However, knowledge on the development of antimicrobial resistance in is limited. Moreover, the lack of epidemiological cut-off values (ECOFFs) and clinical breakpoints for hinders consistent reporting about wild-type and non-wild-type susceptibility. The aim of this study was to determine the phenotypic susceptibility pattern of and to determine the resistome [the collection of all antimicrobial resistance genes (ARGs) and their precursors] to describe the genomic basis of antimicrobial resistance in isolates over time. Whole-genome sequences of 295 . isolates, including isolates that were isolated in the period 1939 till the mid 1940s, before the usage of non-synthetic antimicrobials, were analysed for the presence of resistance markers, and phenotypic antimicrobial susceptibility was obtained for a selection of 47 isolates. subspecies () isolates showed multiple phenotypic antimicrobial resistances compared to subspecies () isolates that were only intrinsic resistant to nalidixic acid and trimethoprim. isolates showed elevated minimal inhibitory concentrations for cefotaxime and cefquinome that were observed in isolates from 1943 onwards, and isolates contained substitutions, which conferred resistance to ciprofloxacin. Resistances to aminoglycosides, tetracycline and phenicols were linked to acquired ARGs on mobile genetic elements. A plasmid-derived (O) gene in a bovine isolate in 1999 was the first mobile genetic element observed, followed by detection of mobile elements containing (O) and (44)- genes, and a plasmid from a single human isolate in 2003, carrying and a chloramphenicol resistance gene (). The presence of ARGs in multiple mobile elements distributed among different lineages highlights the risk for spread and further emergence of AMR in . Surveillance for these resistances requires the establishment of ECOFFs for .