Occurrence and molecular epidemiology of fosA3-bearing Escherichia coli from ducks in Shandong province of China.

The plasmid-borne fosfomycin resistance gene fosA3 has been identified in Escherichia coli (E. coli) from various animals but has rarely been reported in ducks. In this study, we investigated the fosA3 prevalence and molecular characteristics of fosA3-harboring E. coli strains from ducks in Shandong province of China. In 416 E. coli isolates, 91 (21.88%) were identified as fosA3-bearing strains, and the fosfomycin-resistant phenotype of 88 of the 91 fosA3-harboring strains was successfully transferred to the recipient strains. Seven different genetic structures surrounding the fosA3 gene were detected and 2 new contexts were discovered among the fosA3-carrying E. coli. Twenty fosA3-harboring isolates and their trans-conjugants were randomly selected for pulsed-field gel electrophoresis (PFGE) typing and S1-nuclease PFGE, respectively. The PFGE patterns revealed that the 20 randomly selected fosA3-bearing isolates were not a result of clonal dissemination. S1-PFGE showed that 15 of the 20 randomly selected trans-conjugants carried a single plasmid, and these 15 plasmids that harbored fosA3 (55-190 kb) were distributed into the following replicon types: IncF (n = 11), IncI1 (n = 1), IncN (n = 1), untypable (n = 1), and W-FIC (n = 1). Additionally, as vectors for fosA3 in E. coli, F-:A1:B6, N/ST1, IncI1/ST2, W-FIC, and one untypable plasmid had never been reported before. These observations highlighted the importance of ducks as a reservoir for multidrug-resistant fosA3-carrying E. coli.