Key features of -bearing plasmids from isolated from humans and food.

BACKGROUND

-harboring Enterobacteriaceae are reported worldwide since their first discovery in 2015. However, a limited number of studies are available that compared full-length plasmid sequences of human and animal origins.

METHODS

In this study, -bearing plasmids from seven isolates recovered from patients (n = 3), poultry meat (n = 2) and turkey meat (n = 2) in Switzerland were further analyzed and compared. Isolates were characterized by multilocus sequence typing (MLST). The -bearing plasmids were transferred by transformation into reference strain DH5α and MCR-1-producing transformants were selected on LB-agar supplemented with 2 mg/L colistin. Purified plasmids were then sequenced and compared.

RESULTS

MLST revealed six distinct STs, illustrating the high clonal diversity among positive isolates of different origins. Two different -positive plasmids were identified from a single ST48 human isolate. All other isolates possessed a single harboring plasmid. Transferable IncI2 (size ca. 60-61 kb) and IncX4 (size ca. 33-35 kb) type plasmids each bearing were found associated with human and food isolates. None of the -positive IncI2 and IncX4 plasmids possessed any additional resistance determinants. Surprisingly, all but one of the sequenced -positive plasmids lacked the IS element, which is a key element mediating acquisition of into various plasmid backbones.

CONCLUSIONS

There is strong evidence that the food chain may be an important transmission route for -bearing plasmids. Our data suggest that some "epidemic" plasmids rather than specific clones might be responsible for the spread of the gene along the food chain.