Fig. 1

Sample collection and bacterial isolation. A Flow chart showing the study design. B A map of China showing the sample collection regions (marked in red, censor code of this map: GS (2019)1684). In each provinces, the numbers of E. coli isolates (numerator) and samples collected (denominator) as well as the numbers of mcr-positive isolates and colistin-resistant isolates are shown. C Pie chart showing the numbers of E. coli isolates with different molecular and phenotypic characteristics (mcr-positive and colistin-resistant or mcr-positive but colistin-sensitive). D Alignment of amino acid sequences of the protein encoded by mcr-1 in mcr-positive and colistin-resistant isolates (marked as Active-MCR-1) and mcr-positive but colistin-sensitive isolates (marked as Inactive-MCR-1); amino acid sites where mutations occur are marked with red boxes