Colistin-resistant Escherichia coli belonging to different sequence types: genetic characterization of isolates responsible for colonization, community- and healthcare-acquired infections

The plasmid-mediated colistin-resistance gene named mcr-1 has been recently described in different countries and it became a public health challenge. Of note, few studies have addressed the spread of Escherichia coli harboring the mcr-1 gene in both, community and hospital settings. A total of seven colistin-resistant E. coli carrying mcr-1, collected from 2016 to 2018, from community (n=4), healthcare-acquired infections (n=2) and colonization (n=1) were identified in three high complexity hospitals in Sao Paulo, Brazil. These colistin-resistant isolates were screened for mcr genes by PCR and all strains were submitted to Whole Genome Sequencing and the conjugation experiment. The seven strains belonged to seven distinct sequence types (ST744, ST131, ST69, ST48, ST354, ST57, ST10), and they differ regarding the resistance profiles. Transference of mcr-1 by conjugation to E. coli strain C600 was possible in five of the seven isolates. The mcr-1 gene was found in plasmid types IncX4 or IncI2. Three of the isolates have ESBL-encoding genes (blaCTX-M-2, n=2; blaCTX-M-8, n=1). We hereby report genetically distinct E. coli isolates, belonging to seven STs, harboring the mcr-1 gene, associated to community and healthcare-acquired infections, and colonization in patients from three hospitals in Sao Paulo. These findings point out for the potential spread of plasmid-mediated colistin-resistance mechanism in E. coli strains in Brazil.