MCR-1 and MCR-1.5 Producing Escherichia coli Clinical Isolates from Argentina

Abstract

Due to the paucity of remaining antibiotics for treating infections caused by carbapenem-resistant Enterobacteriaceae, polymyxins have become the last resort antibiotics. As a consequence, colistin resistance is increasingly reported worldwide. The aim of this study was to analyze colistin-resistant E. coli clinical isolates, recovered between 2014 and 2016 at the University Hospital of Buenos Aires, Argentina. Nine clinical colistin resistant E. coli isolates were studied. These isolates were recovered from urine samples of 5 inpatients and 4 outpatients. Whole genome sequencing was performed using Illumina technology. Plasmid characterization and mating-out assay was done using E. coli J53 as receptor strain. Antibiotic susceptibility (MIC) of clinical isolates and their transconjugants was determined using broth microdilution method. WGS analysis revealed the presence of mcr-1 gene in six out of the 9 isolates: 4 isolates carried mcr-1 and 2 carried mcr-1.5 alleles. All the clinical isolates had MIC values for colistin in the range of 4-16 mg/L. The three isolates lacking any mcr variant, presented point mutations in the chromosomal pmrA or pmrB genes. The mcr-1 gene were located on plasmids similar to the prototypical Incl2-type (KY471308, pMCR-M15049) differing only by little deletions. Until this date mcr-1.5 allele was reported once in Argentina and in Japan, suggested a transcontinental dissemination of this variant.