Two Novel Mutations Associated with Polymyxin-B Resistance in a Pandemic Lineage of Uropathogenic Escherichia coli of the Sequence Type 69.

Background Uropathogenic Escherichia coli (UPEC) are frequent pathogens worldwide, impacting on the morbidity and economic costs associated with antimicrobial treatment. Objectives We report two novel mutations associated with polymyxin-B resistance in an UPEC isolate collected in 2019. Methods Isolate was submitted to antimicrobial susceptibility testing including broth microdilution for polymyxin B. Whole genome was sequenced and analyzed. Results Polymyxin-B total inhibition occurred at 16 mg/L (resistant). UPEC isolate was assigned to the phylogroup D, serotype O117:H4, and Sequence Type 69. mcr genes were not detected, but two novel mutations in the pmrA/basS (A80S) and pmrB/basR (D149N) genes were identified. Conclusions The occurrence of non-mcr polymyxin resistance in E. coli from extraintestinal infections underscores the need of a continuous surveillance of this evolving pathogen.