Chromosome-mediated colistin resistance in clinical isolates of Klebsiella pneumoniae and Escherichia coli: mutation analysis in the light of genetic background

Purpose: Colistin resistance mechanisms involving mutations in chromosomal genes associated to LPS modification are not completely understood. Mutations in genes coding for the MgrB regulator frequently accounts for colistin resistance in Klebsiella pneumoniae, whereas mutations in genes coding for PhoPQ and PmrAB are frequent in E. coli. Our aim was to perform a genetic analysis of chromosomal mutations in colistin-resistant clinical isolates of K. pneumoniae and E. coli of different STs. Methods: Isolates were obtained in a three-year period in a University Hospital in Santiago-Chile. Susceptibility to colistin, aminoglycosides, cephalosporins, carbapenems and ciprofloxacin, was determined through broth microdilution. Whole genome sequencing was performed for all isolates and chromosomal gene sequences were compared to sequences of colistin susceptible isolates of the same sequence types.