Infection and Drug Resistance (Sep 2023)
Chromosome-Mediated Colistin Resistance in Clinical Isolates of Klebsiella pneumoniae and Escherichia coli: Mutation Analysis in the Light of Genetic Background
Abstract
María Paz Riquelme,1 Rodrigo W Martinez,2,3 Bárbara Brito,4 Patricia García,1,3,5 Paulette Legarraga,1,5 Aniela Wozniak1,3,5 1Department of Clinical Laboratories - School of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile; 2Genomics & Resistant Microbes Group (Germ) - Instituto de Ciencias e Innovación en Medicina (ICIM); School of Medicine-Clínica Alemana, Universidad del Desarrollo, Santiago, Chile; 3Millennium Nucleus for Collaborative Research on Bacterial Resistance (MICROB-R), Santiago Chile; 4Australian Institute for Microbiology & Infection - Faculty of Science, University of Technology Sydney, Sydney, Australia; 5Clinical Laboratories Network, Red de Salud UC-CHRISTUS, Santiago, ChileCorrespondence: Aniela Wozniak, Laboratory of Microbiology, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4686, 3rd Floor, Santiago, 7820436, Chile, Tel +562-23548573, Fax +562-23548571, Email [email protected]; [email protected]: Colistin resistance mechanisms involving mutations in chromosomal genes associated with LPS modification are not completely understood. Mutations in genes coding for the MgrB regulator frequently account 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 (MIC ≥ 4 μg/mL) clinical isolates of K. pneumoniae (n = 8) and E. coli (n = 7) of different STs.Methods: Isolates were obtained in a 3-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 with sequences of colistin-susceptible isolates of the same sequence types.Results: None of the isolates carried mcr genes. Most of the isolates were susceptible to all the antibiotics analyzed. E. coli isolates were ST69, ST127, ST59, ST131 and ST14, and K. pneumoniae isolates were ST454, ST45, ST6293, ST380 and ST25. All the isolates had mutations in chromosomal genes analyzed. K. pneumoniae had mutations mainly in mgrB gene, whereas E. coli had mutations in pmrA, pmrB and pmrE genes. Most of the amino acid changes in LPS-modifying enzymes of colistin-resistant isolates were found in colistin-susceptible isolates of the same and/or different ST. Eleven of them were found only in colistin-resistant isolates.Conclusion: Colistin resistance mechanisms depend on genetic background, and are due to chromosomal mutations, which implies a lower risk of transmission than plasmid-mediated genes. Colistin resistance is not associated with multidrug-resistance, nor to high-risk sequence types.Keywords: sequence type, LPS-modifying enzymes, polymorphism vs potential mutation, MgrB regulator, PmrA-PmrB and PhoP-PhoQ three-component systems
