Multifaceted aspects of MCR-mediated colistin resistance: Fitness, virulence, environmental reservoirs and genomic insights

To date, eight different mcr-variants have been identified encoding phosphoethanolamine transferases contributing to phosphoethanolamine addition to lipid A and thereby conferring colistin resistance. This novel mechanism of plasmid-mediated colistin resistance provides an efficient way in distributing colistin resistance. This thesis aims to further our understanding of the multifaceted aspects of mcr-like genes using detailed molecular analysis including whole-genome sequencing (WGS) for 17 mcr-positive Klebsiella pneumoniae (MCRPKP) and 219 mcr-positive Escherichia coli (MCRPEC) from Thailand and Vietnam. Fitness is an important factor to predict the spread and development of antibiotic resistance. In chapter 3, the data show that over-producing MCR-1 in E. coli imposes a great fitness loss, observed by slow growth rates, impaired membrane integrity and decreased competitiveness. The fitness burden conferred by mcr-3 seems to be more moderate and mcr-3-positive plasmids are more stable and competitive, than that of mcr-1-carrying plasmids. In addition, I provided evidence that blowflies serve as reservoirs of mcr-genes and 48 mcr-1-positive strains recovered from blowflies have been characterized. In particular, the clonal relationship among 17 MCRPKP strains obtained from blowflies was observed by indistinguishable PFGE patterns and an identical phylogenetic tree. The virulence potential of this MCRPKP clone was measured in the Galleria mellonella model. Furthermore, 219 MCRPEC isolates were characterized using WGS and bioinformatics analysis. WGS analysis shows that MCRPEC isolates are highly diverse, with distinct phylogenetic groups and various accessory genes including heavy-metal/antibiotic resistance determinants, virulence factors and toxin-antitoxin systems. The genetic context analysis on the origin and spread of gene mcr-1 and mcr-3, provides important knowledge of understanding on the movement and dissemination of mcr-like genes bacterial population