Resistencia a colistina en enterobacterias zoonóticas

Abstract

In Spain, infections caused by antimicrobial-resistant bacteria bring out 30 times more deaths than traffic accidents, and it’s expected that in 2050 it will be the first cause of death worldwide. Last resort antibiotics, such as colistin, are necessary for the treatment. In 2015, a horizontally transferable colistin resistance determinant (mcr-1) appeared. The WHO established colistin as a critical antibiotic of great importance and EMA and AEMPS set guidelines that limit the use of colistin in veterinary medicine. Therefore, the main objective of this thesis is to study the mechanisms of colistin resistance in zoonotic enterobacteria. After analyzing 108 colistin-resistant strains of animal origin (80 E.coli’s strains and 28 S.enterica’s strains); and also, an in vitro model of colistin resistance in E.coli (n=10), we observed that colistin resistance is co-expressed resistance to polymyxin B. In clinical isolates the prevailing mechanism is the mcr-1 gene. In addition, in Escherichia coli we found mcr-3 (in combination with mcr-1) and mcr-4 genes (in combination with mcr-1 or polymorphisms in pmrAB). Escherichia coli and Salmonella enterica clinical isolates with mcr-like determinants presented stable phenotypes, whereas Salmonellas’ with polymorphisms in pmrAB were unstable. When performing the directed mutagenesis experiment, we confirmed that the polymorphisms R81S in pmrA, and L14Q, Q99P and V133F in pmrB confer colistin resistance. On the other hand, one of the mutants selected in vitro, CR4, does not present colistin resistant determinants previously described, although its genomic analysis reveals several polymorphisms that require further studies to be confirmed.