ResistEpist · Dissection of the mechanisms causing the epistasis between antibiotic resistance mutations in Escherichia coli

Dissection of the mechanisms causing the epistasis between antibiotic resistance mutations in Escherichia coli

Antibiotic resistances allow bacteria to survive in the presence of antibiotics, but often cause a fitness disadvantage (called fitness cost) in the absence of the drug. Thus, the cost is the main biological parameter influencing the fate of resistances upon reducing antibiotic use. Antibiotic resistance mutations often interact with each other in a manner that the fitness cost resulting from combining different mutations in the same bacterium is different than the sum of the individual effects of these mutations. These interactions (called epistasis) often cause a reduction in the fitness cost, favoring their maintenance and dissemination in bacterial populations. Antibiotic resistance is the biggest health challenge in the 21st century, and epistatic interactions play a key role in the spread of resistances. Thus, a better undertanding of the epistasis between antibiotic resistance mutations is of paramount importance for global health. This project aims to determine the molecular mechanisms involved in the interaction (epistasis) between antibiotic resistance mutations. We hypothesize that the fitness cost of resistance mutations is the result of the aggregated effects of diverse phenotypes caused by the interference of these mutations with different cellular functions. Objective 1. To determine the phenotypic effects of resistance mutations. Objective 2. Studying these phenotypic effects in evolved strains carrying compensatory mutations. Objective 3. Integration of the results obtained into general hypotheses to explain the cause/s of the epistases. Test of the elaborated hypotheses. Thus, in this project we are studying the effects of these mutations on phenotypes potentially affecting fitness, such as biosynthetic capacity, genome instability and proteostasis imbalance, in order to determine the causes of the fitness cost of single mutations and understanding the mechanisms causing the epistases between mutations. Importantly, some of the phenotypes that we are studying (e.g. genome instability) have never been associated with the cost of antibiotic resistance mutations; thus this research programme may unveil novel mechanisms involved in the fitness effects caused by resistance mutations. The mentioned phenotypes are being analyzed in single and double mutant ancestral strains and in derivatives that have been evolved in the lab, acquiring compensatory mutations that decrease the fitness cost of the resistance mutations. Determining the phenotypes affected in single or double ancestral strains and compensated in the corresponding evolved bacteria will help to identify the mechanisms underlying the epistasis between resistance mutations.

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