ena-STUDY-UNIVERSITY OF EXETER-03-08-2018-16:28:39:743-30
Recreation of evolutionary dynamics of Escherichia coli growing in the presence of different erythromycin concentrations during 5 days.
Antibiotic dose responses are used to determine treatments that cure infection and mitigate resistance. Despite an 'inverted-U' dose-response geometry described in the literature whereby slow bacterial adaptation occurs at the highest and lowest dosages with fastest adaptation in between, competing hypotheses claim that both sub- and super-inhibitory dosages hasten resistance. We therefore treated Escherichia coli with the antibiotic erythromycin from zero to high dose to elucidate the genomic and phenotypic basis of the inverted-U and so reconcile different views that relate dose to resistance progression. We observed fastest drug resistance adaptation at the minimal inhibitory concentration (MIC) and genotype-phenotype correlations determined from deep sequencing data reveal the molecular basis of this: simultaneous selection for copy number variation in 3 resistance mechanisms. All drug treatments saw E. coli amplify the antibiotic efflux operon acr at a rate that correlated strongly with population density increases and a second efflux operon, emrE, exhibited an analogous pattern of selection. However, lower dosages led to amplification of drug targets, namely the ribosomal RNA operons and these mechanisms created 3 inverted-U geometries within one evolutionary dataset, one for each mechanism under selection. Importantly, we demonstrate that inverted-U relationships are not a universal feature of dose-resistance relationships: unexpectedly, following an acr knockout, resistance adaptation was fastest for that strain at the very lowest antibiotic dosages.
Antibiotic dose responses are used to determine treatments that cure infection and mitigate resistance. Despite an 'inverted-U' dose-response geometry described in the literature whereby slow bacterial adaptation occurs at the highest and lowest dosages with fastest adaptation in between, competing hypotheses claim that both sub- and super-inhibitory dosages hasten resistance. We therefore treated Escherichia coli with the antibiotic erythromycin from zero to high dose to elucidate the genomic and phenotypic basis of the inverted-U and so reconcile different views that relate dose to resistance progression. We observed fastest drug resistance adaptation at the minimal inhibitory concentration (MIC) and genotype-phenotype correlations determined from deep sequencing data reveal the molecular basis of this: simultaneous selection for copy number variation in 3 resistance mechanisms. All drug treatments saw E. coli amplify the antibiotic efflux operon acr at a rate that correlated strongly with population density increases and a second efflux operon, emrE, exhibited an analogous pattern of selection. However, lower dosages led to amplification of drug targets, namely the ribosomal RNA operons and these mechanisms created 3 inverted-U geometries within one evolutionary dataset, one for each mechanism under selection. Importantly, we demonstrate that inverted-U relationships are not a universal feature of dose-resistance relationships: unexpectedly, following an acr knockout, resistance adaptation was fastest for that strain at the very lowest antibiotic dosages.