A Single-Cell View of Multiple Antibiotic Resistance in Escherichia coli

By Calin Guet, University of Chicago

Nov 4, 2008

CNLS Conference room.

Multiple antibiotic resistance in pathogenic bacteria is one of the main threats to public health. The multiple antibiotic resistance or mar phenotype involves several transcriptional regulators that together control influx and efflux of toxic chemical from the cell. The molecular biology of the mar phenotype has been studied exclusively at the population level. Single-cell studies of the gene expression dynamics of genes responsible for mar are necessary in order to understand cellular variability in resistance to antibiotics. The mar operon of Escherichia coli is constituted of a repressor marR, and an activator gene marA. MarA governs the expression of the efflux pump AcrAB - TolC, the main determinant of multi drug resistance in Escherichia coli. Using the fluorescent protein Venus-YFP we monitor in real time the activity of the mar promoter in single cells across linear micro-colonies. This approach enables us to construct genealogies of promoter activities across several generations. We determine the activity of the mar promoter for different values of the inducer salicylate. We find that in response to a steady level of inducer, mar promoter activity is widely heterogeneous across genetically identical daughter cells. Different promoter activity levels are maintained and inherited over several generations. We find that heterogeneity in promoter activity varies with inducer level. The heterogeneous promoter activity phenotype is abolished in a strain that is deleted for the repressor MarR. Our single-cell approach reveals the presence of non-genetic inheritance patterns in the activity of the mar promoter.

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