Megan R Caswell, Mallory Wright, Georgina Cox
The substrate specificities and functions of bacterial efflux pumps are difficult to define due to the large number encoded in bacterial genomes, variations in gene expression, and functional redundancies. In this chapter, we describe the use of efflux-deficient Escherichia coli mutants as simplified genetic backgrounds for studying efflux pumps. We present detailed methodologies for introducing individual efflux pump-encoding genes under constitutive promoters, and we discuss how these strains can be used to examine the physicochemical substrate profiles of drug efflux pumps using susceptibility testing and chemical properties analysis.