Selection for loss of tetracycline resistance by Escherichia coli

Abstract

An improved medium for the direct, positive selection of tetracycline-sensitive clones from a population of tetracycline-resistant strains of Escherichia coli is described. Various genetic techniques have been developed requiring the excision of the tetracyclineresistant transposon TnlO from an insertion site

Isolation and characterization of mutants deleted for the sulA-ompA region of the Escherichia coli K-12 chromosome

“…It should be noted that this method for isolating the sulA-ompA deletions did not yield inversions or other rearrangements. This finding is in contrast to the results obtained when deletions are isolated using the transposable element TnlO [31][32][33].…”

A protein that controls the onset of a Salmonella virulence program

“…Then, the tetRA cassette in the cigR promoter region was replaced by annealed oligonucleotides (14723/ 14724). These oligonucleotides were used to electroporate strain pcigR::tetRA harboring pKD46, and the bacterial suspension was plated on media containing fusaric acid and incubated at 42°C to select against the tetRA genes (Maloy & Nunn, 1981). Plasmids expressing CigR and CigR derivatives were constructed as follows: The cigR gene was amplified using primers 15088/15089 for cigR and 15088/14718 for cigR-FLAG and then introduced between the BamHI and HindIII sites of plasmid pUHE21-2lacI q (Soncini et al, 1995).…”

Expression of the tetA(C) tetracycline efflux pump in Escherichia coli confers osmotic sensitivity

“…The gene encodes a protein that is localized to the inner membrane, and which acts as an e¥ux pump to catalyze the exchange of a monocationic magnesium^tetracycline chelate complex from inside the cell with a proton from outside the cell [3]. When present at high levels, the tetA(C) gene product signi¢cantly alters the structure of the inner membrane and this confers a cellular sensitivity to lipophilic chelating agents such as fusaric acid [4,5] as well as an increased permeability to toxic nickel and cadmium salts and aminoglycoside antibiotics [6,7]. In this report we described the surprising ¢nding that high-level expression of tetA(C) confers an additional phenotype of osmotic sensitivity.…”