Showing papers by "Ian Chopra published in 1990"
TL;DR: Growing cultures of Escherichia coli with propionic acid or formic acid at pH 5.0 produced bacteriostasis lasting 30 and 120 min respectively, and growth resumed after continued incubation in the presence of acid, but cells from acid-treated cultures were larger than controls.
Abstract: Incubating cultures of Escherichia coli with propionic acid (5 mmol/l) or formic acid (10 mmol/l) at pH 5.0 produced bacteriostasis lasting 30 and 120 min respectively. During this time rates of RNA, DNA, protein, lipid and cell wall synthesis were reduced. Growth resumed after continued incubation in the presence of acid, but cells from acid-treated cultures were larger than controls. DNA synthesis was particularly sensitive to the presence of the propionic or formic acid.
173 citations
TL;DR: A sensitive microbiological detection system for tetracyclines, utilizing an Escherichia coli strain containing a cloned tetA-lacZ gene fusion, is described, with a 12-fold induction of beta-galactosidase synthesis.
Abstract: A sensitive microbiological detection system for tetracyclines, utilizing an Escherichia coli strain containing a cloned tetA-lacZ gene fusion, is described. Expression of beta-galactosidase by the fusion plasmid pUB3610 remained subject to regulatory control by the TetR repressor protein, with the presence of tetracyclines in the growth medium leading to a 12-fold induction of beta-galactosidase synthesis. Because synthesis of beta-galactosidase was influenced to a small extent by the carbon source and the addition of cyclic AMP to the medium, cells were grown in the presence of cyclic AMP to enhance the sensitivity of the assay. All commonly marketed tetracyclines and some derivatives at concentrations as low as 0.1 ng/ml could be detected in the growth medium. A plate assay utilizing the fusion plasmid that detects 1 ng of tetracycline has also been developed.
26 citations
TL;DR: Induction of the cloned ampC Citrobacter freundii beta-lactamase in Escherichia coli by 6-aminopenicillanic acid was prevented by periplasmic TEM beta-mase in the same cell, which implies that entry of the beta- lactam into the cytoplasm is not necessary for induction of ampC.
Abstract: Induction of the cloned ampC Citrobacter freundii beta-lactamase in Escherichia coli by 6-aminopenicillanic acid was prevented by periplasmic TEM beta-lactamase in the same cell. In contrast, cytoplasmic TEM beta-lactamase did not prevent induction. This result implies that entry of the beta-lactam into the cytoplasm is not necessary for induction of ampC.
7 citations