The effect of ampicillin on the electrophysical properties of Escherichia coli cells

The study of the effect of ampicillin on the electrophysical properties of Escherichia coli cells showed that this antibiotic influences the orientational spectra (OSs) of the ampicillin-susceptible E. coli strains K-12 and XL-1 within the frequency range 10–1000 kHz of the orienting electric field and does not affect the OSs of the ampicillin-resistant strains K-12(pUC-18) and XL-1(pHEN1). The change in the electrooptical signal of the ampicillin-susceptible cells was maximum at an ampicillin concentration of 50 µg/ml and did not depend on the exposure time. The conclusion is drawn that changes in the OSs of cells can be used to evaluate their resistance to ampicillin.Translated from Mikrobiologiya, Vol. 74, No. 1, 2005, pp. 126–131.Original Russian Text Copyright © 2005 by Guliy, Markina, Ignatov, Shchegolev, Zaitseva, Bunin, Ignatov.     

Effects of subinhibitory concentrations of nitroxoline on the surface properties of Escherichia coli

Nitroxoline (5-nitro-8-quinolinol; NIQ) at subinhibitory concentrations (sub-MIC) decreased the adherence of uropathogenicEscherichia coli to catheter surface and significantly enhanced cell surface hydrophobicity. The surface hydrophobicity increased in the presence of sub-MIC of NIQ and also in an excess of Mg²⁺. The effect of NIQ on the cell surface was not related to the bacteriostatic effect of this agent. The increase in nitrogen and decrease in phosphate content in the cell surface was found in the presence of NIQ. NIQ did not inhibit the expression of fimbriae.     

The effect of ampicillin on the electrophysical properties of Escherichia coli cells

The study of the effect of ampicillin on the electrophysical properties of Escherichia coli cells showed that this antibiotic influences the orientational spectra (OS) of the ampicillin-susceptible E. coli strains K-12 and XL-1 within the frequency range 10-1000 kHz of the orienting electric field and does not affect the OS of the ampicillin-resistant strains K-12(pUC-18) and XL-1(pHEN1). The change in the electrooptical signal of the ampicillin-susceptible cells was maximum at an ampicillin concentration of 50 microg/ml and did not depend on the exposure time. The conclusion is drawn that changes in the OS of cells can be used to evaluate their resistance to ampicillin.     

Effects of post-induction feed strategies on secretory production of recombinant streptokinase in Escherichia coli

The effects of post-induction nutrient feed rates, on recombinant streptokinase production in fed-batch processes, were investigated using various feed profiles. Recombinant streptokinase was produced using a secretory expression system and was induced by a temperature up-shift, using a temperature-sensitive λ_PL promoter. The specific growth rates decreased sharply upon induction of recombinant protein expression, thus necessitating a variable feed strategy in the post-induction phase. The various feed profiles employed in the post-induction phase included constant feed rates, linearly increasing feed rate and exponentially varying feed rates. Significant differences were obtained in the specific activity of streptokinase produced in these fed-batch processes. A maximum activity per unit biomass of 4.96 × 10⁶ and 4.43 × 10⁶ IU/g DCW was achieved for exponentially decreasing feed and linearly increasing feed, respectively. The decrease in specific growth rate during the post-induction phase was also less pronounced in these cases in comparison to other fed-batch experiments. It was observed that streptokinase productivity is governed by the nutrient feed rate per unit biomass at a critical juncture after induction. The highest activity per unit biomass was obtained when the nutrient feed rate per unit biomass was around 0.7–0.8 g glucose (g DCW)⁻¹ h⁻¹, between 2 and 4 h after induction.     

Escherichia coli O157 can grow in natural freshwater at low carbon concentrations

Whereas much information on the die-off of Escherichia coli in the aquatic environment is available, only few data support its growth under such conditions. We therefore investigated batch growth in microcosms containing different types of sterile freshwater. The water samples were inoculated with low starting cell concentrations of E. coli O157 (3 × 10³ cells ml⁻¹) and growth was followed using nucleic acid staining combined with flow cytometry. We demonstrated that E. coli O157 is able to grow in sterile freshwater at low carbon concentrations, which is against the common view that cell numbers decline over time when added to freshwater samples. A correlation between apparent assimilable organic carbon (AOC_app) concentration and the final cell concentration reached by E. coli O157 was established ( P  <  0.01). A considerable fraction of the AOC_app (34 ± 13%) was used by E. coli O157 but the numerical cell yield was about five-times lower in comparison with the bacterial AOC-test community, which originated from natural freshwater. On average, the maximum specific growth rate ( μ _max) of E. coli O157 growing in sterile freshwater at 30°C was 0.19 ± 0.07 h⁻¹. Batch growth assays at five different temperatures revealed a positive influence of temperature on μ _max of E. coli O157. The results give new information on the behaviour of this common pathogen in the aquatic environment and contribute to microbial risk assessment in order to prevent spreading of water-borne diseases.     

Minimum inhibitory concentrations of intestinal Escherichia coli from broiler chickens after oral administration of apramycin

This study describes the influence of apramycin on minimum inhibitory concentrations (MIC) of intestinal Escherichia coli in young broiler chickens, after oral administration of the antibiotic at a dosage equivalent to a prophylactic course of treatment for 10 d. The bacteria were isolated from cloacal swabs and caecal contents. MICs were determined by agar dilution procedures. MIC of apramycin for the investigated strains ranged from 1 μg ml^-1 to 16 μg ml^-1. Strains obtained from undosed birds mainly had MIC values of 1 μg ml^-1. MIC values of 8 μg ml^-1 or more were recorded only among isolates obtained from chickens which had received apramycin. Administration of apramycin resulted in a slight but statistically significant increase in the average MIC. Statistically higher average MICs were recorded among isolates from cloacal swabs 10 d after withdrawal until the end of the experiment. For strains from caecal contents, this was demonstrated only on one sampling occasion, 15 d after withdrawal.     

Morphological changes in Escherichia coli cells exposed to low or high concentrations of hydrogen peroxide

Escherichia coli cells challenged with low or high concentrations of hydrogen peroxide are killed via two different mechanisms and respond with morphological changes which are also dependent on the extracellular concentration of the oxidant. Treatment with low concentrations (less than 2.5 mM) of H2O2 is followed by an extensive cell filamentation which is dependent on the level of H2O2 or the time of exposure. In particular, addition of 1.75 mM H2O2 results in a growth lag of approximately 90 min followed by partial increase in optical density, which was mainly due to the onset of the filamentous response. In fact, microscopic analysis of the samples obtained from cultures incubated with the oxidant for various time intervals has revealed that this change in morphology becomes apparent after 90 min of exposure to H2O2 and that the length of the filaments gradually increases following longer time intervals. Analysis of the ability of these cells to form colonies has indicated a loss in viability in the first 90 min of exposure followed by a gradual recovery in the number of cells capable of forming colonies. Measurement of lactate dehydrogenase in culture medium (as a marker for membrane damage) has revealed that a small amount of this enzyme was released from the cells at early times (less than 150 min) but not after longer incubation periods (300 min). Cells exposed to high concentrations of H2O2 (greater than 10 mM) do not filament and their loss of viability is associated with a marked reduction in cell volume. In fact, treatment with 17.5 mM H2O2 resulted in a time-dependent decrease of the optical density, clonogenicity, and cellular volume. In addition, these effects were paralleled by a significant release in the culture medium of lactate dehydrogenase thus suggesting that the reduced cell volume may be dependent on membrane damage followed by loss of intracellular material. This hypothesis is supported by preliminary results obtained in electron microscopy studies. In conclusion, this study further demonstrates that the response of E. coli to hydrogen peroxide is highly dependent on the concentration of H2O2 and further stresses the point that low or high concentrations of the oxidant result in the production of different species leading to cell death via two different mechanisms and/or capable of specifically affecting the cell shape.     

Simple medium that preserves low concentrations of Escherichia coli for use in the water bacteriology proficiency test

A medium containing (per liter) 6.8 g of sodium acetate trihydrate, 3.4 g of potassium dihydrogen phosphate, and 0.1 g of magnesium sulfate heptahydrate (medium pH, 5.85 plus/minus 0.05) was developed for use in a water bacteriology proficiency test. The medium maintained 80 to 100 % viability of inoculated Escherichia coli at temperatures up to 31 degrees C for at least 12 days, while the concentrations of bacteria in the medium were as low as 20 bacteria per 100 ml. The medium remained stable after a year of storage. It has been used successfully to preserve bacteria in nine statewide bacteriology proficiency tests for potable and nonpotable water and has also been used in a nationwide pilot test. This report presents the results of these tests.     

Influence of intestinal myoelectrical activity on the growth of Escherichia coli

Intestinal bacteria, particularly those adhering to intestinal epithelial cells, are exposed to electric fields and currents generated by the muscular activity of the small intestine. This activity displays a regular pattern known as the myoelectrical migrating complex (MMC). In order to explore the possibility that these endogenous electric fields could affect bacterial growth, a digitised duodenal signal obtained via serosal electrodes from a healthy calf was recorded and then applied via platinum electrodes to Escherichia coli cultures. The culture tubes were placed within a Faraday shield, incubated at 37 degrees C with shaking, and stimulated by the electric current for 5 or 8 h. The growth of E. coli stimulated by the electric current was significantly altered compared to those of non-stimulated controls: after a period of intensive growth, inhibition of cell division was observed. This was not the case when the bacteria with lon mutation were used. Moreover, synchronic bacterial culture could not be achieved in the presence of the MMC-related electric field. These results suggest that the myoelectrical activity of the duodenum, through action on cell membrane, can affect cell division of intestinal bacteria.     

Effects of toluene on Escherichia coli

Jackson, Robert W. (University of California, San Diego, La Jolla), and J. A. DeMoss. Effects of toluene on Escherichia coli. J. Bacteriol. 90:1420-1425. 1965.-When toluene is added at appropriate levels to exponentially growing cultures of Escherichia coli, a time-dependent loss of turbidity is observed which is concurrent with a loss of material to the medium and with unmasking of beta-galactosidase. In addition, the galactoside permease system is totally destroyed. Electron micrographs confirm the indications that the cells are not being lysed by toluene, although the cytoplasm collapses to the interior of the cell. Included in the material lost from the cell after toluene treatment is 85% of the total ribonucleic acid (RNA), the principal source of which appears to be the ribosomes. The loss of RNA is temperature-dependent. Protein is also lost to the medium as a function of both temperature and available toluene. Up to 25% of the total protein is found in the medium, the precise amount depending on the level of toluene employed. Zone centrifugation studies of extracts from treated cells indicate that toluene elicits a rapid disaggregation of ribosomes that is terminated, at any stage, by disruption of the cells. The disaggregation is temperature-dependent and does not occur at 4 C. It appears to be distinct from the actual degradation of ribosomal RNA and is accompanied by an accumulation of small particles during the initial phases of treatment at 21 C. Toluene added to crude extracts of normal E. coli cells is unable to cause detectable ribosome destruction.     

Translocation of ampicillin transposon Tn1 in Escherichia coli cells during sexual reproduction

The efficiency of Tn1 transposition has been shown to increase considerably in course of bacterial conjugation. Usually, the frequency of Tn1 transposition from plasmid pSA2001, a derivative of RP4, into the chromosome never exceeded 0.1% per cell. Percentage of His+ transconjugants, marked by transposon Tn1 during conjugation between Hfr donor, carrying plasmid pSA2001, and auxotrophic recipient, was about 30%. Transposon Tn1 transfer into the recipient cells does not depend on the recA+ gene function in donor cells or on conjugative transfer of plasmid pSA2001. The transfer requires the recA+ gene function in recipients as well as the Hfr function in donor cells. Southern's blot-hybridization revealed the insertion of transposon Tn1 into the different sites of the chromosome of His+ transconjugants. The transposon inserted during conjugation retains the ability to potential further translocation into new sites on the chromosomal DNA.     

Effects of moenomycin on Escherichia coli

The antibiotic moenomycin is a valuable biochemical tool for studying the metabolism of peptidoglycan and the autolytic system in Escherichia coli, since as a specific inhibitor of peptidoglycan polymerases it can efficiently promote cell lysis. In liquid media the bacteriolytic effect on E. coli K12 was dependent on the concentration of moenomycin, on growth phase and on growth rate. Before lysis cells underwent major morphological alterations. In sucrose-containing medium complete transformation to osmotically sensitive spheroplasts was easily achieved by addition of moenomycin. The minimum inhibitory concentration of the antibiotic varied with the strain of E. coli and was highly dependent on the growth medium. A tritiated derivative of moenomycin, [3H]decahydromoenomycin A, was prepared and found to have the same inhibiting efficiency. Its binding to E. coli membranes and membrane proteins was investigated. The absence of irreversible binding suggested that moenomycin might be a competitive inhibitor of the peptidoglycan polymerases. Spontaneous moenomycin resistant variants were isolated at a frequency of about 10(-9).     

Effects of sub-minimal inhibitory concentrations of EDTA on growth of Escherichia coli and the release of lipopolysaccharide

Abstract Release of lipopolysaccharide from E. coli was studied in the presence of sub-minimal inhibitory concentrations of ethylenediaminetetraacetic acid (EDTA). In untreated cells no release was detected with 50 mM Mg²⁺ in the medium, but a steady release of over 50% of the synthesized lipopolysaccharide was observed with 0.1 mM Mg²⁺. EDTA at MIC/8 led to a 2- to 3-fold higher release, presumably by an adjustment of the concentration of unchelated Mg²⁺ to a value still sustaining normal growth but giving rise to a highly unstable outer membrane. No structural difference was observed between cell-bound and released lipopolysaccharide.     

Cysteine, even in low concentrations, induces transient amino acid starvation in Escherichia coli.

Cysteine, in concentrations down to 0.04 micrograms/ml, induces transient amino acid starvation in Escherichia coli growing in minimal medium. The duration depends on the concentration and is 5 min at 2 micrograms of cysteine per ml. At low cysteine concentrations, threonine and isoleucine almost completely abolish the starvation.