Action of steroidal diamines on active transport and permeability properties of Escherichia coli

Microbial toxicity of ethanolamines--multiwalled carbon nanotubes

In the present study, antimicrobial activities of multiwalled carbon nanotubes (MWCNTs) functionalized with ethanolamine (EA) groups were investigated. Therefore, MWCNT were first functionalized with mono-, di-, and triethanolamine (MEA, DEA, and TEA) under microwave technique. Development of functional groups on the MWCNT surface was confirmed by Fourier transform infrared and thermogravimetric analysis. Morphological variation was investigated by transmission electron microscopy. Then, antimicrobial activities of pristine and functionalized MWCNT (MWCNT-MEA, -DEA, and -TEA) were tested against different bacteria species. The studies have been done on four Gram-negative bacteria (Escherichia coli, Klebsiella pneumonia, Pseudomonas aeroginosa, and Salmonella typhimurium) as well as four Gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus, Bacillus cereus, and Streptococcus pneumonia). The results based on minimal inhibitory concentration and radial diffusion assay were shown that the antimicrobial activity of MWCNT-TEA > MWCNT-DEA > MWCNT-MEA > pristine MWCNT. Based on the results, it seems that EA groups could play an important role in antimicrobial activity of MWCNT.

Mechanism of colicin action: early events

The kinetics and the temperature dependence of potassium loss from Escherichia coli cells treated with colicin K have been examined. At 37 C, after a single lethal hit, essentially all of the intracellular potassium is lost within the first few minutes of treatment. The initial rate of loss is linearly related to colicin concentration up to a multiplicity of 30. As the temperature is decreased over the range from 37 to 1 C, an increasing delay is seen in the initiation of potassium loss after colicin adsorption. This delay can be overcome by increasing colicin multiplicity and probably reflects an alteration of the cell membrane at these temperatures. A comparison of this effect with an apparently related effect of temperature on the action of irehdiamine A indicates that the delay may represent the inhibition of a transmission process occurring in the membrane.

Mammalian steroid hormones are substrates for the major RND- and MFS-type tripartite multidrug efflux pumps of Escherichia coli

A steroid-hormone-dependent growth suppression was observed in Escherichia coli efflux-deficient backgrounds containing mutations in the major RND- and MFS-type tripartite multidrug efflux systems, AcrAB-TolC and EmrAB-TolC, respectively. In addition to their previously known natural steroid spectrum, which includes bile acids, both systems were shown to transport the hormones estradiol and progesterone, whereas hydrocortisone served as a substrate of only AcrAB-TolC. Furthermore, at least two other RND-type pumps, YhiV and AcrD, were capable of transporting such hormones when overexpressed on plasmid vectors (with some demonstrable specificity observed with AcrD). When this activity was examined in a wild-type background, cell-associated estradiol levels remained largely unaffected by competition with exogenous bile acids and hydrocortisone, in contrast to progesterone, which produced a significant modulation in estradiol uptake.

Antibacterial activity of 15-azasteroids alone and in combination with antibiotics

A new class of 15-azasteroid analogues has been synthesized and tested for antimicrobial activity. The compounds 1, 10, 11, 11a-tetrahydro-7-methoxy-11a-methyl-2H-naphth (1,2-g) indol (methoxyimine) and 1,10,11,11a-tetrahydro-11a-methyl-2H-naphth (1,2-g) indol-7-ol (hydroxyimine) inhibit the growth of Bacillus subtillis and Escherichia coli at concentrations as low as 10-5 M. Addition of either compound to the growth medium casued a rapid inhibition in the transport of radioactive glucose, uracil and several amino acids. The inhibition of growth and substrate transport was reversed following removl of the steroid from the medium. The evidence is consistent with a site of steroid action at the cell periphery. Combining the methoxyimine with polyor circulin at subinhibitory concentrations produced greatly enhanced antimicrobial activity against Pseudomonas fluorescens. Similar action was observed against B. subtilis when the azasteroid was combined with vancomycin or chloramphenicol. The inhibitory action of other antibiotics such as penicillin or erythromycin was not affected by addition of the test compound. The results suggest formation of a molecular complex between the azasteroid and antibiotic which is responsible for the enhanced biological activity.

Relationship of chemical structure and antimicrobial activity of alkyl amides and amines

Contrary to the limited effects of alkyl amides and their corresponding N-derivatives, alkyl amines affected both gram-positive and gram-negative organisms. As with other alkyl derivatives the most sensitive gram-negative bacteria were usually more resistant than the most resistant gram-positive bacteria. Compounds with a chain-length of 11 to 15 are most active. Although some of the general properties relating the activity of fatty acids to their antimicrobial action are similar to those of amine compounds, the amines are unique in that monounsaturation does not increase compound activity. The possible modes of action of these compounds are discussed.

Active transport of magnesium in escherichia coli

Magnesium-28 is accumulated by cells of Escherichia coli by a process that is temperature-dependent and inhibited by dinitrophenol and cyanide. The rate of uptake of magnesium is concentration-dependent, with a "K(m)" of about 5 x 10(-4)M in tryptone broth. There is evidence for cellular control over this rate. The magnesium accumulation system is specific, since neither potassium nor calcium (nor apparently manganese) competes with magnesium for cellular uptake. The magnesium that is accumulated by the cells can be released by treatment with toluene and partially exchanges with excess exogenous magnesium.