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The antimicrobial activity of the peptide enantiomers cyclo[D-Tle-D-Lys-D-Tle-L-Ala-D-Tle-L-Ala-D-Tle-L-Ala] and cyclo[L-Tle-L-Lys-L-Tle-D-Ala-L-Tle-D-Ala-L-Tle-D-Ala] against Bacillus megaterium was investigated. Both these peptides showed very low activity in both an agar diffusion assay and a broth microdilution assay. However, when both peptides were present during the experiments a potent inhibition with an IC(50) value of 2 μM was observed. Furthermore, the peptides also showed low hemolytic activity. Neither peptide had any hemolytic activity in concentrations up to 1mM but when erythrocytes were exposed to both peptides a weak hemolytic activity could be observed with a HC(50) value of 316 μM., (Copyright © 2011. Published by Elsevier Ltd.)

The inactive components of the nicotinamide adenine dinucleotide (reduced form) (NADH) oxidase present in the 0.4% deoxycholate-soluble fraction obtained from Bacillus megaterium KM membranes were reaggregated into active NADH oxidase by dilution in the presence of Mg(2+). The reaggregated oxidase was different from the original membrane with respect to sedimentation behavior in a sucrose gradient and morphological appearance. The deoxycholate-insoluble portion of the membrane had membrane-like structure whereas the reaggregated oxidase appeared to be a filamentous aggregate of small particles. The reaggregated oxidase and the deoxycholate-insoluble membrane residue were similar to the original membrane with respect to total protein and total lipid content. The inactive components of the NADH oxidase system exist in deoxycholate as two molecular species which were separable by sucrose density gradient centrifugation or gel filtration in deoxycholate-containing solutions. Both components and dilution in the presence of Mg(2+) were necessary for restoration of oxidase activity. The smaller-molecular-weight component contained all of the NADH-2,6-dichlorophenolindophenol oxidoreductase activity of the original membrane.

Hexachlorophene is a soap-compatible bisphenol that has been widely used as an antiseptic, yet its mechanism of action is undefined. The relative threshold concentration for bactericidal effect on a susceptible test organism, Bacillus megaterium, was established to be about 10 mug/mg of cell dry weight. At this or at high (>/=100 mug/mg) concentration, adsorptive uptake by cells displayed saturation kinetics. At about 30 mug/mg, the time course of adsorption occurred in three distinct stages. The triphasic pattern was interpreted to represent successive penetration of and adsorption by the cell wall, the protoplast membrane, and the cytoplasm. This interpretation was substantiated by determinations of hexachlorophene adsorption by isolated cell components. Electron microscopy disclosed cytopathology, evidenced as gaps or discontinuities, in the protoplast membrane (but not in the cell wall or cytoplasm) at > 30 mug of hexachlorophene per mg of cell dry weight. Similarly, treatment with > 30 mug/mg allowed a fluorescigenic dye (tolyl-peri acid) to penetrate into the protoplast. However, no detectable cytological manifestations were discerned at the minimum lethal concentration of 10 mug/mg. Apparently, hexachlorophene is physically disruptive at intermediate or high relative concentrations but acts in a more subtle fashion at the minimal lethal concentration.

A method of fractionation of "ghosts" was devised to identify the chemical components of the cytoplasmic membrane. The method consists of dialyzing the "ghosts" against distilled water, and then dissolving the ghosts in dilute alkali. The ghosts were fractionated into four fractions by use of differential centrifugation. The components of each fraction were analyzed in detail. The ratio of lipid to protein and content of carbohydrate were found to be different for the four fractions. The main two fractions (fractions 2 and 3) contained several types of materials. Fraction 2, which is soluble in alkali and sedimentable at 105,000 x g, contained protein and lipid in the ratio of 2:1; ribonucleic acid was not detectable. Under the electron microscope, the ghosts appeared to have released the cell's cytoplasmic contents, but many small dense particles (about 100 A in diameter) remained adherent to the membrane surface. On the other hand, fraction 2 appeared to be made up only of a membrane structure. No 100 A particles were visible in this fraction. From these results, fraction 2 seemed to be pure membrane material.

A method is described for the detection of cholesterol in membranes from erythrocytes, mycoplasmas, and bacterial cells by a ferritin-labeling technique. Membranes treated with cereolysin, a bacterial hemolysin which specifically binds to cholesterol, and then treated with ferritin-antitetanolysin, were specifically ferritin-labeled for cholesterol. A similar antigen-antibody system, streptolysin O-ferritin-antistreptolysin, was also used successfully with erythrocyte membranes. There was an uneven distribution of ferritin in erythrocyte membranes suggesting that the distribution of cholesterol may not be entirely random. Mycoplasma gallisepticum was intensely labeled, but Acholeplasma laidlawii with or without cholesterol in the membranes was not labeled, suggesting an unusual location for cholesterol in A. laidlawii membranes. As controls, two of three species of bacterial membranes lacking cholesterol were not ferritin-labeled.