Pharmacodynamic parameters and hydrophobicity changes induced by meropenem in Acinetobacter baumannii.

The suppression of bacterial growth of four Acinetobacter baumannii strains after 60 min exposure to meropenem at supra-inhibitory concentrations (postantibiotic effect; PAE) or at supra-subinhibitory concentrations (postantibiotic-sub-MIC effect; PA SME) was studied. The duration of the PAE was dependent on antibiotic concentration and on the strain. Meropenem at 2x or 4x the minimum inhibitory concentration (MIC), with the exception of one strain treated with 4x MIC, did not provoke suppression of bacterial growth compared with untreated controls. The highest concentration of meropenem (8x MIC) induced PAE for the strains tested in the range of 0.6-6.9 h. The effect of supra-subinhibitory concentrations of meropenem (2x, 4x or 8x MIC + 0.2x MIC) on bacterial growth was more efficient compared with supra-inhibitory concentrations alone. Two out of the four strains treated did not renew their growth. Bacterial suspensions exposed to meropenem showed reduced surface hydrophobicity. Decreases in hydrophobicity were associated with longer PAE and PA SME depending on the strain.     

Effect of aminoglycosides on surface hydrophobicity of Acinetobacter baumannii

Effects of amikacin, gentamicin, netilmicin and tobramycin at subinhibitory concentrations (sub-MICs) (11/4, 1/8, 1/16 or 1/32 of their MICs) on the cell surface hydrophobicity of two Acinetobacter baumannii strains (7194 and 16265) were evaluated. Hydrophobicity was determined by two different methods - by adherence of bacteria to hydrocarbon (xylene) and by aggregation of bacteria in ammonium sulphate solutions at various concentrations. The adherence of A. baumannii strains to xylene decreased, mainly, after treatment with netilmicin at 1/4, 1/8 or 1/16 of the MIC (to 6.4%, 17.0% or 24.5% of the control value) (strain 7194) and after treatment with amikacin and gentamicin at 1/4 of their MICs (to 58.4% or 54.4%) (strain 16265). A decrease in surface hydrophobicity of exposed strains under these conditions was shown in salting-out test, too. Tobramycin reduced hydrophobic properties of A. baumannii strains at all tested sub-MICs to only a small extent.     

Cell surface hydrophobicity of colistin-susceptible vs resistant Acinetobacter baumannii determined by contact angles: methodological considerations and implications

Contact angle analysis of cell surface hydrophobicity (CSH) describes the tendency of a water droplet to spread across a lawn of filtered bacterial cells. Colistin‐induced disruption of the Gram‐negative outer membrane necessitates hydrophobic contacts with lipopolysaccharide (LPS). We aimed to characterize the CSH of Acinetobacter baumannii using contact angles, to provide insight into the mechanism of colistin resistance. Contact angles were analysed for five paired colistin‐susceptible and resistant Ac. baumannii strains. Drainage of the water droplet through bacterial layers was demonstrated to influence results. Consequently, measurements were performed 0·66 s after droplet deposition. Colistin‐resistant cells exhibited lower contact angles (38·8±2·8–46·8±1·3°) compared with their paired colistin‐susceptible strains (40·7±3·0–48·0±1·4°; anova ; P < 0·05). Contact angles increased at stationary phase (50·3±2·9–61·5±2·5° and 47·4±2·0–50·8±3·2°, susceptible and resistant, respectively, anova ; P < 0·05) and in response to colistin 32 mg l^?1 exposure (44·5±1·5–50·6±2·8° and 43·5±2·2–48·0±2·2°, susceptible and resistant, respectively; anova ; P < 0·05). Analysis of complemented strains constructed with an intact lpxA gene, or empty vector, highlighted the contribution of LPS to CSH. Compositional outer‐membrane variations likely account for CSH differences between Ac. baumannii phenotypes, which influence the hydrophobic colistin–bacterium interaction. Important insight into the mechanism of colistin resistance has been provided. Greater consideration of contact angle methodology is necessary to ensure accurate analyses are performed.     

Molecular orientation of tropoelastin is determined by surface hydrophobicity

Tropoelastin is the precursor of the extracellular protein elastin and is utilized in tissue engineering and implant technology by adapting the interface presented by surface-bound tropoelastin. The preferred orientation of the surface bound protein is relevant to biointerface interactions, as the C-terminus of tropoelastin is known to be a binding target for cells. Using recombinant human tropoelastin we monitored the binding of tropoelastin on hydrophilic silica and on silica made hydrophobic by depositing a self-assembled monolayer of octadecyl trichlorosilane. The layered organization of deposited tropoelastin was probed using neutron and X-ray reflectometry under aqueous and dried conditions. In a wet environment, tropoelastin retained a solution-like structure when adsorbed on silica but adopted a brush-like structure when on hydrophobized silica. The orientation of the surface-bound tropoelastin was investigated using cell binding assays and it was found that the C-terminus of tropoelastin faced the bulk solvent when bound to the hydrophobic surface, but a mixture of orientations was adopted when tropoelastin was bound to the hydrophilic surface. Drying the tropoelastin-coated surfaces irreversibly altered these protein structures for both hydrophilic and hydrophobic surfaces.     

Alterations induced in mouse chromosomes by restriction endonucleases

Fixed chromosomes of mouse have been treated with Alu I, Eco RII, Hind III or Bam HI restriction endonucleases and subsequently stained with either Giemsa, Ethidium Bromide or Acridine Orange. The results obtained have been discussed in the light of preferential or non-preferential extraction of DNA from specific chromosome areas following enzyme digestion. The possible involvement of a particular structural organization of some classes of heterochromatin has been hypothesized to account for the findings after Alu I or Eco RII treatment. The meaning of the Giemsa banding observed after Hind III or Bam HI digestion has also been considered, in comparison to the different stain responses obtained by using a DNA-specific dye such as Ethidium Bromide.     

Alterations in membrane surfaces induced by attachment of carbohydrates

We have examined the behavior of the dry phospholipid dipalmitoylphosphatidylcholine (DPPC) in the presence of several carbohydrate derivatives. These carbohydrate derivatives possess a hydrophobic portion which is incorporated directly into the DPPC membrane and a hydrophilic portion which places the carbohydrate structure at the membrane interface with the surrounding matrix. In the presence of these derivatives, the physical properties of the membrane are altered. These alterations are evident in changes observed in the phosphate and carbonyl vibrational modes of the phospholipid portion of the membrane. In addition, the phase transition behavior of the lipid is significantly altered as evidenced by a reduction in the gel to liquid-crystalline phase transition temperature. These results are consistent with those previously reported for free carbohydrates interacting with membranes in which a water replacement hypothesis has been used to explain the behavior. The attachment of carbohydrates to the membrane enhances these effects by localizing the agent responsible for these alterations at the membrane interface.     

Autoaggregation and surface hydrophobicity of bifidobacteria

Thirteen strains of four different Bifidobacterium spp. were observed for their autoaggregation ability and surface hydrophobicity, and correlation between these two traits was determined. Bifidobacteria were classified into high, medium and low autoaggregation strains according to autoaggregation ratio measured from changes in absorbance of media. High autoaggregation strains showed microscopic clustering of cells, whereas low and medium autoaggregation strains showed no such clustering. Autoaggregation ability decreased in high autoaggregation strains but increased in medium and low autoaggregation strains when the assay was performed at higher temperature (37°C compared with 25 and 10°C). Bacterial strains belonging to the high, medium or low autoaggregation group were correlated in terms of their surface hydrophobicity and evaluated based on changes in absorbance of the bacterial suspension before and after extraction with xylene. These results indicate that autoaggregation ability, together with surface hydrophobicity and microscopic image could be used for evaluating the adhesion ability of potential probiotic bifidobacterial strains. Moreover, a synergistic effect of pH and media may be involved in autoaggregation.     

Alterations of energy metabolism induced by hexadecane in mice

Two groups of young male OF-1 mice were fed for 60 days with cafeteria or, as controls, with standard pellet diet respectively. At that time, both groups were daily treated with hexadecane (HDK) on the skin. HDK induced a drastic body weight loss much higher in cafeteria than control mice. White adipose tissue were exhausted after 4 days of treatment in controls but not after 10 days in cafeteria ones. HDK resulted in mobilization of liver glycogen in both groups while muscle glycogen decreased slightly in the end. Hexadecane treatment did not result in massively enhanced nitrogen metabolism, as the actual oxidation of amino acids decreased considerably as indicated by the low levels of plasma urea. The results could be explained by powerful and lasting effects of hexadecane on thermogenesis and metabolic reserve balance. The use of this material for pharmacological manipulation of body weight appeared difficult.     

Expression of surface hydrophobicity encoded by R-plasmids in Escherichia coli laboratory strains

The inclusion of drug-resistance plasmids (R-plasmids) in Escherichia coli strains has been shown to determine the formation of specific surface structures which could modify bacterial surface characteristics relevant for pathogenic processes.Thirtyone R-plasmids (from different incompatibility groups) have been transferred to three E. coli laboratory strains, and surface hydrophobicity modifications have been measured by three methods: salting-out, adsorption to hexadecane and adsorption to xylene.The results obtained show that the presence of R-plasmids produced variations which are dependent on the receptor strains and measuring method employed. Also, it has been found that the plasmids behave differently depending on the strain in which they are included.The results obtained by the salting-out method are not correlative with those obtained by adsorption to hydrocarbons, probably due to the implication of different hydrophobic molecules in the interaction with salt or hydrocarbons.Concluding, the choice of receptor strain and measuring method are of great importance for the investigation of surface hydrophobicity (and probably other characteristics) encoded by R-plasmids.Abbreviations TSB Trypticase soya broth - TSA trypticase soya agar     

High surface hydrophobicity ofStaphylococcus aureus as revealed by hydrophobic interaction chromatography

Hydrophobic interaction chromatography (HIC) on Octyl Sepharose^R in a column procedure was used to compare the relative surface hydrophobicity ofStaphylococcus aureus reference strains, protein A-negative mutants, and strains isolated from bovine mastitis. High protein A-producing strains (Cowan 1 and clinical isolate SA 17970) showed a higher relative surface hydrophobicity than did strains producing a low amount of protein A. One encapsulatedS. aureus strain (Smith diffuse) did not bind to the gel, while an unencapsulated variant showed binding properties similar to weak protein A-producing strains. Studies onS. aureus strains isolated from bovine mastitis revealed a good correlation between adsorption to Octyl Sepharose and the production of protein A. Results indicate that protein A and probably other surface proteins such as fibronectin-binding protein contribute to the high relative surface hydrophobicity ofS. aureus.     

Flocculence of Saccharomyces cerevisiae cells is induced by nutrient limitation, with cell surface hydrophobicity as a major determinant.

Initiation of flocculation ability of Saccharomyces cerevisiae MPY1 cells was observed at the moment the cells stop dividing because of nitrogen limitation. A shift in concentration of the limiting nutrient resulted in a corresponding shift in cell division and initiation of flocculence. Other limitations also led to initiation of flocculence, with magnesium limitation as the exception. Magnesium-limited S. cerevisiae cells did not flocculate at any stage of growth. Cell surface hydrophobicity was found to be strongly correlated with the ability of the yeast cells to flocculate. Hydrophobicity sharply increased at the end of the logarithmic growth phase, shortly before initiation of flocculation ability. Treatments of cells which resulted in a decrease in hydrophobicity also yielded a decrease in flocculation ability. Similarly, the presence of polycations increased both hydrophobicity and the ability to flocculate. Magnesium-limited cells were found to be strongly affected in cell surface hydrophobicity. A proteinaceous cell surface factor(s) was identified as a flocculin. This heat-stable component had a strong emulsifying activity, and appears to be involved in both cell surface hydrophobicity and in flocculation ability of the yeast cells.     

Flocculence of Saccharomyces cerevisiae cells is induced by nutrient limitation, with cell surface hydrophobicity as a major determinant.

Initiation of flocculation ability of Saccharomyces cerevisiae MPY1 cells was observed at the moment the cells stop dividing because of nitrogen limitation. A shift in concentration of the limiting nutrient resulted in a corresponding shift in cell division and initiation of flocculence. Other limitations also led to initiation of flocculence, with magnesium limitation as the exception. Magnesium-limited S. cerevisiae cells did not flocculate at any stage of growth. Cell surface hydrophobicity was found to be strongly correlated with the ability of the yeast cells to flocculate. Hydrophobicity sharply increased at the end of the logarithmic growth phase, shortly before initiation of flocculation ability. Treatments of cells which resulted in a decrease in hydrophobicity also yielded a decrease in flocculation ability. Similarly, the presence of polycations increased both hydrophobicity and the ability to flocculate. Magnesium-limited cells were found to be strongly affected in cell surface hydrophobicity. A proteinaceous cell surface factor(s) was identified as a flocculin. This heat-stable component had a strong emulsifying activity, and appears to be involved in both cell surface hydrophobicity and in flocculation ability of the yeast cells.     

Autoaggregating Yersinia enterocolitica express surface fimbriae with high surface hydrophobicity

For 13 strains of Yersinia enterocolitica , there was a good correlation between the production of the broad-spectrum, mannose-resistant Yersinia haemagglutinin (MR/Y HA), the presence of fimbriae and high surface hydrophobicity. Each of these characters was expressed in cultures grown at low (< 32°C) but not at high (> 35°C) temperatures.     

Alterations in the rat electrocardiogram induced by stationary magnetic fields

A field strength dependent increase in the amplitude of the T-wave signal in the rat electrocardiogram (ECG) was observed during exposure to homogeneous, stationary magnetic fields. For 24 adult Sprague-Dawley and Buffalo rats of both sexes, the T-wave amplitude was found to increase by an average of 408% in a 2.0 Tesla (1 Tesla = 10⁴ Gauss) field. No significant magnetically induced changes were observed in other components of the ECG record, including the P wave and the QRS complex. The minimum field level at which augmentation of the T wave could be detected was 0.3 Tesla. The magnetically induced increase in T-wave amplitude occurred instantaneously, and was immediately reversible after exposure to fields as high as 2.0 Tesla. No abnormalities in any component of the ECG record, including the T wave, were noted during a period of 3 weeks following cessation of a continuous 5-h exposure of rats to a 1.5-Tesla field. The heart rate and breathing rate of adult rats were not altered during, or subsequent to, application of fields up to 2.0 Tesla. The effect of animal orientation within the field was tested using juvenile rats 3–14 days old. The maximum increase in T-wave amplitude was observed when subjects were placed with the long axis of the body perpendicular to the lines of magnetic induction. These experimental observations, as well as theoretical considerations, suggest that augmentation of the signal amplitude in the T-wave segment of the ECG may result from a superimposed electrical potential generated by aortic blood flow in the presence of a stationary magnetic field.     

Increased cell surface hydrophobicity associated with possession of an additional surface protein by Aeromonas salmonicida

Abstract The cell surface of strains of Aeromonas salmonicida possessing an additional surface protein (A-protein) was shown to be more hydrophobic than strains devoid of this protein, using the techniques of phase partitioning, agglutination in the presence of ammonium sulphate and hydrophobic interaction chromatography.     

Autoaggregating Yersinia enterocolitica express surface fimbriae with high surface hydrophobicity

For 13 strains of Yersinia enterocolitica, there was a good correlation between the production of the broad-spectrum, mannose-resistant Yersinia haemagglutinin (MR/Y HA), the presence of fimbriae and high surface hydrophobicity. Each of these characters was expressed in cultures grown at low (less than 32 degrees C) but not at high (Greater than 35 degrees C) temperatures.