Hydrophobic properties of gram-negative rods colonizing upper respiratory tract of healthy people

The cell surface hydrophobicity is one of the non specific factors of adhesion influencing the ability of microorganisms to colonize nasopharynx. The aim of this paper was to evaluate via salt aggregation test (SAT) the cell surface hydrophobicity of 150 strains of gram-negative rods isolated from the throat or/and nasal specimens of healthy people. It has been found that among the nonfermenting rods hydrophobic strains were predominant. In contrast, the isolates of Enterobacteriaceae family were characterized by the distinctive features of the cell surface within particular genera or even species. The obtained results show that, despite differences in cell surface hydrophobicity, numerous species of gram-negative rods have the ability to colonize the mucous membrane of upper respiratory tract. This suggests that the cell surface hydrophobicity is rather a feature of species or genus, but it is not related to the ecological niche of microorganisms in human body.     

Comparative studies on surface hydrophobicity of streptococcal strains of groups A, B, C, D and G

Cell surface hydrophobicity of group A, B, C, D and G streptococcal strains has been studied and compared in a new test based on the fact that the degree of bacterial aggregation in ammonium sulphate depends on amphiphilic surface antigens. M-positive group A strains showing good growth in normal human blood aggregated in the standard salt aggregation test at very low concentrations of ammonium sulphate, while M-negative strains, which were killed in normal human blood, usually aggregated at high salt concentrations. Agents such as 2 M-KSCN, 2 M-guanidine. HC1 or 2 M-urea decreased the aggregation of the M-positive strains in the salt aggregation test while non ionic detergents such as Tween 20 (1%, w/v) and ethylene glycol (2 M) did not affect cell aggregation. Binding of fibrinogen and albumin resulted in a decrease of surface hydrophobicity of the group A M-positive strains. Group B strains possess a hydrophilic surface character and did not aggregate, while group C and G strains behaved in the salt aggregation test like M-negative strains of group A streptococci. Group D strains did not aggregate even at high ammonium salt concentrations. The results are discussed in relation to the influence of lipoteichoic acid and other surface antigens on strains of the various groups, and it is suggested that M protein and possibly also other surface proteins contribute to the high surface hydrophobicity of group A strains.     

Effect on cell surface hydrophobicity and susceptibility of Helicobacter pylori to medicinal plant extracts

Effects on aqueous extracts of medicinal plants on ten Helicobacter pylori strains were studied by the salt aggregation test to determine the possibility to modulate their cell surface hydrophobicity and by an agar diffusion assay for detection of antimicrobial activity. It was established that aqueous extracts of bearberry and cowberry leaves enhance cell aggregation of all H. pylori strains tested by the salt aggregation test, and the extract of bearberry possessed a remarkable bacteriostatic activity. Pure tannic acid showed a result similar to that of bearberry and cowberry extracts which contained a large amount of tannins. In contrast, extracts of wild camomile and pineapple-weed, which blocked aggregation of H. pylori, contained small amounts of tannins and did not reveal any antimicrobial activity. Tannic acid seems to be the component of bearberry and cowberry aqueous extracts with the highest activity to decrease cell surface hydrophobicity as well as in antibacterial activity against H. pylori.     

Cell surface hydrophobicity ofStaphylococcus aureus measured by the salt aggregation test (SAT)

Well-defined laboratory strains as well as 72 clinical strains ofStaphylococcus aureus isolated from bovine mastitis were investigated for surface hydrophobicity by the salt aggregation test (SAT).Staphylococcus aureus strain Cowan 1, rich in protein A and fibronectin-binding surface proteins, was found to show high surface hydrophobicity, whereas strain Wood 46, deficient in these surface proteins, showed low surface hydrophobicity. SAT showed a significant difference in surface hydrophobicity (P<0.001) between protein A-positive and A-negative strains measured by ²-test analysis. Comparison of SAT values with results obtained from hydrophobic interaction chromatography (HIC) showed a good correlation (P<0.025). A high-level protein-A-producing mutant (SA 113prA-3) showed increased surface hydrophobicity as compared with the parent strain (SA 113), whereas ten protein-A-negative mutants showed low surface hydrophobicity in SAT. Of the 72 clinical isolates tested by SAT, 47 (65%) showed autoaggregating properties, i.e., the strains aggregated even in isotonic buffers. Tween 80 (1% vol/vol) and ethylene glycol (50% vol/vol) prevented autoaggregation of some hydrophobic strains aggregating in phosphate-buffered saline. However, 2M of a chaotropic agent (NaSCN) was more efficient in preventing autoaggregation of the strains tested. Heating of cell suspensions to 80°C or 100°C as well as trypsin andStreptomyces griseus protease treatment generally caused a decrease in the cell surface hydrophobicity. This indicates that protein A, fibronectin-binding proteins, and probably other as yet unidentified proteins contribute to the high surface hydrophobicity of most strains isolated from bovine mastitis.     

Effect of milk on surface properties of Staphylococcus aureus from bovine mastitis

Abstract The surface hydrophobicity of cells of Staphylococcus aureus strains isolated from bovine mastitis grown on conventional agar and broth media was drastically reduced after incubation with bovine milk. Strains grown in high carbohydrate-high salt media yielded cells with reduced surface hydrophobicity compared to cells grown in conventional media, and adding bovine milk to minimal medium also yielded cells with reduced surface hydrophobicity, as determined by hydrophobic interaction chromatography and the salt aggregation test. Incubation of strains in milk and growth in a medium supplemented with bovine milk also significantly changed bacterial surface charge as determined by free-zone electrophoresis. Strains with high or with decreased adsorptive and aggregating properties did not produce surface capsule or slime. Heat treatment (60° C or 80° C) of the bacterial suspensions did not significantly change their adsorptive and aggregating properties.     

Low cell surface hydrophobicity is one of the key factors for high butanol tolerance of Lactic acid bacteria

Highly butanol‐tolerant strains have always been attractive because of their potential as microbial hosts for butanol production. However, due to the amphiphilic nature of 1‐butanol as a solvent, the relationship between the cell surface hydrophobicity and butanol resistance remained ambiguous to date. In this work, the quantitatively estimated cell surface hydrophobicity of 74 Lactic acid bacteria strains were juxtaposed to their tolerance to various butanol concentrations. The obtained results revealed that the strains’ hydrophobicity was inversely proportional to their butanol tolerance. All highly butanol‐resistant strains were hydrophilic (cell surface hydrophobicity<1%), whereas the more hydrophobic the strains were, the more sensitive to butanol they were. Furthermore, cultivation at increasing butanol concentrations showed a clear tendency to decrease the level of hydrophobicity in all tested organisms, thus suggesting possible adaptation mechanisms. Purposeful reduction of cell surface hydrophobicity (by removal of S‐layer proteins from the cell envelope) also led to an increase of butanol resistance. Since the results covered 23 different Lactic acid bacteria species of seven genera, it could be concluded that regardless of the species, the lower degree of cells’ hydrophobicity clearly correlates with the higher level of butanol tolerance.     

Cell surface hydrophobicity and charge of Staphylococcus aureus and coagulase-negative staphylococci from bovine mastitis

The effects of seven growth media on cell surface hydrophobicity of a collection of Staphylococcus aureus and coagulase-negative staphylococci isolated from bovine mastitis were compared in the salt-aggregation test. Thirty-three per cent of Staph. aureus strains showed extremely high cell surface hydrophobicity (auto-aggregated) and 28% were moderately hydrophobic while 26% were hydrophilic after growth on horse blood agar at 37 degrees C for 18 h. There were great variations in the proportion and degree of the hydrophobicity depending on the medium used. Cultivations on/in capsule-inducing media caused a shift from a high to a low degree of hydrophobicity, although a microscopically detectable capsule or slime layer was seen in only one strain. This strain and encapsulated reference strains had a hydrophilic cell surface and migrated faster in free zone electrophoresis than cells of unencapsulated strains. Cells of strains grown on staphylococcus medium 110 agar migrated faster than those grown on horse blood agar regardless of their capsule production. Coagulase-negative staphylococci showed uniformly hydrophilic cell surface after cultivation on horse blood agar, but not when grown in tryptic soy broth or proteose peptone broth. It was concluded that most of the Staph. aureus strains from bovine mastitis under a variety of growth conditions in stationary phase culture constantly expressed hydrophobic cell surface.     

Effects of Bacillus anthracis hydrophobicity and induction of host cell death on sample collection from environmental surfaces

The objective of this study is to determine whether DNA signature recovery of Bacillus anthracis strains from different environmental substrates correlates with pathogen cell surface hydrophobicity and induction of host cell death. We compared recovery of DNA signatures from a panel of B. anthracis strains collected from two environmental substrates, non-porous surfaces and soil, using real-time qPCR. We further assessed both cell surface hydrophobicity of the B. anthracis strains by contact angle measurements and host cell viability in response to B. anthracis infection in a mouse macrophage cell model system. Our studies demonstrated correlation between reduced B. anthracis sample recovery from environmental substrates and increased cell surface hydrophobicity. Surprisingly, the most hydrophilic strain, K4596, which exhibited the highest level of recovery from the environmental surfaces, induced the highest level of host cell cytotoxicity compared to more hydrophobic B. anthracis strains in the panel. Our results suggest that cell surface hydrophobicity may play a leading role in mediating pathogen adherence to environmental surfaces. These findings can contribute to the optimization of pathogen detection efforts by understanding how bacterial parameters such as hydrophobicity and induction of host cell death affect bacterial adherence to environmental surfaces.     

Cell surface hydrophobicity and charge of Staphylococcus aureus and coagulase-negative staphylococci from bovine mastitis

The effects of seven growth media on cell surface hydrophobicity of a collection of Staphylococcus aureus and coagulase-negative staphylococci isolated from bovine mastitis were compared in the salt-aggregation test. Thirty-three per cent of Staph. aureus strains showed extremely high cell surface hydrophobicity (auto-aggregated) and 28% were moderately hydrophobic while 26% were hydrophilic after growth on horse blood agar at 37°C for 18 h. There were great variations in the proportion and degree of the hydrophobicity depending on the medium used. Cultivations on/in capsule-inducing media caused a shift from a high to a low degree of hydrophobicity, although a microscopically detectable capsule or slime layer was seen in only one strain. This strain and encapsulated reference strains had a hydrophilic cell surface and migrated faster in free zone electrophoresis than cells of unencapsulated strains. Cells of strains grown on staphylococcus medium 110 agar migrated faster than those grown on horse blood agar regardless of their capsule production. Coagulase-negative staphylococci showed uniformly hydrophilic cell surface after cultivation on horse blood agar, but not when grown in tryptic soy broth or proteose peptone broth. It was concluded that most of the Staph. aureus strains from bovine mastitis under a variety of growth conditions in stationary phase culture constantly expressed hydrophobic cell surface.     

Cell surface hydrophobicity and macrophage association ofAeromonas salmonicida

Hydrophobic interaction chromatography and salt aggregation were used to compare the call surface hydrophobicity of strains of the fish pathogenAeromonas salmonicida which differed in their ability to produce the surface protein array known as A-layer. Presence of this superficial protein layer is crucial to the virulence of this organism and was found to coincide with a dramatic increase in cell surface hydrophobicity. Assays with in vitro cultured macrophages from either rainbow trout or mice revealed that this hydrophobic A-layer providedA. salmonicida cells with an enhanced ability to associate with phagocytic monocytes. This enhanced association was demonstrated in the absence of opsonizing antibody and may have important implications in the virulence ofA. salmonicida for fish.     

Yeast and bacteria cell hydrophobicity and hydrocarbon biodegradation in the presence of natural surfactants: rhamnolipides and saponins

This study concerns the relation between hydrocarbon biodegradation in the presence of natural surfactants and cell hydrophobicity resulting from the use of these surfactants. The relative capabilities of two bacterial strains (Pseudomonas aeruginosa and Bacillus subtilis) and two yeast strains (Candida maltosa, Yarrowia lipolytica) were investigated. The selected microorganisms were tested separately and in combination in order to achieve the optimal degrading performance. The surface cell hydrophobicity of microorganisms and the degree of hydrocarbon biodegradation were measured. The microbial adhesion to the hydrocarbon (MATH) test was used to denote the surface cell hydrophobicity of the microbial species. The results indicate the correlation between the modification of the surface cell and the degree of hydrocarbon biodegradation; however results for bacteria differ from that obtained for yeast strains. Saponins, as the surfactant, was more effective than rhamnolipides during hydrocarbon biodegradation, though the concentration of this surfactant has no significant influence on the surface cell hydrophobicity.     

A comparison of various methods to determine hydrophobic properties of streptococcal cell surfaces

In order to determine whether various methods which are commonly applied to determine the hydrophobicity of bacterial cell surfaces yield similar results, the hydrophobicity of a range of oral streptococcal isolates was measured using various methods including adsorption to hexadecane, hydrophobic interaction chromatography, salt-aggregation and contact angle measurements. In addition the zela potential and the adhesion to saliva-coated hydroxyapatite were determined. To compare the results of the different methods, linear and rank correlation coefficients were calculated. The resulting correlations were weak when applied to the whole range of strains even in those cases where the tests are expected to probe the same surface characteristics. However, generally good correlations were obtained when a set of strains was examined which were derived from a single parent strain and which only differed in defined surface structures. Accordingly it must be concluded from the methods applied here, that if is not possible to define the surface ‘hydrophobicity’ of a bacterium other than on a comparative level with closely related strains. No clear correlation was found between any hydrophobicity test and the adhesion to saliva-coated hydroxyapatite.     

Influence of the growth conditions on the hydrophobicity of Renibacterium salmoninarum evaluated by different methods

The influence of medium and salinity on the cell surface hydrophobicity of Renibacterium salmoninarum was investigated using three different methods: bacterial adherence to hydrocarbons (BATH), salt agglutination test (SAT), and binding to nitrocellulose filters (NCF). The possible relationship among hydrophobicity, haemagglutination and adherence to cell lines was also evaluated. R. salmoninarum showed to be highly hydrophobic regardless of the growth conditions or technique employed. Nevertheless, slight differences can be detected depending on the method used. In the SAT and NCF assays very uniform values were obtained within the strains. All the R. salmoninarum isolates agglutinated in (NH4)2SO4 in a range of 0.05-0.2 M and displayed a 77-100% of adherence to nitrocellulose filters. However, more variable results were observed in the BATH method depending on the hydrocarbon, buffer and strain employed. Although all of the isolates produced haemagglutinins for homeotherm erythrocytes, the majority of them failed to agglutinate poikilothermic red blood cells and were unable to adhere to fish cell lines. Therefore, a general correlation among hydrophobicity, agglutinating capacity for fish erythrocytes and adherence to fish cells can not be established for R. salmoninarum.     

Standardization of salt aggregation test for reproducible determination of cell-surface hydrophobicity with special reference to Staphylococcus species

The laboratory conditions for reproducible routine determination of staphylococcal cell-surface hydrophobicity by the salt aggregation test were standardized. Fresh bacterial suspensions standardized to 5 x 10(9) cfu/ml gave the most reproducible results with both Staphylococcus aureus and coagulase-negative staphylococci. For relatively hydrophobic strains a 5-min reading time was necessary to detect bacterial aggregation in ammonium sulphate solutions ranging from 0.1 M to 1.5 M, pH 6.8. A x 10 hand lens facilitated reading aggregations. Overnight storage of bacterial suspensions at 20 degrees C reduced cell-surface hydrophobicity of all species, while storage at 4 degrees C reduced the hydrophobic nature of Staph. aureus strains. The hydrophobicity of coagulase-negative staphylococci rarely changed at 4 degrees C. A 10-fold dilution of fresh, standardized bacterial suspensions made it impossible to detect bacterial aggregation in ammonium sulphate solutions even with a hand lens. Under standardized conditions three types of staphylococcal cell aggregations were observed. The first looked like the slide agglutination for O antigens of Enterobacteriaceae, the second resembled H-agglutination, while the third had a filamentous appearance. These patterns indicated that more than one component might contribute to cell-surface hydrophobicity of both Staph. aureus and coagulase-negative staphylococci, or the same component might have different position on the cell surface.     

Hydrophobic and adhesive capacity of Candida strains isolated from patients with fungal infection

The aim of this study was to evaluate hydrophobicity of fungal strains of Candida sp. isolated from clinical materials of patients with fungal infections. Two hundred and eighty one strains of C. albicans and 29 strains belonging to the other species of Candida were tested in salt aggregation test (SAT). Strong hydrophobicity (autoaggregation in the test) was found in 29.4% of tested strains. The majority of them was isolated from vagina. In 20 randomly selected strains hydrophobicity was measured not only by salt aggregation test but also by hydrophobic interaction chromatography (MIC). The ability to attach to buccal epithelial cells in vitro was compared between 50 strongly hydrophobic strains and 30 with low hydrophobicity. The former strains attached significantly stronger (p less than 0.001).     

Standardization of salt aggregation test for reproducible determination of cell-surface hydrophobicity with special reference to Staphylococcus species

The laboratory conditions for reproducible routine determination of staphylococcal cell-surface hydrophobicity by the salt aggregation test were standardized. Fresh bacterial suspensions standardized to 5 times 10⁹ cfu/ml gave the most reproducible results with both Staphylococcus aureus and coagulase-negative staphylococci. For relatively hydrophobic strains a 5-min reading time was necessary to detect bacterial aggregation in ammonium sulphate solutions ranging from 0.1 M to 1.5 M, pH 6.8. A × 10 hand lens facilitated reading aggregations. Overnight storage of bacterial suspensions at 20C reduced cell-surface hydrophobicity of all species, while storage at 4C reduced the hydrophobic nature of Staph. aureus strains. The hydrophobicity of coagulase-negative staphylococci rarely changed at 4C. A 10-fold dilution of fresh, standardized bacterial suspensions made it impossible to detect bacterial aggregation in ammonium sulphate solutions even with a hand lens. Under standardized conditions three types of staphylococcal cell aggregations were observed. The first looked like the slide agglutination for O antigens of Enterobacteriaceae, the second resembled H-agglutination, while the third had a filamentous appearance. These patterns indicated that more than one component might contribute to cell-surface hydrophobicity of both Staph. aureus and coagulase-negative staphylococci, or the same component might have different position on the cell surface.     

The correlation between surface hydrophobicity and adherence of Bifidobacterium strains from centenarians' faeces

To develop food-grade bifidobacteria micro-ecologics, screening for Bifidobacteria strains which can adhere to intestinal epithelial cells was finished. Twenty-three bifidobacterial strains tested were isolated from centenarians in Bama country, the fifth long-lived district in the world. Surface hydrophobicity and adherence capability to intestinal epithelial cells in vitro of bifidobacteria were simultaneously investigated for the first time. It has been demonstrated that all the strains exhibited adhesive properties to some extent using intestinal Caco-2 cell line in in vitro model. It could be conclude that the higher hydrophobic strains the stronger adhesive capability. The highest value of hydrophobicity (37.24+/-1.45% and 32.06+/-1.21%) was obtained for strains H-10 and I-6, respectively; correspondingly, the strongest adherence ability (49.47+/-4.88/cell and 47.33+/-2.72/cell) was achieved, respectively. Correlation between surface hydrophobicity and adherence ability of different Bifidobacterium strains including polynomial regression equation (R2=0.78) had been achieved. The present study provided a liable and effective method for screening bifidobacteria with the ability to adhere to intestinal epithelial cells.     

Cell-surface hydrophobicity and scum formation of Rhodococcus rhodochrous strains with different colonial morphologies

Rhodococcus rhodochrous has been reported to be one of the micro-organisms responsible for the formation of scum which is thick and viscous biological foam in activated sludge plants. The hydrophobicity of mycolic acids present on the cell surface and the long-branched shape of the hyphae have been thought to contribute to the scum formation. Cell surface hydrophobicity and scum formation of four R. rhodochrous strains with different colony morphologies were determined, and the results showed that the two rough strains had strong cell surface hydrophobicity and produced scum, whereas the weakly hydrophobic smooth strain and the hydrophilic mucoidal strain did not. All four strains displayed long, branched hyphae, and their electrophoretic mobilities were similar, between pH 4 and 9. These data suggest that changes in the cell surface hydrophobicity of the R. rhodochrous result in changes in the culture characteristics and the formation of scum.     

Toxin profiles, and cell-surface properties of Salmonella strains isolated from Swedish travelers.

Toxin production, cell-surface hydrophobicity and fibronectin-binding properties of 21 Salmonella strains of different species, isolated from Swedish travelers to different parts of the world, were studied. Cell sonicate supernatants from blood agar grown cultures of 80% of the strains induced rabbit skin permeability reaction in the form of induration and/or blueing while 33% of the strains also produced cell necrotizing factor on rabbit skin. Four strains were negative in the rabbit skin permeability test, while only two were negative when tested on CHO cells. When cultured on blood agar, a majority of the strains (17/21) showed low cell-surface hydrophobicity, showing no aggregation even at 1.5 M ammonium sulfate concentration in salt aggregation test (SAT), while only four strains showed high cell-surface hydrophobicity. Furthermore, these strains could be classified as low fibronectin binders due to their poor interaction with fibronectin or its 29 kDa N-terminal fragment.     

Hydrophobicity of Fusobacterium necrophorum biovars A and B

Abstract Biovar A strains of Fusobacterium necrophorum exhibited high hydrophobicity when examined by the method of Rosenberg et al. Biovar B strains showed a lower cell surface hydrophobicity than biovar A strains. Biovar B strains were divided into 2 groups according to their hydrophobic activity. The strains of biovar A and the first group of biovar B were increasingly removed from aqueous phase to octane phase by increasing the volume of octane, but the turbidity of the second group of biovar B was not significantly affected. The hydrophobicity of biovar A strains decreased on heating at 60 and 100°C for 30 min.