Partition of Salmonella typhimurium in a two-polymer acqueous phase system in relation to liability to phagocytosis

The influence of different concentrations of melatonin on the cell surface hydrophobic characteristics of Neisseria meningitidis

The cell surface hydrophobicity of micro-organisms is a characteristic that has been associated with the colonization of mammalian epithelia and with their capacity to induce diseases. Melatonin is a hormone produced by the pineal gland that affects the immune response mechanism. This study investigated, as an expression of the virulence of Neisseria meningitidis, how its hydrophobic characteristics were affected by exposure to increasing concentrations of melatonin. An increase in the cell surface hydrophobicity of N. meningitidis was found at concentrations of 1 mmol l(-1), while lower concentrations of melatonin did not significantly affect this particular cell surface characteristic of the micro-organism. It may be concluded that melatonin clearly influences the cell surface hydrophobicity of N. meningitidis, a circumstance that should be taken into account in future studies to determine whether this hormone plays a role in the variable pathogenicity of the bacteria in different hosts.

Physical chemical description of bacterial adhesion

For the description of general bacterial adhesion phenomena two different physicochemical approaches are available. The first one, based on a surface Gibbs energy balance, assumes intimate contact between the interacting surfaces. According to this approach adhesion is solely related to the Gibbs energies of the surfaces involved. The second approach, based on colloid chemical theories (DLVO theory), allows for two types of adhesion: 1. secondary minimum adhesion, which is often weak and reversible, and 2. irreversible primary minimum adhesion. In the first case a thin water film is present between the interacting surfaces. In the DLVO approach adhesion is determined by long range interactions, i.e., Van der Waals and electrostatic interactions. Van der Waals interactions may be related to the hydrophobicity of the cell wall. For the measurement of bacterial hydrophobicity and electrokinetic potential several macroscopic methods are available. Based on a literature review of the influence of both surface characteristics on adhesion, it is concluded that the surface Gibbs energy balance approach is not adequate to describe the majority of adhesion phenomena. On the other hand the DLVO-theory describes the observations fairly well, especially in the case of reversible (secondary minimum) adhesion. The influence of adsorbing (in)organic compounds, extracellular polymers and cell surface appendages on adhesion can also be predicted by a DLVO-type approach.

Surface charge and hydrophobicity of Campylobacter jejuni strains in relation to adhesion to epithelial HT-29 cells

Hydrophobicity and surface charge of clinical isolates of Campylobacter jejuni strains were investigated by aqueous two-phase partitioning (one-step and counter-current distribution), ion exchange chromatography and hydrophobic interaction chromatography. There was a good correlation between the different physico-chemical methods reflecting the same bacterial property. All strains were negatively charged and exposed a hydrophobic surface, but to a varying extent. Bacteria with a high negative surface charge and a weak hydrophobic surface adhered better to human intestinal HT-29 cells than strains with less charge and a more hydrophobic surface. Highest adhesion was shown by a strain differing from all the others in charge properties. It was also found that the tendency to aggregate was higher among the strains showing the greatest degree of adherence.

Mannose-specific and hydrophobic interaction between Escherichia coli and polymorphonuclear leukocytes--influence of bacterial culture period

The influence of culture period on mannose-specific and hydrophobic properties of the bacterial surface and on bacteria/polymorphonuclear leukocyte (PMNL) interaction was studied. Four E. coli strains, PN7 (01:K1), ABU2 (ON:K14), CU9 (06:K14) and CU13 (08:KN) and two Salmonella typhimurium strains 395 MR10 and 395 MS, well characterized according to physicochemical surface properties, presence of type 1 fimbriae and interaction with PMNL, were used in the study. The results show that with prolonged culture period, the liability to hydrophobic interaction increases, the agglutination-strength of mannose-specific maltobionamide liposomes increases, while the agglutination-titer with guinea-pig erythrocytes remains constant. Furthermore, the mannose-specific association with and metabolic activation of PMNL is augmented, while the ingestion is unchanged. In addition, our results demonstrate differences in sensitivity between the methods used to detect exposure of mannose-specific structures on the surface of bacteria, and that the culture condition is important for bacterial surface properties. It thus appears that the culture conditions have a great influence on the surface properties of E. coli bacteria and the interaction with phagocytic cells.

Relationship between ultrastructure and specific functions of macrophages

The main function of the macrophages, which is to ingest and degrade any foreign molecules or particles penetrating the organism, appears in the development of the different structures implicated in endocytic activity. The macrophage's high endocytic property first appears in its irregular shape and the large number of extensions of the cell membrane, allowing the rapid capture of extra-cellular material. Adhesion between macrophage cell surface and molecules or particles is greatly enhanced by the presence of varied kinds of receptors: lectin-like receptors which bind specific sugars or highly specific receptors such as Fc and C3b receptors, which increase phagocytosis of opsonized microbes. The microbicidal properties reside in part in the production of superoxide anions which result from the activity of a NAD(P)H oxidase. This enzyme is located in the plasma membrane. Its activity could be demonstrated with a cytochemical method, on the cell surface and along the phagosome membrane. It is, however, very weak in resident macrophages and increases after stimulation or activation. The second kind of bactericidal property corresponds to cationic proteins located in lysosomes. After fusion between lysosomes and phagosomes, they contribute to microbe killing by permeabilizing microbe envelopes. Lysosomes, which contain diverse acid hydrolases and are responsible for the degradation of ingested material, play a crucial role in macrophage endocytic activity. Their number increases in parallel with endocytic activity during macrophage differentiation and is particularly high after ingestion of degradable material. Contrary to polymorphonuclear leukocytes, macrophage is very poor in granules containing peroxidase. The latter, which are rather abundant in monocytes, disappear during macrophage maturation. They do not seem thus to be implicated in macrophage microbicidal activity. Endocytosis is accompanied by rapid and intense exchanges between the different membrane compartments of the cell (plasma membrane, pinosomes or phagosomes, endosomes, lysosomes, Golgi apparatus, etc.). These exchanges seem to occur by transitory fusions between vesicles coming from different compartments, rapidly followed by their recycling to their original compartment. This system of membrane shuttle has been clearly observed after formation of phagosomes or pinosomes in which the internalized plasma membrane is recycled back to the cell surface within a few minutes after their formation. This membrane traffic is especially intense in macrophages, the endocytic activity of which is very high, but it also exists in all cell types.(ABSTRACT TRUNCATED AT 400 WORDS)

Activation of polymorphonuclear leukocytes by salmonella

The interaction of polymorphonuclear leukocytes (PMN) with salmonella, as studied by chemiluminescence and phagocytosis, was very different for a number of clinical isolates. Particularly bacteria in the serogroups C1 and E4 deviated from other Salmonella. The differences were observed in the rate of activation, peak value, duration of the chemiluminescence, and in the extent of association and ingestion as studied microscopically. Old laboratory S-strains such as Salmonella typhimurium 395 MS and S. minnesota S99 , which did not associate with the PMN, showed little activation of the PMN, whereas their phagocytosis-sensitive R-mutants induced rapid activation, high peak values, and short duration of the chemiluminescence. Certain isolates belonging to the C1/E4 group induced intermediate types of reactions. The kinetics of the activation was related to the physicochemical surface properties of the bacteria. Heating the bacteria at 70 degrees C for 45 min enhanced the activation of PMN by the S-type strains conspicuously but in different ways, whereas that of R-mutants was delayed. Different clinical isolates of salmonella have shown different physico-chemical surfaces, liability to phagocytosis by PMNs and different degrees of eliciting inflammatory mediators from PMNs in vitro. The results indicate that the C1/E4 group of Salmonella has pathogenicity mechanisms different from most salmonellae.

Surface characteristics of group A streptococci with and without M-protein

Twenty M protein-positive and eight M protein-negative strains of group A streptococci were investigated with respect to surface hydrophobicity and amount of lipoteichoic acid (LTA). Surface hydrophobicity as determined in polymer two-phase systems varied substantially between individual strains and there was no correlation to the presence of antiphagocytic M protein. The amount of LTA on the surface of the bacteria varied with hydrophobic affinity of the cells. Strains with a high content of surface LTA were found among both M-positive and M-negative streptococci. Cellular and extracellular LTA was estimated on six strains by the ability of hot phenol extracts and culture fluids to sensitize erythrocytes and by rocket immunoelectrophoretic quantitation. Differences in content of surface LTA did not correlate to differences in the total amount of cellular LTA. Pepsin digestion of M-positive group A streptococci at suboptimal pH resulted in a loss of M antigen whereas surface LTA and the hydrophobic interaction liability was retained. The results indicate that the degree of surface hydrophobicity as measured by two-phase partitioning is not correlated to either the type-specific or the antiphagocytic moiety of M protein. The results support the correlation between surface LTA and surface hydrophobicity of group A streptococci.

Lipoteichoic acid is the major cell wall component responsible for surface hydrophobicity of group A streptococci

The contribution of lipoteichoic acid (LTA) to the hydrophobic surface properties of group A streptococci was investigated in aqueous dextran-polyethylene glycol two-phase systems. Enzymatic digestions were performed to characterize the hydrophobic surface structure. The results obtained indicated that LTA is a major factor responsible for the hydrophobic character of the cell surface of group A streptococci. This was further supported by the similarity of partition in polymer two-phase systems between whole group A streptococci and tritiated LTA extracted from a group A streptococcal strain. Surface LTA was also determined on intact organisms by a new method measuring the adsorption of antibodies to LTA to the bacterial surface. A correlation was found between the content of surface LTA and the hydrophobicity of the group A streptococci. We conclude that surface-associated LTA is the major factor determining surface hydrophobicity of group A streptococci.

Physicochemical and functional changes in human leukemic cell line HL-60

The recently established human promyelocytic cell line HL-60 was induced to differentiate in the present of DMSO. During this process, physicochemical, and functional changes were detected simultaneously. After exposure to DMSO for more than 1 day, the cell volume decreased and the tendency for hydrophobic interaction increased. Using a hydrophobic two-phase system in counter current distribution fashion, it was then possible to separate more mature metamyelocytes and segmented granulocytes from immature myeloblasts and promyelocytes. Increased functional maturity was reflected by increased chemiluminescence (CL) response and phagocytic activity. Using yeast particles opsonized with IgG as stimulating agent, the CL response increased already after 1 day in DMSO, in parallel with increased phagocytosis of these particles. In contrast, C3b-opsonized yeast and phorbol 12-myristate 13-acetate (PMA) did not enhance the CL response conspicuosly until days 3-4. These data suggest that Fc receptor function linked to phagocytosis and the activation of oxidative metabolism develop earlier than that of C3b and PMA. The dissociation between Fc- and PMA-dependent stimulation of the oxidative metabolism may reflect different mechanisms of activation.

Isoelectric points and surface hydrophobicity of Gram-positive cocci as determined by cross-partition and hydrophobic affinity partition in aqueous two-phase systems

Thirty-nine streptococcal strains belonging to groups A, C, and G and 12 staphylococcal strains were investigated with respect to surface charge and hydrophobicity. Isoelectric points of the bacteria were determined by cross-partition experiments in dextran-polyethylene glycol two-phase systems containing charged polymers. The results obtained indicate that group A, C, and G streptococci have isoelectric points of pH 3.75 +/- 0.15 standard deviation. Staphylococci show an isoelectric point of around pH 2 and thereby differ markedly from the streptococci. Pretreatment of bacteria with human serum resulted in a significant change in the isoelectric points of streptococci. In a second series of experiments, an aqueous dextran-polyethylene glycol two-phase system containing polyethylene glycol palmitate or stearate was used to study the hydrophobic surface properties of the bacterial cells. The partition of the staphylococci was not influenced by the addition of up to 1% (wt/wt) polyethylene glycol palmitate or stearate, whereas the streptococci showed a large variation in affinity for polyethylene glycol-bound hydrophobic groups. The bacterial strains included in the study were also tested for uptake of human serum proteins. A positive correlation was found between the hydrophobic affinity of group A streptococci and the density of receptors for aggregated beta-2-microglobulin.

Mucosal barrier mechanisms. Interplay between secretory IgA (SIgA), IgG and mucins on the surface properties and association of salmonellae with intestine and granulocytes

Rough Salmonella typhimurium 395 MR 10 bacteria sensitized with SIgA were used to assess the effect of secretory IgA (SIgA) on bacterial association with the intestine of rat and with a column of hog gastric mucin, and on IgG-mediated surface properties and interaction with polymorphonuclear leucocytes. It was found that SIgA increased the affinity for mucus belt of the intestine and for the mucin column, but reduced IgG-enhanced phagocytosis and surface hydrophobicity and charge of the bacteria. It is suggested that the ability of SIgA to render bacteria mucophilic and to modify IgG-mediated reactions serve the purpose of secluding bacteria from contact with mucosal membranes and depress inflammatory reactions at the site of infection.

A new test based on 'salting out' to measure relative surface hydrophobicity of bacterial cells

A simple method for quantification of the hydrophobic surface properties of bacteria is described. The method is based on precipitation of cells by salts, for instance (NH4)2SO4. The order in which cells are precipitated is a measure of their surface hydrophobicities, the most hydrophobic cells being first precipitated at low salt concentration. Temperature, pH, time and the bacterial cell concentration were shown to affect the results. When these variables were kept constant the method was highly reproducible. This 'salting out' method was applied to enterotoxigenic Escherichia coli strains with different surface protein antigens (fimbriae, fibrillae and colonization factor antigen, CFA). These enterotoxigenic E. coli strains were found to have surface hydrophobicity in the following order: CFA/I greater than CFA/II greater than K88 similar to K99 greater than type 1.

Effect of specific binding of human albumin, fibrinogen, and immunoglobulin G on surface characteristics of bacterial strains as revealed by partition experiments in polymer phase systems

Four strains of gram-positive cocci with different combinations of positive binding of human proteins were investigated with respect to changes in physicochemical surface properties after specific protein binding. Staphylococcus aureus Cowan I, two group A beta-hemolytic streptococci, and one group G streptococcal strain were studied; they represented three different combinations of reactivity for human serum albumin, human immunoglobulin G, and fibrinogen. Using single-tube partition of bacterial cells in a dextran-polyethylene glycol system of constant polymer concentration but varying ionic compositions, it was possible to detect changes in the partition of bacteria after specific protein binding. There was a correlation between the binding of radiolabled human proteins to the bacterial strains and the effect of human proteins on the partition of the bacteria in the phase systems. Thus, the specific binding of proteins to the bacteria changes their physicochemical surface properties. These types of bacteria-protein interactions may play an important role in modulating host-parasite relationships.

Association with HeLa cells of LPS mutants of Salmonella typhimurium and Salmonella minnesota in relation to their physicochemical surface properties

Different LPS mutants of Salmonella typhimurium and Salmonella minnesota have been investigated with respect to (1) their tendency to associate with HeLa cell monolayers, and (2) their physicochemical surface properties. Aqueous biphasic partitioning, hydrophobic interaction chromatography, and ion exchange chromatography have been used to characterize the bacterial cell surface properties with respect to charge and hydrophobicity. Liability to hydrophobic interaction was defined either by the change of partition in a dextran-polyethylene-glycol (PEG) system by the addition of PEG-palmitate (P-PEG), or by the elution pattern from Octyl-Sepharose. Accordingly, charge was asssessed by the effect of positively charged trimethylamino-PEG (TMA-PEG) on the partition, and by the elution from DEAE-Sephacel. Bacterial being negatively charged and liable to hydrophobic interaction had the highest tendency to associate with HeLa cells. In some cases the methods for surface analysis gave conflicting results on charge and/or liability to hydrophobic interaction of the same LPS mutant. Possible reasons for these differences and the role of bacterial cell surface structures contributing to physicochemical character are discussed.

Mannose-binding activity of Escherichia coli: a determinant of attachment and ingestion of the bacteria by macrophages

Recently, it was suggested that a mannose-specific lectin on the bacterial cell surface is responsible for the recognition by phagocytic cells of certain nonopsonized Escherichia coli strains. In this study we assessed the interaction of two strains of E. coli at different phases of growth with a monolayer of mouse peritoneal macrophages and developed a direct method with [(14)C]mannan to quantitate the bacterial mannose-binding activity. Normal-sized bacteria were obtained from logarithmic and stationary phases of growth. Nonseptated filamentous cells were formed by growing the organisms in the presence of cephalexin or at a restrictive temperature. Attachment to macrophages of all bacterial forms was inhibited by methyl alpha-d-mannoside and mannan but not by other sugars tested. The attachment of stationary phase and filamentous bacteria to macrophages, as well as their mannose-binding activity, was similar, whereas in the exponential-phase bacteria they were markedly reduced. The results show a linear relation between the two parameters (R = 0.98, P < 0.001). The internalization of the filamentous cells attached to macrophages during 45 min of incubation was much less efficient (20%) compared to that of exponential-phase, stationary-phase, or antibody-coated filamentous bacteria (90%). The results indicate that the mannose-binding activity of E. coli determines the recognition of the organisms by phagocytes. They further suggest that administration of beta-lactam antibiotics may impair elimination of certain pathogenic bacteria by inducing the formation of filaments which are inefficiently internalized by the host's phagocytic cells.

Surface properties of Chlamydia psittaci

The surface properties of elementary bodies of Chlamydia psittaci were investigated by diethylaminoethyl-Sephadex chromatography, cytophoresis, partitioning in an aqueous polymer two-phase system, and hydrophobic interaction chromatography of the organism. The surface of C. psittaci was found to be hydrophobic and negatively charged at pH 7 and to have an isoelectric point of about pH 5. Reagents which block free carboxyl groups altered the surface charge of C. psittaci and caused the organism to agglomerate. The possible significance of hydrophobicity and surface charge on the ingestion of C. psittaci by host cells is discussed.

Influence of O and K antigens on the surface properties of Escherichia coli in relation to phagocytosis

Strains of Escherichia coli with different O and K antigens were investigated with respect to physicochemical surface characteristics and liability to phagocytosis. Using two-phase partitioning analysis for the surface characterization, three main groups of strains emerged: Group I (O1:K1, O2:K1, O3:K2ab) showing both smooth hydrophilic O antigens and negatively-charged K antigen which rendered the strains maximally resistant to phagocytosis. Group II (O55:K59, O111:K58) showed no acidic K antigen but only smooth hydrophilic O antigen properties. However, these strains were as resistant to phagocytosis as the strains in group I. A third group (O14:K7, O24:K +) contained strains with rough, hydrophobic O antigen and negatively-charged K antigen. When the K antigen was removed by heat treatment these strains became more sensitive to phagocytosis. Certain other strains (O28:K-, O56:K + and O118:K-) did not fit into the three groups. These experiments show that the physicochemical surface effects and biological significance of the K antigen must be evaluated in relation to the properties conveyed by the corresponding O antigens.

Surface characteristics of Escherichia coli strains in relation to development of bacteraemia

Three groups of E. coli bacteria isolated from blood, urine and faeces were analysed with respect to physicochemical surface properties in aqueous polymer two-phase systems. Eighty-eight per cent of the bacteria isolated from blood cultures showed affinity for the dextran-rich bottom phase, whereas 60% and 30% of the bacteria isolated from urine and faeces, respectively, collected to the same phase. Further two-phase analysis indicated that the bacteraemia strains exposed more negative surface than the other groups of bacteria, and that this charge was reduced after heat treatment (70 degrees C, 40 min). These results thus indicate that the strains causing bacteraemia possess similar surface properties, and may have been selected from the more heterogeneous group of bacteria found in urine and faeces. It is further conceivable to propose that bacteria found in the blood expose more heatsensitive, negatively-charged K antigen than the other groups of bacteria.

Reduction of phagocytosis, surface hydrophobicity and charge of Salmonella typhimurium 395 MR10 by reaction with secretory IgA (SIgA)

Binding of human colostral secretory IgA (SIgA) to Salmonella typhimurium 395 MR10 decreased the liability to hydrophobic interaction of the bacteria, as analysed by hydrophobic interaction chromatography on Octyl-Sepharose and partition in an aqueous polymer two-phase system consisting of dextran, poly(ethyleneglycol) (PEG) and poly-(ethyleneglycol)-palmitate (P--PEG). SIgA also reduced the negative charge of the bacteria. Treatment of the bacteria with centrifuged but not further fractionated colostrum added positive charge to the bacteria which was removed by treatment with pepsin. Colostral SIgA reduced the in vitro phagocytosis of S. typhimurium MR10 by polymorphonuclear leucocytes. The adhesion of the bacteria to cellulose membrane filters in the absence of phagocytes was also reduced after the interaction with SIgA. It is proposed that the binding of SIgA to bacterial surfaces has hydrophilic and anti-adhesive effects, which may serve to exclude antigen from mucosal surfaces.

Ultrastructural studies on the interaction between Salmonella typhimurium 395 M and HeLa cells

The interaction of Salmonella typhimurium 395 MS and its rough Rd-mutant 395 MR10 with HeLa cells was studied by transmission and scanning electron microscopy. The bacteria attached to central as well as more marginal positions of the HeLa cell surface. Bacteria associated preferentially to HeLa cells with a relatively low number of microvilli, in which they often were entangled. Bacteria attached to the cell border were sometimes surrounded by membrane folds, possibly as a response to their attachment. Infected cells had longer and more slender microvilli compared with noninfected cells. Some parts of the attached bacteria were in close contact with the HeLa cell membrane, whereas other parts were separated from the latter by a gap. Bacteria adhered preferentially to microvilli without obvious membrane damage. Most of the intracellular bacteria were surrounded by a membrane, often appearing as a vacuole, which sometimes contained more than one bacterium. Intracellular bacteria seemed to be morphologically intact. We propose that S. typhimurium enter HeLa cells by a process of phagocytosis.

Differences in hydrophobic surface characteristics of porcine enteropathogenic Escherichia coli with or without K88 antigen as revealed by hydrophobic interaction chromatography

Porcine enteropathogenic Escherichia coli strains possessing or lacking K88 antigen were studied by using hydrophobic interaction chromatography on cross-linked agarose gels with alkyl or aryl substituents (amphiphilic gels) to determine whether or not they possessed surface-associated hydrophobic properties. Strains with K88ab or K88ac antigen adsorbed to phenyl and octyl Sepharose gels in the presence of 4 M sodium chloride. This property correlated with phenotypic expression of K88 antigen. Cells grown at 37 degrees C but not those grown at 18 degrees C possessed hydrophobic adsorptive characteristics in addition to the property of mannose-resistant hemagglutination of guinea pig erythrocytes. Adsorption of K88-positive strains to gels with hydrophobic ligands was independent of O group and enterotoxicity. Strains lacking K88 antigen did not adsorb to the hydrophobically substituted derivatives of Sepharose and lacked mannose-resistant hemagglutinating characteristics. Neither the presence of additional polysaccharide K antigens nor nonhemagglutinating pili conferred the property of hydrophobic interaction on the strains. K88-positive bacteria had a lower electrophoretic migration rate than did K88-negative bacteria of the same serotype in free-zone electrophoresis. K88-positive bacteria also adsorbed strongly to hydrophobic ligands in the presence of 1 M ammonium sulfate, whereas K88-negative strains did not. These observations provide evidence for the suspected role of hydrophobic interaction in the adhesive properties of certain enteropathogenic strains of E. coli. Moreover, hydrophobic interaction chromatography provides convenient and rapid alternative means of screening strains for a property potentially associated with adhesiveness.

The effect of colostrum and colostral antibody SIgA on the physico-chemical properties and phagocytosis of Escherichia coli o86

A hydrophilic effect of human colostrum and colostral antibody SIgA binding on Escherichia coli o86 has been demonstrated by hydrophobic interaction chromatography on Octyl-Sepharose and partition in a polymer two-phase system containing dextran, poly(ethyleneglycol) and poly(ethyleneglycol)-palmitate. Furthermore, antibody SIgA binding reduced the negative surface charge of the E. coli bacteria. The reaction between centrifuged but not further purified colostrum and bacteria yielded a complex which, compared to bacteria alone, showed decreased negative and increased positive surface charges, the latter being sensitive to pepsin. Binding of SIgA or colostrum to E. coli showed no definite effect on the attachment to and phagocytosis by polymorphonuclear cells in vitro. The effects observed are discussed in relation to the structure of SIgA.

Association of some enterobacteria with the intestinal mucosa of mouse in relation to their partition in aqueous polymer two-phase systems

The association of enterobacteria with mouse intestinal mucosa has been investigated by pumping heat-killed, radioactively-labelled bacteria through the gut lumen in vitro. Approximately 20 cm of the small intestine proximal to the ileo-caecal valve was rinsed, excised and maintained in an organ bath. By using two different bacteria labelled with different radioactive isotopes, the relative association of the two bacterial pumped through the same piece of gut was determined. Cross-labelling showed that choice of isotope did not affect the association. Salmonella typhimurium 395 MR10 was used as reference and the other bacteria investigated related to it. S. typhimurium MR10 and Escherichia coli O 14 K7, which are relatively lipophilic, showed greater association than S. typhimurium 395 MS and E. coli O 111 K58, which are more hydrophilic. Prolonged incubation of bacteria with the length of intestine in vitro leading to damage of the brush border of the mucosal epithelium enhanced the association of the bacteria. These data suggest that similar physico-chemical surface properies govern the association certain enterobacteria to the intestinal mucosa as in phagocytosis with professional phagocytes.

Surface-charge characteristics of smooth and rough Salmonella typhimurium bacteria determined by aqueous two-phase partitioning and free zones electrophoresis

Aqueous biphasic partitioning of Salmonella typhimurium S and R bacteria in a system containing 6.2 per cent (w/w) dextran 500 and 4.4 per cent (w/w) poly(ethyleneglycol) 6000 (PEG) was similar to the partition of the corresponding surface lipopolysaccharide (LPS). Further partition analysis with charged PEG showed that S bacteria and their LPS exposed very little charge, whereas R bacteria and their LPS showed a conspicuous negative charge at neutral pH. Free zone electrophoresis also indicated that the S bacteria have a much lower surface charge density than the R bacteria and accordingly a different surface structure. Thus, the physico-chemical properties of the bacterial surface seem to be determined to a great extent by the characteristics of the cell surface LPS.

Infection of HeLa cells with Salmonella typhimurium 395 MS and MR10 bacteria

After interaction with HeLa cells cultured in vitro, the fraction of adhering extracellular and that of internalized smooth Salmonella typhimurium 395 MS and rough 395 MR10 have been determined by two different techniques. (i) By using the indirect fluorescent-antibody technique on unfixed and acetone-fixed HeLa cell preparations, intracellular bacteria were considered to become stained only after acetone fixation. (ii) Based on the assumption that gentamicin affects only extracellular bacteria, disintegration of the infected HeLa cells and viable count allowed the determination of internalized bacteria. Both techniques showed that MS as well as MR10 bacteria gained intracellular access, the fraction of MR10 cells doing so being much greater. The net increase in the intracellular bacterial population was small within 3 h of incubation.

The tendency of smooth and rough Salmonella typhimurium bacteria and lipopolysaccharide to hydrophobic and ionic interaction, as studied in aqueous polymer two-phase systems

In aqueous two-phase system, the partition of bacteria and lipopolysaccharide from a rough (R) strain (Rd-mutant) of Salmonella typhimurium is influenced by polymers with covalently linked hydrophobic groups indicating hydrophobic structures accessible at the cell surface. Furthermore, the partition of the R bacteria is influenced by a number of inorganic positive and negative ions, presumably as a consequence of interaction with negatively charged surface structures. In contrast, smooth (S) bacteria and lipopolysaccharide from the parent strain do not seem to participate in either hydrophobic or charge interaction indicating extensive hydrophilicity without charge. Thus, the S-specific polysaccharide side chain of S. typhimurium might serve the purpose of blindfolding aspecific host defence mechanisms dependent on hydrophobicity and charge. On the contrary, the R bacteria and R lipopolysaccharide have physico-chemical properties which predispose to interaction with several types of cells, organelles and molecules.

Physiochemical consequences of opsonization of Salmonella typhimurium with hyperimmune IgG and complement

Partition in an aqueous, two-polymer phase system containing dextran and polyethylene glycol was employed to investigate the physico-chemical changes inflicted upon the cell surface of a smooth strain of Salmonella typhimurium by the binding of antibody IgG and complement. The minimum antibody concentration for increased phagocytosis in vitro was approximately the same as that for a significant change in two-phase partition, ca 8000 mol/bacterium, whereas a lower concentration, less than 4000 mol/bacterium, was sufficient to increase clearance in vivo. After pepsin digestion of IgG, larger quantities, ca 35,000 mol/bacterium, was required for opsonization and to influence two-phase partition. Addition of normal rabbit or guinea-pig serum to bacteria sensitized with a low concentration of antibody IgG conspicuously enhanced phagocytosis and affinity for the dextran-rich phase. The results show that binding of 8000 IgG antibody molecules or more to smooth S. typhimurium generates physicochemical changes of the bacterial surface which from studies on S leads to R mutations are known to correlate with hydrophobicity, negative charge and phagocytosis. Such results support the view that one important function of IgG antibody and complement is to decrease the hydrophilic properties of the bacteria which is thought to be a prerequisite for phagocytosis.

Association of viable and inactivated Salmonella typhimurium 395 MS and MR 10 with HeLa cells

The mouse-virulent Salmonella typhimurium 395 MS, containing a complete lipopolysaccharide (LPS) structure with S-specific repeating units, and the nonvirulent, LPS-defective mutant 395 MR 10 (chemotype Rd), derived from it, were studied for their tendency to interact with HeLa cells. In the definition of interaction no distinction has been made between intracellular and cell membrane-attached bacteria. R10 bacteria were found to have a greater tendency to interact than MS bacteria. This difference was seen as early as 1 h after the start of incubation, but it became more pronounced beyond 3 h. Heat-killed and ultraviolet-killed R10 bacteria interacted with HeLa cells less than living ones. Killed MS bacteria interacted to an extent similar to that of living ones. These results are discussed in relation to the susceptibility of the bacteria to phagocytosis by professional phagocytic cells and to the physiochemical properties of the bacteria as measured by their distribution in a two-polymer, aqueous-phase system.

On the physical-chemical effect of colostral antibody binding to Escherichia coli O 86

Sensitization of Escherichia coli O 86 with colostrum or purified colostral sIgA antibody produces a physical-chemical change of the bacterial surface detectable as a change in partition in dextran-polyethylene glycol polymer two-phase systems. Sensitization with colostrum or sIgA reduces affinity for the dextran-rich phase. In contrast immune serum, IgG and complement increase the affinity for that phase. The results are compatible with the hypothesis that hydrophilic particles, e.g. certain strains of bacteria, are less liable to attachment to and phagocytosis by animal cells than hydrophobic particles, e.g. other bacterial strains. Sensitization with secretory IgA enhances the hydrophilicity thereby making possible an escape mechanism operating at the mucosal surfaces.

Influence of hyperimmune immunoglobulin G on the physicochemical properties of the surface of Salmonella typhimurium 395 MS in relation to interaction with phagocytic cells

Partition in an aqueous, two-polymer phase system containing dextran and polyethylene glycol was employed to investigate the physicochemical changes inflicted by the presence of immunoglobulin G (IgG) antibodies on the cell surface of a smooth strain of Salmonella typhimurium. Adding increasing amounts of anti-Salmonella IgG to the bacteria decreased the affinity for the polyethylene glycol-rich top phase, with a concomitant increase in in vivo clearance and in vitro phagocytosis by rabbit polymorphonuclear cells. Similarly, S --> R mutations in the same S. typhimurium strain decrease the affinity for the top phase and increase the liability to phagocytosis. The limiting antibody concentration to demonstrate increase of in vitro phagocytosis was approximately the same as that to produce a significant effect in the phase system, whereas lower concentrations were needed to increase the in vivo clearance. The results show that adsorption of IgG antibodies to bacteria brings about physicochemical changes of the cell surface which seem to promote the phagocytosis by polymorphonuclear cells and uptake in the reticuloendothelial system.