Characterization of mutants of Salmonella typhimurium by counter-current distribution in an aqueous two-polymer phase system

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.

Physico-chemical surface properties of Shigella sonnei

In partition in two-phase systems as well as in hydrophobic and ion exchange chromatography a number of Sh. sonnei isolates with different phage patterns showed similar physico-chemical surface properties. All the isolates displayed hydrophobicity and a small negative charge. In this way the shigellae were different from salmonella S-strains and E. coli strains associated with infantile diarrhoea which have shown hydrophilic properties and nearly no charge. They were also different from E. coli strains with typical K-antigen often grown from patients with septicemia and upper urinary tract infection, which have shown hydrophilic properties and a great negative charge. However, the Sh. sonnei isolates were similar to E. coli strains belonging to certain serogroups which have been grown from patients with dysentery-like diseases. The results indicate that physico-chemical surface properties are related among enterobacteria belonging to different genera which have been grown from similar types of infections.

Anionic sites on the envelope of Salmonella typhimurium mapped with cationized ferritin

Binding of either ferritin (F) or cationized ferritin (CF) was employed to indicate the surface charge of the envelope of mainly two Salmonella typhimurium strains (395 MR10, a Rd-mutant, and LT2-M1, a UDP-galactose-4-epimerase-less mutant). Lowering the pH from 7 to 4 decreased binding of CF, but increased binding of F. At low concentrations, the distribution of CF on S. typhimurium 395 MR10 was in general random, with individual ferritin molecules often forming clusters of two or three particles. At ionic strengths of 0.25M NaCl, ferritin produced distinctive, larger clusters at relatively few sites (10-50/cell). Addition of galactose to cultures of growing S. typhimurium, LT2-M1 reduced the binding of CF in 1-10 min, and numerous ferritin-free areas became visible. Possibly this is caused by a pluri-focal reduction in the negative cell surface charge that was generated at the multiple sites of export of new, smooth-type lipopolysaccharide, which either exhibits lesser charge or masks a preexisting surface charge. Dividing cells may show unequal charges on the prospective daughter cells, and the difference in the capacity for ferritin adsorption of both daughter cells is sharply separated at the division site.

Determination of the surface tension of biological cells using the freezing front technique

The freezing front technique for solid surface tension measurements was used to obtain the surface tensions of glutaraldehyde-fixed human erythrocytes, and fresh human lymphocytes and granulocytes in aqueous media. The results agree well with the values obtained by other methods and indicate that the freezing front technique is sufficiently sensitive to detect small differences (of the order of 0.1 ergs/cm2) in surface tension. This property, along with a number of applications for which it is uniquely suited, makes the freezing front technique an important new approach to the measurement of the surface tensions of biological cells and of small particles in general.

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.

Ionic interaction of oral streptococcal bacteria studied by partition in an aqueous polymer two-phase system

The net surface charge of various oral streptococci were assessed by aqueous two-phase partitioning in a dextran-polyethylene glycol system. Great variability was found among individual strains within all species tested. Type 1 strains of Streptococcus sanguis serotypes which have been found to be more adherent, exposed a lower negative net surface charge than Type 2 strains.

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.

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.

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.

Phagocytosis as a surface phenomenon. V. Contact angles and phagocytosis of rough and smooth strains of Salmonella typhimurium, and the influence of specific antiserum

The angle made by a drop of saline in contact with a monolayer of Salmonella typhimurium or phagocytic cells, the contact angle, is a measure of their relative interfacial tension, and is predictive of a successful phagocytosis. Smooth strains of S. typhimurium possess a contact angle lower than the phagocytic cells and resist phagocytosis. Rough strains have an angle higher than the phagocytes and are readily engulfed. The lower contact angle of smooth strains can be increased by treatment with specific antibody resulting in more efficient phagocytosis.

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.

Separation of erythromycin-resistant and -susceptible subpopulations of Escherichia coli 15 by partition in two-polymer aqueous phases

Partition of cells in two-polymer aqueous phases depends on subtle differences in the cells' surface properties (primarily surface charge). A culture of Escherichia coli 15 arg(-) was subjected to countercurrent distribution in a dextranpolyethylene glycol aqueous phase system and found to consist of two well-differentiated subpopulations. Clones derived from these two subpopulations (designated clones 5 and 6) exhibited characteristic partitions and were stable on subculture. Clone 5 cells were found to be susceptible to erythromycin and clone 6 cells were resistant. When a culture of clone 5 was exposed to erythromycin, resistant mutants were selected with the same partition as clone 6. Countercurrent distribution in two-polymer aqueous phase systems is thus shown to be a sensitive method for detecting some heterogeneities of bacterial populations and resolving such mixtures. Possible clinical implications of changes in bacterial surface properties associated with acquired drug resistance are discussed.

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

Analysis of the partition in a two-polymer phase system of Salmonella typhimurium R mutants with different susceptibility to phagocytosis distinguished between the mutants. Close to 80% of the R mutants least resistant to phagocytosis accumulated in the dextran-rich phase, whereas more phagocytosis-resistant mutants showed higher affinity for the interface and the polyethylene glycol-rich top phase. By growing the uridine diphosphate (pyro)-gal-4-epimeraseless mutant LT2-M1 in the presence of d-galactose for different periods of time, two well-defined peaks were obtained in counter-current distribution analysis with an aqueous two-polymer phase system revealing a heterogeneous population in the culture. One peak was located at a site characteristic of R bacteria, the other at the site of S bacteria. As growth proceeded, more bacteria transferred from the R-type to the S-type peak. Within each peak, a gradual increase in resistance to phagocytosis by rabbit polymorphonuclear cells occurred with increasing length of growth in d-galactose.