DENSITY-GRADIENT PATTERNS OF STAPHYLOCOCCUS AUREUS CELLS AND CELL WALLS DURING GROWTH AND MECHANICAL DISRUPTION

Mechanical damage to Escherichia coli cells in a model of amino-acid crystal fermentation

We investigated the mechanical damage to the Escherichia coli cell caused by polyvinyl chloride particles as a model of amino-acid crystal fermentation. Our results indicated that the glucose-consumption rate and the intracellular ATP concentration temporarily increased by the mechanical damage, and decreased after considerable damage had occurred on cell membrane.

Methicillin resistant Staphylococcus aureus adhesion to human umbilical vein endothelial cells demonstrates wall shear stress dependent behaviour

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is an increasingly prevalent pathogen capable of causing severe vascular infections. The goal of this work was to investigate the role of shear stress in early adhesion events.

Methods

Human umbilical vein endothelial cells (HUVEC) were exposed to MRSA for 15-60 minutes and shear stresses of 0-1.2 Pa in a parallel plate flow chamber system. Confocal microscopy stacks were captured and analyzed to assess the number of MRSA. Flow chamber parameters were validated using micro-particle image velocimetry (PIV) and computational fluid dynamics modelling (CFD).

Results

Under static conditions, MRSA adhered to, and were internalized by, more than 80% of HUVEC at 15 minutes, and almost 100% of the cells at 1 hour. At 30 minutes, there was no change in the percent HUVEC infected between static and low flow (0.24 Pa), but a 15% decrease was seen at 1.2 Pa. The average number of MRSA per HUVEC decreased 22% between static and 0.24 Pa, and 37% between 0.24 Pa and 1.2 Pa. However, when corrected for changes in bacterial concentration near the surface due to flow, bacteria per area was shown to increase at 0.24 Pa compared to static, with a subsequent decline at 1.2 Pa.

Conclusions

This study demonstrates that MRSA adhesion to endothelial cells is strongly influenced by flow conditions and time, and that MSRA adhere in greater numbers to regions of low shear stress. These areas are common in arterial bifurcations, locations also susceptible to generation of atherosclerosis.

Teichoic acid enhances adhesion of Staphylococcus epidermidis to immobilized fibronectin

Adhesion is a prerequisite for coagulase-negative staphylococci to cause invasive disease and may be mediated by adhesive host molecules adsorbed on implanted polymers. In this study, we can confirm previous observations demonstrating binding of Staphylococcus epidermidis to fibronectin (FN) adsorbed polymer surfaces. So far, the nature of FN-recognizing adhesin(s) in S. epidermidis remains elusive. Since teichoic acids (TA) have been shown to exert binding functions for extracellular matrix molecules in several Gram-positive species, we have purified wall TA of S. epidermidis laboratory strains KH11 and RP62A, as well as clinical isolate AB9. Using a polymethylmethacrylate (PMMA) coverslip adhesion assay, a microtitre plate assay and a particle agglutination assay, we found that purified TA significantly enhanced adhesion of S. epidermidis KH11 and RP62A to FN coated surfaces. Enhanced adhesion was dose-dependent and saturable. Preincubation, either of microorganisms or of FN coated surfaces, with TA promoted adhesion, while adhesion to TA-adsorbed PMMA was comparably low. This observation may suggest a potential role of cell wall carbohydrates as bridging molecules between microorganisms and immobilized FN in early steps of S. epidermidis pathogenesis.

Streptolysin S activation by lipoteichoic acid

Lipoteichoic acid from streptococci and Staphylococcus aureus both activated membrane-bound precursor streptolysin S and induced the formation of extracellular streptolysin S. Lipoteichoic acid could replace other substances, such as yeast ribonucleic acid core, that act as carriers for hemolysin but which are not components of the streptococcus or the host. Lipoteichoic acid may play a role as the physiological carrier of streptolysin S to host tissues.

Cell wall composition of novobiocin-resistant pleiotropic mutant staphylococci

Physically purified cell walls were prepared from selected pleiotropic novobiocin-resistant staphylococcal strains. The quantitative amino acid, amino sugar, and phosphorus contents of these walls are reported. This pleiotype was culturally diagnosed by its inability to support the growth of typing phages, inability to release latent bacteriophage, failure to elaborate coagulase, altered sugar catabolic pattern, and resistance to novobiocin. The strains were divided into two groups on the basis of wall composition. The walls of both groups of strains appeared to possess at least two phosphorus-containing polymers. On group of strains contained elevated levels of phosphorus in the cell walls. The second group contained the novel amino sugar galactosamine in the cell walls. This amino sugar is probably associated with one of the phosphorus-containing wall polymers of this group. On the basis of the data presented, it is suggested that the pleiotropy of these strains is the result of genetic change in the control of the biosynthesis of teichoic acids.

Lipoteichoic acid localization in mesosomal vesicles of Staphylococcus aureus

Mesosomal vesicles and plasma membranes of Staphylococcus aureus ATCC 6538P have been prepared and examined for the presence of lipoteichoic acid. Lipids were first removed by treatment with pyridine-acetic acid-butanol (22:31:100, vol/vol/vol) and chloroform-methanol (2:1, vol/vol). Subsequently, lipoteichoic acid was removed with 40% phenol in water. The lipoteichoic acid from mesosomal vesicles was characterized by (i) equimolar glycerol and phosphate, (ii) alanine upon hydrolysis (2 N NH(4)OH, 18 h, 22 C), and (iii) fatty acids, diglycerol triphosphate, glycerol monophosphate, and glycerol diphosphate upon alkaline hydrolysis (1 N NaOH, 3h, 100 C). The plasma membranes contained no lipoteichoic acid. The presence in mesosomal vesicles of 18% of the dry weight as lipoteichoic acid and its absence from plasma membranes provide the first major chemical differences between these organelles. A study of the lipoteichoic acid content in various fractions of the cell showed that the mesosomal vesicles were the major and probably the sole site for the localization of the lipoteichoic acid in these organisms. A new method for the preparation of mesosomes in increased yields is reported. A theory for the control of cell division involving lipoteichoic acid and the mesosome is proposed.

Simple, inexpensive procedure for the disruption of bacteria

Small volumes (1 to 2 ml) of bacterial cultures, with turbidities ranging from 3 to 10, were disrupted 50 to 90% (measured as a decrease in turbidity) within 2 min, by shaking them on a Vortex-type mixer in the presence of glass beads. This method of disrupton was effective for cells in the following genera: Streptococcus, Lactobacillus, Staphylococcus, Bacillus, and Escherichia. After low-speed centrifugation, the resulting extract can be used as potential sources for enzymes, transforming deoxyribonucleic acids, cell walls, membranes, etc.

Serological and cellular immune activity of peptidoglucomannan fractions of Candida albicans cell walls

A two-stage extraction of isolated cell walls of C. albicans resulted in 45% solubilization into antigens of high molecular weight leaving a wall residue which also had antigenic properties. Ice-cold dilute alkali removed 25% of the defatted cell walls. The extract was nondialyzable, had a glucose-to-mannose ratio of 2:3 and an amino acid content of 7.32%, and was designated peptidoglucomannan (PGM). An additional 26% of the walls resistant to stage I were solubilized by sonic treatment yielding a fraction having a glucose-to-mannose ratio of 6:1, termed soluble mannoglucan (sMG). The residue after extraction and sonic treatment contained 10.9% mannose, which was the insoluble mannoglucan. The gel permeation behavior of PGM and sMG on BioGel A5M was similar; each contained two components, one estimated to exceed 5 x 10(6) molecular weight and a second smaller species. The soluble cell wall fractions were active in immunodiffusion and carried antigenic group specificity. Immunoelectrophoresis of PGM, sMG, and mannan revealed some heterogeneity. The insoluble mannoglucan had agglutinating activity. A distinctive immunodiffusion pattern of cell wall antigens was formed with the serum of a leukemic patient with candidiasis. All three cell wall antigens and mannan elicited delayed-type hypersensitivity as measured by skin-test and specific inhibition of macrophage migration. A dose of 25 mug of PGM was sufficient to inhibit 89.9% migration in the peritoneal exudates of guinea pigs immunized with cell walls, and 10 mug of PGM inhibited 91.7% migration in guinea pigs immunized with insoluble mannoglucan.

Specificity of the autolysin of Streptococcus (Diplococcus) pneumoniae

A Streptococcus (Diplococcus) pneumoniae autolysin, partially purified from cellular autolysates, was optimally active at pH 7.0 and was stimulated by monovalent cations. Addition of autolysin to walls resulted in the appearance of only N-terminal l-alanine, whereas no glycosidase activity was observed. Walls which had been solubilized by autolysin were separated by gel filtration into a low-molecular-weight peptide containing amino acids in the same ratios found in intact walls and a high molecular fraction containing the amino acid-deficient peptidoglycan backbone. Thus, the major activity is an N-acetylmuramyl-l-alanine amidase. In addition, walls undergoing spontaneous lysis revealed no glycosidase activity but showed an increase in only N-terminal alanine. Autolysin, which was bound to walls in saline, was almost completely removed when walls were washed in distilled water, and all of the activity was recovered in the water wash fluid.

Degradation of group A streptococcal cell walls by egg-white lysozyme and human lysosomal enzymes

Group A streptococci and their isolated cell walls, normally resistant to egg-white lysozyme and the lysosomal enzymes of human phagocytes, were converted to lysozyme-sensitive forms by partial removal of cell wall carbohydrate, substitution of free amino groups, and by saponification of O-acyl groups. The resultant modified streptococcal cell walls showed rapid degradation when treated with leukocyte granule extract derived from human peripheral blood polymorphonuclear leukocytes and monocytes and when subjected to phagocytosis by living human leukocytes. These results indicate that the factors responsible for lysozyme resistance of the group A cell wall also influence its resistance to human leukocyte granule enzymes and suggest that the chemical composition of the cell wall, in addition to the presence of cell wall carbohydrate, determines this resistance.

Lysis of Staphylococcus aureus cell walls by a soluble staphylococcal enzyme

Enzyme preparations of Staphylococcus aureus were examined for their ability to solubilize (32)P-labeled cell walls of the parent organism. Enzymatic activity was observed in the growth medium, in soluble fractions, and associated with native cell walls. Enzyme associated with isolated cell walls could be inactivated with formaldehyde without reducing the susceptibility of the walls to the action of added enzyme. When cells are frozen and thawed, 50 to 75% of the intracellular enzyme is released along with 2% of the intracellular protein. This freeze-thaw extracted enzyme has little, if any, activity on intact S. aureus cells. It appears that the enzyme resides near the cell wall and acts on the cell-wall inner surface.

Elevated cell wall serine in pleiotropic staphylococcal mutants

Korman, Ruth Z. (Cornell University, Ithaca, N.Y.). Elevated cell wall serine in pleiotropic staphylococcal mutants. J. Bacteriol. 92:762-768. 1966.-Physically purified cell walls were prepared from two staphylococcal strains and from pleiotropic variants derived from them. The quantitative amino acid and amino sugar content of these walls is reported. The pleiotypes, which are identified culturally by their failure to elaborate coagulase, their resistance to bacteriophage, and their sensitivity to mannitol, have altered molar ratios of amino acids and amino sugars in their cell walls. In comparison with lysine content, the serine content of the mutant wall is elevated and the glycine content is reduced. The glucosamine content is reduced also. It is postulated that the pleiotropic mutants possess an altered cell wall biosynthetic pathway.

Freeze-cutting of density gradients

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