Identity of macromolecules present in the extracellular slime layer of Staphylococcus epidermidis

A physico-chemical study of the interaction of ethanolic extracts of propolis with bacterial cells

In the present study, an effort has been made to understand the interaction mode of propolis, a natural substance produced by honey bees, with gram-positive and gram-negative bacterial cells by measuring alterations in cell surface physico-chemical properties following the incubation of the cells with different sub-inhibitory concentrations of this antimicrobial agent. Electrophoretic mobility and surface hydrophobicity measurements revealed for the first time that propolis induced substantial changes in the volumetric charge density, electrophoretic softness and degree of hydrophobicity characterizing the outermost surface layer of cells. These changes, which appear to be dose-dependent, seem to be consistent with the increasing accumulation and penetration of the propolis antimicrobial components through the cells extracellular layer. Moreover, electron microscopy observation and the determination of the cell constituents' release demonstrated that propolis at sub-bactericidal concentrations already provoked (at least localized) cell wall damage and/or perturbations. These findings thus suggest that the initial mechanism of action of propolis is most likely structural, resulting from sufficient interaction between the different propolis components and bacterial cell wall structures.

Identification of individual biofilm-forming bacterial cells using Raman tweezers

A method for in vitro identification of individual bacterial cells is presented. The method is based on a combination of optical tweezers for spatial trapping of individual bacterial cells and Raman microspectroscopy for acquisition of spectral “Raman fingerprints” obtained from the trapped cell. Here, Raman spectra were taken from the biofilm-forming cells without the influence of an extracellular matrix and were compared with biofilm-negative cells. Results of principal component analyses of Raman spectra enabled us to distinguish between the two strains of Staphylococcus epidermidis. Thus, we propose that Raman tweezers can become the technique of choice for a clearer understanding of the processes involved in bacterial biofilms which constitute a highly privileged way of life for bacteria, protected from the external environment.

Influence of papain in biofilm formed by methicillin-resistant Staphylococcus epidermidis and methicillin-resistant Staphylococcus haemolyticus isolates

Methicillin-resistant Staphylococcus epidermidis (MRSE) and methicillin-resistant Staphylococcus haemolyticus (MRSHa) are important coagulase-negative staphylococci. They are often isolated from bacteremia in humans mainly due to their ability to form biofilm on the surfaces of medical devices. Papain is a complex mixture of proteolytic enzymes and peroxidases extracted from the latex of Carica papaya and it is recognized by accelerating the healing process of wounds. This study aimed to evaluate the ability of the MRSE and MRSHa isolates to produce biofilms. Besides this, the ability of papain to inhibit the formation of biofilms or to disrupt the ones already formed by those bacteria was analyzed. Thirty MRSHa and 30 MRSE were isolated from bacteremia and used in this study. It was observed that papain has ability to reduce biofilms formed by MRSE (p < 0.06) and by MRSHa (p = 0.0005). In addition, papain was able to disrupt mature biofilms made by MRSE (p = 0.014). No antibacterial activity of papain was observed for any isolates of MRSE and MRSHa tested. Papain has been demonstrated as a potential product for reducing biofilm.

Molar mass, entanglement, and associations of the biofilm polysaccharide of Staphylococcus epidermidis

Biofilms are microbial communities that are characterized by the presence of a viscoelastic extracellular polymeric substance (EPS). Studies have shown that polysaccharides, along with proteins and DNA, are a major constituent of the EPS and play a dominant role in mediating its microstructure and rheological properties. Here, we investigate the possibility of entanglements and associative complexes in solutions of extracellular polysaccharide intercellular adhesin (PIA) extracted from Staphylococcus epidermidis biofilms. We report that the weight average molar mass and radius of gyration of PIA isolates are 2.01×10(5)±1200 g/mol and 29.2±1.2 nm, respectively. The coil overlap concentration, c*, was thus determined to be (32±4)×10(-4) g/mL. Measurements of the in situ concentration of PIA (cPIA,biofilm) was found to be (10±2)×10(-4) g/mL.Thus, cPIA,biofilm Collapse

Key Words

• staphylococcus epidermidis
• biofilm
• entangled polymers
• polysaccharide-protein complex
• extracellular polysaccharides
• static light scattering

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MESH Headings

• Animals
• Bacterial Adhesion
• Biofilms/growth & development
• Carbohydrate Conformation
• Cattle
• Elasticity
• Hydrogen Bonding
• Hydrogen-Ion Concentration
• Polysaccharides, Bacterial/chemistry
• Polysaccharides, Bacterial/isolation & purification
• Protein Binding
• Serum Albumin, Bovine/chemistry
• Staphylococcus epidermidis/chemistry
• Static Electricity
• Viscosity

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Grants

• R01 GM069438 NIGMS NIH HHS
• R01 GM081702 NIGMS NIH HHS
• GM-069438 NIGMS NIH HHS

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Affiliation(s)

Mahesh Ganesan Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48105
Elizabeth J. Stewart Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48105
Jacob Szafranski Department of Emergency Medicine, University of Michigan, Ann Arbor, MI 48105
Ashley Satorius Department of Emergency Medicine, University of Michigan, Ann Arbor, MI 48105
John G. Younger Department of Emergency Medicine, University of Michigan, Ann Arbor, MI 48105
Michael J. Solomon Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48105

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An extracellular Staphylococcus epidermidis polysaccharide: relation to Polysaccharide Intercellular Adhesin and its implication in phagocytosis

BACKGROUND

The skin commensal and opportunistic pathogen Staphylococcus epidermidis is a leading cause of hospital-acquired and biomaterial-associated infections. The polysaccharide intercellular adhesin (PIA), a homoglycan composed of β-1,6-linked N-acetylglucosamine residues, synthesized by enzymes encoded in icaADBC is a major functional factor in biofilm accumulation, promoting virulence in experimental biomaterial-associated S. epidermidis infection. Extracellular mucous layer extracts of S. epidermidis contain another major polysaccharide, referred to as 20-kDa polysaccharide (20-kDaPS), composed mainly out of glucose, N-acetylglucosamine, and being partially sulfated. 20-kDaPS antiserum prevents adhesion of S. epidermidis on endothelial cells and development of experimental keratitis in rabbits. Here we provide experimental evidence that 20-kDaPS and PIA represent distinct molecules and that 20-kDaPS is implicated in endocytosis of S. epidermidis bacterial cells by human monocyte-derived macrophages.

RESULTS

Analysis of 75 clinical coagulase-negative staphylococci from blood-cultures and central venous catheter tips indicated that 20-kDaPS is expressed exclusively in S. epidermidis but not in other coagulase-negative staphylococcal species. Tn917-insertion in various locations in icaADBC in mutants M10, M22, M23, and M24 of S. epidermidis 1457 are abolished for PIA synthesis, while 20-kDaPS expression appears unaltered as compared to wild-type strains using specific anti-PIA and anti-20-kDaPS antisera. While periodate oxidation and dispersin B treatments abolish immuno-reactivity and intercellular adhesive properties of PIA, no abrogative activity is exerted towards 20-kDaPS immunochemical reactivity following these treatments. PIA polysaccharide I-containing fractions eluting from Q-Sepharose were devoid of detectable 20-kDaPS using specific ELISA. Preincubation of non-20-kDaPS-producing clinical strain with increasing amounts of 20-kDaPS inhibits endocytosis by human macrophages, whereas, preincubation of 20-kDaPS-producing strain ATCC35983 with 20-kDaPS antiserum enhances bacterial endocytosis by human macrophages.

CONCLUSIONS

In conclusion, icaADBC is not involved in 20-kDaPS synthesis, while the chemical and chromatographic properties of PIA and 20-kDaPS are distinct. 20-kDaPS exhibits anti-phagocytic properties, whereas, 20-kDaPS antiserum may have a beneficial effect on combating infection by 20-kDaPS-producing S. epidermidis.

Adherence of Staphylococcus epidermidis to human endothelial cells is associated with a polysaccharidic component of its extracellular mucous layer

Bacterial adherence to eukaryotic cells is highly contributing to microbial pathogenesis. Bacterial adhesins, macromolecules, and glycosaminoglycan chains of the endothelial cell surface have been implicated in staphylococcal attachment. Our research group has isolated an antigenic polysaccharidic component of Staphylococcus epidermidis extracellular layer, known as 20-kDa PS (PS), and showed that antibodies against this polysaccharide protect from infections. Therefore, the role of PS in S. epidermidis adherence to endothelial cells was studied. For this purpose we examined the impact of PS on the ability of two S. epidermidis strains (a PS-producing and a non-PS-producing strain) to adhere to human endothelial cells in the presence or absence of specific antibodies to this polysaccharide. Hence, it is established that exogenous chondroitin sulfate (CS) decreases, in part, the S. epidermidis' attachment to endothelial cells and the antagonistic binding effect of CS and PS was also studied. The results obtained demonstrate that PS facilitates the adherence of S. epidermidis to both strains. CS abolished the PS-induced adherence in PS-producing strain and partially in the non-PS-producing one. Conclusively, the adherence of S. epidermidis to human endothelial cells is associated with its extracellular PS component and it is suggested that the bacterial binding via glycosaminoglycan chains is an important mechanism underlining the PS-induced binding to endothelial cells.

A modified protocol for isolation and purity evaluation of a staphylococcal acidic polysaccharide by chromatography and capillary electrophoresis

The extracellular slime of Staphylococcus epidermidis contains, amongst various macromolecules, an acidic polysaccharide (PS) of a molecular mass of 20 kDa with significant antigenic and biological properties. The isolation procedure used so far includes multiple fractionations in anion-exchange chromatographic columns before its final purification by gel filtration chromatography. This protocol is laborious, time-consuming and includes the risk of unnecessary loss of PS quantities. Because of the significance of this PS, a modified protocol resulting in an easier and quicker isolation procedure was developed. Furthermore, identification, purity, charge density and molecular integrity of the isolated polysaccharide were evaluated by a reverse-polarity capillary electrophoresis method.

Immunization with Specific Polysaccharide Antigen Reduces Alterations in Corneal Proteoglycans During Experimental Slime-ProducingStaphylococcus epidermidisKeratitis

PURPOSE

Staphylococcus epidermidis is a leading cause of bacterial keratitis associated with corneal damage. Corneal integrity is closely associated with matrix macromolecules, such as proteoglycans (PGs) and collagen. The aim of this study was to examine whether active immunization (AI) using a major immunogenic polysaccharide determinant of slime (20-kDa PS) as antigen, and passive immunization (PI) after administration of specific antibodies toward 20-kDa PS affect the distribution of PGs as well as corneal lesions in an experimental model of slime-producing S. epidermidis keratitis.

METHODS

For AI, seven rabbits were immunized with 20-kDa PS, whereas for PI, seven rabbits received specific antibodies against 20-kDa PS. Lesions were graded clinically for a 21-day period. Levels of 20-kDa PS antibodies in serum and aqueous humor in both immunization groups were determined by ELISA. The distribution of certain extracellular matrix PGs during corneal healing was analyzed immunohistochemically.

RESULTS

Levels of specific anti-20-kDa PS antibodies in serum and aqueous humor obtained after either AI or PI were significantly higher as compared with those in the respective nonimmunized control groups (p<0.001). Clinical grading showed that both AI and PI rabbits had a significantly less corneal damage as compared with infected nontreated rabbits. Immunohistochemical analyses for PGs exhibited significant differences to the wounded regions as compared with noninfected corneal tissue. Accumulation of keratan sulfate PGs and decorin was observed in the corneal stroma of infected rabbits and of heparan sulfate PGs around the new-formed vessels. This phenomenon was significantly reduced in immunized animals in accordance with macroscopically decreased corneal damage observed in these animals.

CONCLUSIONS

Results of this study suggest a key role of 20-kDa PS and its antibodies as prophylactic and therapeutic agents in keratitis caused by slime-producing S. epidermidis.

Neuraminidase produces a decrease of adherence of slime-forming Staphylococcus aureus to gelatin-impregnated polyester fiber graft fabric: an experimental study

Because slime-forming microorganisms are the major causative agents of graft infections, we aimed to investigate bacterial adherence in slime-forming and nonslime-forming Staphylococcus aureus and to determine the role of neuraminidase (NANase) on adherence to gelatin-impregnated polyester fiber graft fabric. An in vitro model was developed to quantitatively measure bacterial adherence to the surface of the graft. The grafts were divided into two groups - those colonized with slime-forming S. aureus and those colonized with nonslime-forming S. aureus. The grafts were put into sterile tubes and human plasma was instilled and incubated at 37 degrees C to perform fibrin deposition on the grafts. After 48 h of incubation, grafts were drained and inoculated with slime-forming or nonslime-forming S. aureus in triptic soy broth in the presence or absence of NANase. Following 36 h of incubation at 36 degrees C, grafts were vortexed and cultured to perform a colony count. Bacterial counts were expressed as total colony-forming units per square centimeter of graft. Slime-forming S. aureus had greater affinity with the graft compared with nonslime-forming S. aureus (P < 0.05). The adherence of slime-forming S. aureus was impaired by NANase treatment (P < 0.001) but NANase treatment of nonslime-forming S. aureus did not change the adherence to the graft (P > 0.05). These results show that slime plays an important role in the pathogenesis of vascular graft infection. Adherence of slime-forming S. aureus can be decreased by NANase treatment. This may have implications for the development of neuraminidase-embedded vascular grafts to diminish biomaterial-related infections.

Neuraminidase decreases in vitro adherence of slime-forming coagulase-negative staphylococci to biosynthetic ovine collagen vascular graft

Vascular prosthetic graft infection is a major complication of vascular surgery that starts with adhesion of the microorganism to the graft. Because slime-forming microorganisms are the major causative agents in graft infection, the goals of investigators in this study were (1) to investigate the bacterial adherence of slime-forming and non-slime-forming coagulase-negative staphylococci (CNS), and (2) to determine the role of neuraminidase (NANase) in bacterial adherence to the biosynthetic ovine collagen graft. Human plasma was instilled and incubated at 37 degrees C in preparation for fibrin deposition of grafts. After 48 hours, incubation grafts were drained and inoculated with slime-forming and non-slime-forming CNS in tryptic soy broth in the presence and in the absence of neuraminidase. After 24 hours of incubation at 36 degrees C, grafts were vortexed and cultured for colony count. Bacterial counts were expressed as total colony-forming units per longitudinal centimeter of the graft. Slime-forming CNS had greater affinity to the collagen graft compared with non-slime-forming CNS (P<.05). Adherence of slime-forming CNS was impaired by NANase treatment (P<.001). NANase treatment of patients with non-slime-forming CNS did not change adherence to the graft (P>.05). Results show that slime plays an important role in the pathogenesis of vascular graft infection. Adherence of slime-forming CNS can be decreased through the administration of NANase. This may have implications for the development of neuraminidase-embedded vascular grafts designed to reduce the occurrence of biomaterial-related infection.

Enzymatic detachment of Staphylococcus epidermidis biofilms

The gram-positive bacterium Staphylococcus epidermidis is the most common cause of infections associated with catheters and other indwelling medical devices. S. epidermidis produces an extracellular slime that enables it to form adherent biofilms on plastic surfaces. We found that a biofilm-releasing enzyme produced by the gram-negative periodontal pathogen Actinobacillus actinomycetemcomitans rapidly and efficiently removed S. epidermidis biofilms from plastic surfaces. The enzyme worked by releasing extracellular slime from S. epidermidis cells. Precoating surfaces with the enzyme prevented S. epidermidis biofilm formation. Our findings demonstrate that biofilm-releasing enzymes can exhibit broad-spectrum activity and that these enzymes may be useful as antibiofilm agents.

Neuraminidase produces dose-dependent decrease of slime production and adherence of slime-forming, coagulase-negative staphylococci

BACKGROUND

Slime is one of the important structures of certain bacterial strains involved in nonspecific adherence. This study was conducted to determine the role of neuraminidase on slime formation and adherence of slime-forming coagulase-negative staphylococci to inert surface.

METHODS

Quantitative biofilm and qualitative bacterial adherence assays were performed with increasing concentrations of neuraminidase extracted from Clostridium perfringens-treated bacteria in polystyrene plates and polypropylene tubes.

RESULTS

Slime production of slime-forming, coagulase-negative staphylococci was significantly decreased dose dependently at > or =100 mU/mL (p <0.001). Bacterial adherence to smooth surface was impeded at > or =100 mU/mL of neuraminidase treatment and adherence results were comparable with slime production assay results.

CONCLUSIONS

Sialic acid may be a constituent molecule of slime and involved in bacterial adherence to inert surface. These results represent new insight into the mechanism of slime production and adherence of slime-forming, coagulase-negative staphylococci to inert surface.

Potential use of solid phase immunoassays in the diagnosis of coagulase-negative staphylococcal infections

Staphylococcus epidermidis is a major nosocomial pathogen, even though it is a member of the normal bacterial flora of skin and the mucous membranes. A major complication is the development of biofilms on implanted medical devices. Diagnosis of coagulase-negative staphylococcal infections relies on the presence of clinical manifestation of infections and on microbiologic evidence, usually obtained after the removal of the biomaterial. Solid-phase immunoassays have not yet been used for routine diagnosis of coagulase-negative staphylococcal infections and distinction between pathogenic and normal cocci. The enzyme immunoassays developed in the last decade are presented in this review article. Serodiagnosis has been attempted by determining antibodies against bacterial cells, mixtures of S. epidermidis slime antigens and discrete slime antigens. Detection or typing of staphylococcal cells has been performed by specific antibodies and lectins. There is still a long way until the application of such assays in the routine clinical laboratory and large clinical studies are necessary.

Levels of specific antibodies towards the major antigenic determinant of slime-producing Staphylococcus epidermidis determined by an enzyme immunoassay and their protective effect in experimental keratitis

Staphylococcus epidermidis is an important cause of bacterial keratitis. Certain S. epidermidis strains produce an extracellular slime layer rich in an acidic polysaccharide with a molecular size of 20 kDa (20-kDa PS). We have demonstrated that the level of 20-kDa PS-specific antibodies significantly rises after establishment of slime-producing S. epidermidis bacteraemia and, furthermore, that rabbit polyclonal antibodies to 20-kDa PS opsonize cells of slime-producing S. epidermidis to a great degree and promote their clearance by polymorphonuclear cells (Arch. Biochem. Biophys. 342 (1997) 389; J. Pharm. Biomed. Anal. 22 (2000) 1029). The purpose of this study was to examine the protective and therapeutic effects both of active immunization, using 20-kDa PS as antigen, and of passive administration of specific antibodies towards the 20-kDa PS in a rabbit keratitis model. For active immunization, 20 rabbits were subcutaneously immunized with 20-kDa PS, whereas for passive immunization specific polyclonal IgG antibodies against 20-kDa PS were administered to 20 rabbits 1 day before induction of infection. Clinical observations were made weekly for 1 month and levels of 20-kDa PS antibodies in serum and aqueous humor in both immunization groups were determined by an enzyme immunoassay. The levels of specific anti-20-kDa PS IgG in serum and aqueous humor following either active or passive immunization were significantly higher as compared with control groups (P<0.001). Although, actively immunized rabbits showed significantly less corneal damage than control animals, passively immunized ones were significantly better protected as compared with both control and those actively immunized. Obtained results suggest that 20-kDa PS plays crucial role in the pathogenesis of S. epidermidis keratitis and that both types of immunization significantly protect against corneal S. epidermidis pathology and damage.

Immunoreactivity of 80-kDa peptidoglycan and teichoic acid-like substance of slime producing S. epidermidis and specificity of their antibodies studied by an enzyme immunoassay

S. epidermidis is considered an important cause of nosocomial bacteraernia in immunocompromized hosts as well as the commonest agent of sepsis in patients with prosthetic devices. Pathogenesis is attributed to adherence and growth on bioniaterials facilitated by production of extracellular slime. The major macromolecules of slime are: a 20-kDa acidic polysaccharide (20-kDa PS) comprising the 60% of carbohydrate-containing slime macromolecules, a peptidoglycan with average molecular size of 80-kDa (30% of slime dry weight) and cell wall teichoic acid-like substance. In this study, antibodies to these macromolecules as well as crude slime were raised in rabbits and their immunological reactivity and specificity were studied by an enzyme immunoassay. All isolated macromolecules induced the production of specific antibodies. 20-kDa PS was less immunogenic than 80-kDa peptidoglycan and teichoic acid-like substance. However, 20-kDa PS was the most potent inhibitor of the reaction of slime with its homologous antibodies revealing that this polysaccharide is the major antigenic determinant of slime. All three antibodies specifically recognize (p < 0.05) and react with slime-producing S. epidermidis in comparison to other staphylococci species. Obtained results indicate that the 20-kDa PS may be distributed in the surface of the slime exposing most of its antigenic determinants to the immune system, whereas those of 80-kDa peptidoglycan and teichoic acid-like substance seem to be less accessible.

Immunochemical-based assays in the bioanalysis of immunoglobulins

Intravenous immunoglobulin (IVIG) preparations consist of IgG derived from a pool of human plasma of healthy individuals and have been used as routine treatment of patients with primary and secondary immunodeficiencies, autoimmune, and/or inflammatory diseases. Emergence of new infectious agents and development of antibiotic resistance in many bacteria have posed serious problems in the treatment of infections. Since IVIGs contain natural antibodies that occur in the healthy population, their administration to immunocompromised hosts either as a prophylactic agent or as complementary treatment to the usual antimicrobial treatment have been studied. Contradictory results obtained by several clinical studies in respect to the clinical efficacy of IVIGs have in part been ascribed to the poor characterization of IVIG preparations in terms of their specific antibody content against the various pathogenic microorganisms. Immunoassays constitute a promising tool for bioanalysis of IVIGs thanks to the high sensitivity, repeatability and ease of implementation. Ensuring high selectivity, enzyme immunoassays have been used for determination of the levels of pathogen-specific antibodies in IVIG preparations. In this review, the application of immunoassays monitoring such specific antibodies in IVIGs and the relationship of estimated titers with their in vitro opsonic activity are summarized. The relationship of the content of specific antibodies in IVIGs and their functional efficacy with the outcome of clinical studies including patients with primary immunodeficiencies and premature neonates treated with IVIGs is also discussed.

Determination of slime-producing S. epidermidis specific antibodies in human immunoglobulin preparations and blood sera by an enzyme immunoassay: correlation of antibody titers with opsonic activity and application to preterm neonates

Slime-producing Staphylococcus epidermidis is responsible for severe infections in immunocompromised patients and, particularly, in premature infants who are transiently deficient in IgG. A sulfated polysaccharide with molecular mass of 20-kDa (20-kDa PS) has been recognized as the major polysaccharide component and antigenic determinant of S. epidermidis extracellular slime layer. The presence of adequate amounts of antibodies to 20-kDa PS in patients' sera would be of importance to prevent or treat slime-producing S. epidermidis bacteremia. Administration of intravenous immunoglobulin (IVIG) is considered to be a reasonable IgG replacement therapy and has been widely used to prevent or treat neonatal sepsis. Clinical trials have shown conflicting results on the efficacy of IVIGs and this phenomenon has been attributed to the variability of IVIG preparations in the content and opsonic activity of IgG against microorganisms of clinical importance. Monitoring of antibodies to distinct bacterial macromolecules, which are species-specific and responsible for bacterial infections, has not been performed previously. A highly precise and repeatable enzyme immunoassay was developed to determine quantitatively the levels of antibodies against the 20-kDa PS of S. epidermidis slime. The amount of 20-kDa PS specific antibodies found in 27 lots of an IVIG preparation (Sandoglobulin) correlated well with their in vitro opsonic activity against slime-producing S. epidermidis. The majority of lots (75%) having titers higher than 200 units/ml showed significant opsonic activity (50-75%) towards slime-producing S. epidermidis. Sandoglobulin lots with titers higher than 200 units/ml of 20-kDa PS specific IgG were administered as a prophylactic agent to low-birth weight (lower than 1700 g) preterm neonates immediately after birth. The levels of total and 20-kDa PS specific IgG in neonates' blood sera were significantly higher than those found in the control group, even 10 days after the last infusion. The rate of slime-producing S. epidermidis bacteremia in neonates who received IVIG was also considerably lower than those in the control group. The results of this study suggest that specific IgG titers estimated by the developed enzyme immunoassay may well be indicative of the IVIG opsonic activity against slime-producing S. epidermidis. Furthermore, administration of Sandoglobulin with titers higher than a cut-off value of 200 units/ml may significantly protect preterm neonates against slime-producing S. epidermidis bacteremia.

Molecular mechanisms of Staphylococcus epidermidis biofilm formation

Coagulase-negative staphylococci, mainly Staphylococcus epidermidis, are the predominant cause of implanted medical-device related infections. The formation of adherent multi-layered biofilms embedded into a glycocalyx composed of exopolysaccharides on implanted devices is believed to be essential for the pathogenesis of S. epidermidis infections. Biofilm formation may be separated into primary attachment of bacteria to native or modified polymer surfaces followed by proliferation of attached bacterial cells leading to accumulation of multi-layered cell-clusters and glycocalyx formation. Recent progress in the understanding of the molecular mechanisms cooperating in S. epidermidis biofilm formation is reviewed and current thinking on the relevance of these mechanisms for S. epidermidis device-related infections is discussed.

The major 20-kDa polysaccharide of Staphylococcus epidermidis extracellular slime and its antibodies as powerful agents for detecting antibodies in blood serum and differentiating among slime-positive and -negative S. epidermidis and other staphylococci species

Staphylococcus epidermidis has been recognized as an important pathogen in immunocompromised hosts and patients with prosthetic or implanted medical devices. A highly adhesive extracellular material (slime or biofilm) produced by certain strains is associated with bacterial adherence to and growth on biomaterials contributing to pathogenesis of bacteremia. We have recently reported on the isolation and characterization of a sulfated 20-kDa acidic polysaccharide which constitutes slime's major component. Immunization of rabbits with crude slime and 20-kDa polysaccharide gave rise to readily reactive sera without manipulation of the 20-kDa polysaccharide structure. Immunological studies using purified polyclonal antibodies to 20-kDa polysaccharide by direct and competitive ELISA showed that they exhibit a high degree of reactivity and specificity with the homologous antigen. A significant proportion of the reactivity of antibodies to crude slime was also shown to be attributed to the 20-kDa polysaccharide. This polysaccharide is immunogenic in humans since blood sera derived from patients 10-15 days after confirmation of slime-producing S. epidermidis bacteremia gave approximately 16 times higher reactivity than that of healthy individuals. Antibodies to 20-kDa polysaccharide were able to recognize and react specifically with slime-positive S. epidermidis strains compared to slime-negative ones (2 to 5 times higher reactivity). Moreover, these antibodies exhibited statistically significant (P < 0.05) differences in the degree of reactivity among S. epidermidis and other staphylococci species. These results open a new area in the diagnosis of S. epidermidis infection by direct analysis in blood sera, in differentiating among slime-positive and slime-negative strains as well as in distinguishing slime-producing S. epidermidis from other staphylococci species by simple laboratory tests.

Proteoglycan synthesis induced by transforming and basic fibroblast growth factors in human malignant mesothelioma is mediated through specific receptors and the tyrosine kinase intracellular pathway

The effects and the mechanisms of action of transforming (TGF-beta 2) and basic fibroblast (bFGF) growth factors on the synthesis of hyaluronan and proteoglycans (PGs) in human malignant mesothelioma cells have been studied. Two cell lines, one with an epithelial differentiation (STAV-AB) and the other with a fibroblast-like phenotype (STAV-FCS) have been examined. Using monoclonal antibodies to growth factor receptors, the presence of a high density of the specific receptors for TGF-beta 2 and bFGF was immunochemically demonstrated in both mesothelioma cell lines. These cell lines synthesize hyaluronan, galactosaminoglycan containing PGs (GalAGPGs) and heparan sulphate containing PGs (HSPGs) at different levels; the epithelial differentiated cells produce a 6-8 times higher amount than those with the fibroblast-like morphology. In both cell lines the rates of proteoglycan synthesis were affected in a dose-dependent mode by TGF-beta 2 and bFGF. Maximal synthetic levels of both secreted and cell-bound proteoglycans were reached at 10 ng/mL whereafter they remained constant. TGF-beta 2 stimulated the synthesis of hyaluronan, GalAGPGs and of HSPGs in STAV-FCS, whereas this effect was pronounced only for GalAGPGs in STAV-AB. bFGF showed stimulatory effects for the synthesis of hyaluronan and cell associated GalAGPGs in STAV-FCS, whereas no significant enhancement was recorded for HSPGs. In the STAV-AB cell line the synthesis of hyaluronan and GalAGPGs remained unaltered by the addition of both growth factors. Although the synthesis of total HSPGs remained constant, this was due to a decrease in the secreted product and a similar increase of the cell-associated proteoglycan. The stimulatory mechanisms of both growth factors was examined by using the specific protein tyrosine kinase inhibitor genistein. Incubation of both cell lines with this isoflavonoid inhibited the enhanced synthesis of hyaluronan and all PGs induced by TGF-beta 2 and bFGF. It is suggested that most, if not all, of the stimulatory effects on the hyaluronan and PGs synthesis are mediated via protein tyrosine kinase activity elicited by receptor-ligand complexes. Decreased synthetic rates obtained when giving genistein to unstimulated mesothelioma cells may indicate the relation of hyaluronan and PGs synthesis with an autocrine stimulatory mechanisms.

Isolation, biochemical and immunological characterisation of two sea urchin glycoproteins bearing sulphated poly(sialic acid) polysaccharides rich in N-glycolyl neuraminic acid

Two different sialoproteins were isolated from the sea urchin shell by guanidine hydrochloride extraction in the presence of Triton X-100. The sialoproteins (SP I and SP II) were purified on DEAE-Sephacel and Sepharose CL-6B and separated from each other by density gradient centrifugation. The ratio between recovered SP I and SP II was 1:4.5 and their M(r)s 650 and 600 kDa, respectively. They were degraded by neuraminidase, endoglycosidase F and peptide N-glycosidase F resulting in fragments of similar relative molecular mass (M(r)s). Although their protein cores have approximately the same relative molecular mass of 500 kDa, they differ markedly in their contents of aspartic acid/asparagine, glycine, leucine and phenylalanine, as well as in the primary amino acid sequence of their N-terminal peptides. Carbohydrate analyses showed that the sialic acid content was higher in SP I (11.4% of dry tissue weight) than in the more prominent SP II (5.3%). Two types of carbohydrates, O-glycosidically-linked polysaccharides and N-glycosidically-linked oligosaccharides are present in both sialoproteins. SP I contains 10-11 polysaccharide chains whereas SP II contains 5-6. The polysaccharides are linked to protein cores via galactosamine, have approximately the same M(r) of 12 kDa and contain 32-33 N-glycolyl neuraminic acid, 10-11 glucosamine, 6-7 sulphate and 6-8 neutral monosaccharide residues. Sialic acid residues are organized in a poly(sialic acid) unit which is present in the non-reducing terminal of the polysaccharides and degraded by neuraminidase. Hexosamines, sulphates and neutral monosaccharides are all constituents of the sialic acid free region of the chain near the reducing end. Two oligosaccharide populations were isolated from SP I, one major (70% of the total oligosaccharides) with M(r) of approximately 3 kDa and the other with M(r) of 1.5 kDa. In SP II, however, only a 3-kDa oligosaccharide population was present. The oligosaccharides from both sialoproteins are N-glycosidically linked to asparagine via the glucosamine and contain mannose, glucosamine, galactosamine and sialic acids. Antibodies against SP II were raised in rabbits and it was shown that the antigenicity of SP II was lost on either neuraminidase or trypsin digestion, indicating that both the poly(sialic acid) units of the polysaccharide and the protein core are antigenically active. As expected, SP II showed considerable cross-reactivity with SP I due to the common poly(sialic acid) structure. There were no significant reactivities of SP II and SP I with antibodies to bovine bone sialoprotein and osteopontin. The biological role of the two sea urchin sialoproteins as developmentally regulated products of the tissue remains to be elucidated.