Biomedical subjects

L Björck

Publications and source records attributed to L Björck.

At least 19 recordsLinked to original sources

PubMed2003

Interactions between surface proteins of Streptococcus pyogenes and coagulation factors modulate clotting of human plasma.

Invasive and toxic infections caused by Streptococcus pyogenes are connected with high morbidity and mortality. Typical symptoms of these infections are hypotension, edema formation, tissue necrosis, and bleeding disorders. Here we report that components of the coagulation system including fibrinogen, factors V, XI, and XII, and H-kininogen, are assembled at the surface of S. pyogenes through specific interactions with bacterial surface proteins. In plasma environment, absorption of fibrinogen by S. pyogenes causes a hypocoagulatory state resulting in prolonged clotting times and impaired fibrin network formation. Moreover, the binding of coagulation factors and the subsequent activation of the coagulation system at the bacterial surface lead to the formation of a fibrin network covering S. pyogenes bacteria adhering to epithelial cells. The results suggest that interactions between S. pyogenes and components of the coagulation system contribute to some of the symptoms seen in severe infections caused by this important human pathogen.

Antigens, Bacterial↗

PubMed2002

Bovine anti-Helicobacter pylori antibodies for oral immunotherapy.

BACKGROUND: Passive immunization with orally administered antibodies against specific pathogens has previously been successfully used therapeutically in both animal and human studies. We employed a similar strategy for experimental treatment of mice infected with the gastric pathogen Helicobacter pylori. METHODS: An anti-H. pylori bovine colostral hyperimmune immunoglobulin preparation (BIC) was generated and its efficacy was tested in different in vitro experiments, such as binding to the Lewis(b) blood group antigen, inhibition of adherence of H. pylori to human gastric mucosa tissue sections in situ and in a haemagglutination assay. The BIC preparation was also given in the drinking water to H. pylori-infected mice. RESULTS: An inhibition of 95% of the binding of H. pylori to Lewis(b) glycoconjugate was observed in vitro. Furthermore, a blocking activity of almost 90% was observed when the BIC was preincubated with H. pylori bacteria. Finally, the BIC preparation inhibited the haemagglutination of H. pylori and human red blood cells. Seven of 40 (17.5%) mice remained infected in the treatment group as compared with 25 of 45 (55.5%) in the control group. Hence, the cure rate was 66%, P = < 0.001. The mean number of colonies in the antibody-treated mice where eradication was not successful was also reduced (P < 0.05). In trials using FVB/N transgenic Lewis(b) expressing mice, a cure rate of 50%-66% was observed. CONCLUSION: Bovine colostral antibodies against H. pylori can be generated in high titres, inhibit binding in vitro and can eradicate or reduce the number of bacteria in infected mice.

Animals↗

PubMed2001

Immunoglobulin-binding domains of peptostreptococcal protein L enhance vaginal colonization of mice by Streptococcus gordonii.

Protein L, an immunoglobulin-binding protein of some strains of the anaerobic bacterium Peptostreptococcus magnus, has been hypothesized to be a virulence determinant in bacterial vaginosis. In order to investigate the role of protein L in peptostreptococcal virulence, the Ig-binding domains of protein L were expressed at the surface of the human oral commensal Streptococcus gordonii. Recombinant streptococci were used in vaginal colonization experiments, and protein L-expressing S. gordonii demonstrated enhanced ability to colonize the vaginal mucosa. Compared to the control strain, they also persisted for a longer period in the murine vagina.

Animals↗

PubMed2001

Dermatan sulphate is released by proteinases of common pathogenic bacteria and inactivates antibacterial alpha-defensin.

Defensins represent an evolutionarily conserved group of small peptides with potent antibacterial activities. We report here that extracellular proteinases secreted by the human pathogens Pseudomonas aeruginosa, Enterococcus faecalis and Streptococcus pyogenes release dermatan sulphate by degrading dermatan sulphate-containing proteoglycans, such as decorin. Dermatan sulphate was found to bind to neutrophil-derived alpha-defensin, and this binding completely neutralized its bactericidal activity. During infection, proteoglycan degradation and release of dermatan sulphate may therefore represent a previously unknown virulence mechanism, which could serve as a target for novel antibacterial strategies.

Anti-Bacterial Agents↗

PubMed2001

Unique regulation of SclB - a novel collagen-like surface protein of Streptococcus pyogenes.

Slipped-strand mispairing at sites containing so-called coding repeats (CRs) can lead to phase variation of surface proteins in Gram-negative bacteria. This mechanism, believed to contribute to virulence, has so far not been identified in a Gram-positive bacterium. In the genome of the Gram-positive human pathogen Streptococcus pyogenes, we identified pentanucleotide CRs within a putative signal sequence of an open reading frame (ORF) encoding a novel collagen-like surface protein, denoted SclB. In 12 S. pyogenes strains, the number of CRs in the sclB gene varied from three to 19, rendering the start codon in frame with the downstream ORF in four strains and out of frame in eight strains. A protein reacting with anti-SclB antibodies could only be solubilized from three strains, all containing an intact sclB gene. Variations in the number of CRs were observed within strains of the same M serotype and occurred during growth of S. pyogenes in fresh human blood, but not in medium. The SclB protein has a hypervariable N-terminal part, a collagen-like central part and a typical cell wall sorting sequence containing the LPXTGX motif. SclB is related to the collagen-like SclA and is, like SclA, involved in the adhesion of S. pyogenes bacteria to human cells. However, the Mga protein, known to upregulate sclA and several additional genes encoding virulence factors of S. pyogenes, downregulates sclB transcription. This observation and the potential of SclB to phase vary by slipped-strand mispairing emphasize the unique regulation of this novel S. pyogenes surface protein.

Amino Acid Sequence↗

PubMed2001

Staphylococcus aureus induces release of bradykinin in human plasma.

Staphylococcus aureus is a prominent human pathogen. Here we report that intact S. aureus bacteria activate the contact system in human plasma in vitro, resulting in a massive release of the potent proinflammatory and vasoactive peptide bradykinin. In contrast, no such effect was recorded with Streptococcus pneumoniae. In the activation of the contact system, blood coagulation factor XII and plasma kallikrein play central roles, and a specific inhibitor of these serine proteinases inhibited the release of bradykinin by S. aureus in human plasma. Furthermore, fragments of the cofactor H-kininogen of the contact system efficiently blocked bradykinin release. The results suggest that activation of the contact system at the surface of S. aureus and the subsequent release of bradykinin could contribute to the hypovolemic hypotension seen in patients with severe S. aureus sepsis. The data also suggest that the contact system could be used as a target in the treatment of S. aureus infections.

Bradykinin↗

PubMed2000

Severe lung lesions caused by Salmonella are prevented by inhibition of the contact system.

Vascular damage induced by trauma, inflammation, or infection results in an alteration of the endothelium from a nonactivated to a procoagulant, vasoconstrictive, and proinflammatory state, and can lead to life-threatening complications. Here we report that activation of the contact system by Salmonella leads to massive infiltration of red blood cells and fibrin deposition in the lungs of infected rats. These pulmonary lesions were prevented when the infected animals were treated with H-D-Pro-Phe-Arg-chloromethylketone, an inhibitor of coagulation factor XII and plasma kallikrein, suggesting that inhibition of contact system activation could be used therapeutically in severe infectious disease.

Amino Acid Chloromethyl Ketones↗

PubMed2000

Virulent aggregates of Streptococcus pyogenes are generated by homophilic protein-protein interactions.

Many strains of the important human pathogen Streptococcus pyogenes form aggregates when grown in vitro in liquid medium. The present studies demonstrate that this property is crucial for the adherence, the resistance to phagocytosis and the virulence of S. pyogenes. A conserved sequence of 19 amino acid residues (designated AHP) was identified in surface proteins of common S. pyogenes serotypes. This sequence was found to promote bacterial aggregation through homophilic protein-protein interactions between AHP-containing surface proteins of neighbouring bacteria. A synthetic AHP peptide inhibited S. pyogenes aggregation, reduced the survival of S. pyogenes in human blood and attenuated its virulence in mice. In contrast, mutant bacteria devoid of surface proteins containing AHP-related sequences did not aggregate or adhere to epithelial cells. These bacteria are also rapidly killed in human blood and show reduced virulence in mice, underlining the pathogenic significance of the AHP sequence and S. pyogenes aggregation.

Amino Acid Sequence↗

PubMed2000

Bacterial immunoglobulin superantigen proteins A and L activate human heart mast cells by interacting with immunoglobulin E.

Human heart mast cells (HHMC) have been identified in heart tissue, perivascularly, and in the intima of coronary arteries. In vitro activation of isolated HHMC induces the release of vasoactive and proinflammatory mediators (histamine, tryptase, and cysteinyl leukotriene C(4) [LTC(4)]). We investigated the effects of several bacterial proteins on HHMC activation in vitro. HHMC released histamine, tryptase, and LTC(4) in response to Staphylococcus aureus Cowan 1 and the immunoglobulin (Ig)-binding protein A, but not to S. aureus Wood 46, which does not synthesize protein A. The effect of protein A was inhibited by preincubation with monoclonal IgM V(H)3(+). Some strains of Peptostreptococcus magnus express an Ig light chain-binding surface protein called protein L. Such bacteria and soluble protein L stimulated the release of preformed and newly synthesized mediators from HHMC. Preincubation of HHMC with either protein A or protein L resulted in complete cross-desensitization to a subsequent challenge with the heterologous stimulus or anti-IgE. Monoclonal IgE (kappa chains) blocked protein L-induced release, whereas IgE (lambda chains) had no effect. Streptococcal protein G, formyl-containing tripeptide, and pepstatin A did not activate HHMC. Bacterial products protein A and protein L and intact bacteria (S. aureus and P. magnus) activate HHMC by acting as Ig superantigens.

Adult↗

PubMed2000

SclA, a novel collagen-like surface protein of Streptococcus pyogenes.

Surface proteins of Streptococcus pyogenes are important virulence factors. Here we describe a novel collagen-like surface protein, designated SclA (streptococcal collagen-like surface protein). The sclA gene was identified in silico using the Streptococcal Genome Sequencing Project with the recently identified protein GRAB as the probe. SclA has a signal sequence and a cell wall attachment region containing the prototypic LPXTGX motif. The surface-exposed part of SclA contains a unique NH(2)-terminal domain of 73 amino acids, followed by a collagen-like region. The sclA gene was found to be positively regulated by Mga, a transcriptional activator of several S. pyogenes virulence determinants. A mutant lacking cell wall-associated SclA was constructed and was found to be as effective as wild-type bacteria in platelet aggregation, survival in fresh human blood, and adherence to pharyngeal cells. The sclA gene was found in all 12 S. pyogenes strains that were investigated using PCR. Sequence analysis revealed that the signal sequence and the cell wall attachment region are highly conserved. The collagen-like domain is variable in its NH(2)-terminal region and has conserved repeated domains in its COOH-terminal part. SclA proteins from most strains have additional proline-rich repeats spacing the collagen-like domain and the cell wall attachment sequence. The unique NH(2)-terminal region is hypervariable, but computer predictions indicate a common secondary structure, with two alpha helices connected by a loop region. Immune selection may explain the hypervariability in the NH(2)-terminal region, whereas the preserved secondary structure implies that this region has a common function. These features and the Mga regulation are shared with the M protein of S. pyogenes. Moreover, as with the gene encoding the M protein, phylogenetic analysis indicates that horizontal gene transfer has contributed to the evolution of sclA.

Animals↗

PubMed1999

Protein GRAB of streptococcus pyogenes regulates proteolysis at the bacterial surface by binding alpha2-macroglobulin.

In the molecular interplay between pathogenic microorganisms and their host, proteolytic mechanisms are believed to play a crucial role. Here we find that the important human pathogen Streptococcus pyogenes (group A Streptococcus) expresses a surface protein with high affinity (Ka = 2.0 x 10(8) M-1) for alpha2-macroglobulin (alpha2M), the dominating proteinase inhibitor of human plasma. The immunoglobulin-binding protein G of group C and G streptococci also contains an alpha2M-binding domain and a gene encoding protein GRAB (protein G-related alpha2M-binding protein) was identified in the S. pyogenes Genome Sequencing data base. The grab gene is present in most S. pyogenes strains and is well conserved. Protein GRAB has typical features of a surface-attached protein of Gram-positive bacteria. It also contains a region homologous to parts of the alpha2M-binding domain of protein G and a variable number of a unique 28-amino acid-long repeat. Using Escherichia coli-produced protein GRAB and synthetic GRAB peptides, the alpha2M-binding region was mapped to the NH2-terminal part of protein GRAB, which is the region with homology to protein G. An isogenic S. pyogenes mutant lacking surface-associated protein GRAB showed no alpha2M binding activity and was attenuated in virulence when injected intraperitoneally in mice. Finally, alpha2M bound to the bacterial surface via protein GRAB was found to entrap and inhibit the activity of both S. pyogenes and host proteinases, thereby protecting important virulence determinants from proteolytic degradation. This regulation of proteolytic activity at the bacterial surface should affect the host-microbe relation during S. pyogenes infections.

Amino Acid Sequence↗

PubMed1999

Identification and characterization of a Streptococcus pyogenes ABC transporter with multiple specificity for metal cations.

Metal ions are crucial trace elements for bacteria infecting the human host. The LraI (lipoprotein receptor-associated antigen I) transporter in Streptococcus spp. belongs to the superfamily of ABC transporters. The transporter consists of a lipoprotein, an ATP-binding protein and a hydrophobic integral membrane protein. Here, we describe a new member of the LraI family in the important human pathogen Streptococcus pyogenes. The system was identified in silico by analysis of the S. pyogenes Genome Sequencing Project. The S. pyogenes operon exhibits an atypical organization compared with equivalents in other Streptococcus spp. The presence and atypical organization of the operon was verified in a number of S. pyogenes strains of different serotypes. Transcriptional analysis of the LraI operon demonstrates a polycistronic transcription attenuated by a stable stem-loop structure, which allows the lipoprotein to be expressed in larger quantities than the other two components. The localization of the native lipoprotein at the bacterial surface was shown by proteolytic digestion of S. pyogenes bacteria and NH2-terminal sequencing of a released lipoprotein fragment. Recombinant lipoprotein was expressed as a GST fusion protein, and studies of molecular interactions with metal radioisotopes demonstrated that the protein has affinity for Zn(II), Fe(III) and Cu(II). Zn(II) and Cu(II) were found to compete for the same binding site, whereas Fe(III) uses a second site. Also, proton-induced X-ray analysis of lipoprotein samples identified iron, copper and zinc. Finally, a mutant strain lacking a functional mtsABC operon was generated and showed reduced uptake of 55Fe and 65Zn compared with the wild-type strain. The operon encoding this novel ABC transporter with multiple specificity for metal cations is designated mtsABC, for metal transporter of Streptococcus.

ATP-Binding Cassette Transporters↗

PubMed1999

Protein H, an antiphagocytic surface protein in Streptococcus pyogenes.

Surface-associated M protein is a major virulence factor in Streptococcus pyogenes which confers bacterial resistance to phagocytosis. However, many S. pyogenes strains also express additional structurally related so-called M-like proteins. The strain studied here is of the clinically important M1 serotype and expresses two structurally related surface proteins, the M1 protein and protein H. Mutants were generated that expressed only one or none of these proteins at the bacterial surface. For survival in human blood either protein H or M1 protein was sufficient, whereas the double mutant was rapidly killed. The protein-binding properties of protein H, M1 protein, and the mutants suggest that bacterial binding of immunoglobulin G and factor H or factor H-like protein 1, which are regulatory proteins in the complement system, contribute to the antiphagocytic property.

Antigens, Bacterial↗

PubMed1998

Activation of the contact-phase system on bacterial surfaces--a clue to serious complications in infectious diseases.

Fever, hypotension and bleeding disorders are common symptoms of sepsis and septic shock. The activation of the contact-phase system is thought to contribute to the development of these severe disease states by triggering proinflammatory and procoagulatory cascades; however, the underlying molecular mechanisms are obscure. Here we report that the components of the contact-phase system are assembled on the surface of Escherichia coli and Salmonella through their specific interactions with fibrous bacterial surface proteins, curli and fimbriae. As a consequence, the proinflammatory pathway is activated through the release of bradykinin, a potent inducer of fever, pain and hypotension. Absorption of contact-phase proteins and fibrinogen by bacterial surface proteins depletes relevant coagulation factors and causes a hypocoagulatory state. Thus, the complex interplay of microbe surface proteins and host contact-phase factors may contribute to the symptoms of sepsis and septic shock.

Animals↗

PubMed1998

Treatment of Helicobacter pylori infection in infants in rural Bangladesh with oral immunoglobulins from hyperimmune bovine colostrum.

BACKGROUND: Antibodies from hyperimmune bovine colostrum have been shown to be effective in treatment against a variety of microorganisms, including Helicobacter pylori in adults. AIM: To test this form of treatment in a small group of H. pylori infected children in a periurban community in Bangladesh. METHODS: Twenty-four infants, 4-29 months old (mean age 16.5+/-7.7 months) and infected with H. pylori, were treated with purified immunoglobulins from hyperimmune bovine colostrum for 1 month, in a placebo-controlled, double-blind pilot study. Diagnosis was established with 13C-urea breath test (UBT) before and after the treatment period and at a 1-month follow-up. RESULTS: None of the hyperimmune bovine colostrum-treated children became UBT negative. Five children initially positive in the UBT screening spontaneously became negative by the start of the study with hyperimmune bovine colostrum/placebo. At the end of the 1-month study period, three had became positive again. CONCLUSION: Hyperimmune bovine colostrum does not eradicate H. pylori infection in infants. Transient H. pylori infection is common among infants in high endemic areas, as is reinfection after clearance. This presents obstacles to evaluation of therapeutic investigations in young children in areas where H. pylori is prevalent.

Animals↗

PubMed1998

Production of conjugated linoleic acid by dairy starter cultures.

Nineteen different strains of lactobacilli, lactococci, streptococci and propionibacteria commonly used as dairy starter cultures were tested for their ability to produce conjugated linoleic acid (CLA) from free linoleic acid in vitro. Two strains of Propionibacterium freudenreichii ssp. freudenreichii and one strain of P. freudenreichii ssp. sheramnii were found to be capable of converting free linoleic acid to extracellular CLA. The highest level of CLA formed in the media was 265 micrograms ml-1. Of the different isomers, cis- and trans-9,11-octadecadienoic acid represented more than 70% of the total CLA formed. The inhibitory effect of linoleic acid on the growth of the bacteria and its conversion to CLA in different media by propionibacteria are discussed.

Food Microbiology↗

PubMed1998

Curli, fibrous surface proteins of Escherichia coli, interact with major histocompatibility complex class I molecules.

Curli are thin, coiled fibers expressed on the surface of Escherichia coli that bind several matrix and plasma proteins such as fibronectin, laminin, plasminogen, tissue plasminogen activator, and H-kininogen. In this work, we examined the interactions between curli-expressing E. coli and human major histocompatibility complex class I (MHC-I) and class II (MHC-II) molecules. Curliated E. coli was found to interact with an MHC-I-expressing lymphoma cell line as shown by scanning electron microscopy, whereas the binding to a mutant variant of this cell line expressing small amounts of MHC-I molecules was significantly lower. Moreover, curli-expressing E. coli bound purified radiolabeled MHC-I but not MHC-II molecules, whereas an isogenic curli-deficient mutant strain showed no affinity for either MHC-I or MHC-II. Purified insoluble curli could also bind 125I-labeled MHC-I molecules, and in Western blot experiments the 15-kDa curlin subunit protein bound intact MHC-I molecules as well as beta2-microglobulin, the light chain of MHC-I molecules. A direct interaction between monomeric MHC-I molecules and a bacterial surface protein has previously not been reported. The binding of curli to MHC-I molecules, which are present on virtually all cells in higher vertebrates, will provide curliated E. coli with ample opportunities to interact with a great variety of hosts and host cells. This should facilitate the adaptation of E. coli to different ecological niches, and in human infections the interaction between curli and MHC-I molecules could contribute to adherence and colonization.

Bacterial Adhesion↗

PubMed1998

Identification of an insertion sequence located in a region encoding virulence factors of Streptococcus pyogenes.

An insertion sequence, IS1562, was identified in a Streptococcus pyogenes strain of the clinically important M1 serotype. IS1562 is located in the mga regulon between the genes coding for the M protein and the C5a peptidase, both important virulence factors. The same or similar insertion sequences were found in most S. pyogenes strains, but the chromosomal location differed among isolates.

Adhesins, Bacterial↗