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A Muscholl-Silberhorn

Publications and source records attributed to A Muscholl-Silberhorn.

9 recordsLinked to original sources
PubMed2001

Aggregation substance-mediated adherence of Enterococcus faecalis to immobilized extracellular matrix proteins.

Aggregation substance (AS) of Enterococcus faecalis (E. faecalis), a sex pheromone plasmid encoded cell surface protein, mediates the formation of bacterial aggregates, thereby promoting plasmid transfer. The influence of pAD1-encoded AS, Asa1, on binding to immobilized extracellular matrix proteins was studied. The presence of AS increased enterococcal adherence to fibronectin more than eight-fold, to thrombospondin more than four-fold, to vitronectin more than three-fold, and to collagen type I more than two-fold (P<0.001). In contrast, binding to laminin and collagen type IV occurred independently of AS. Adherence of the constitutively AS expressing E. faecalis OG1X(pAM721) to immobilized fibronectin was found to be approximately five times higher than that of Staphylococcus aureus Cowan and approximately 30 times higher than that of Streptococcus bovis. Investigation of strains with various deletions within the structural gene of asa1 suggests that attachment to immobilized fibronectin is mainly mediated by amino acids within the variable region or by neighbouring residues. Thus, AS may promote adherence to injured epithelium and endothelium, where extracellular matrix proteins are exposed, thereby facilitating colonization and infection.

Bacterial Proteins↗
PubMed2001

Completion of the nucleotide sequence of the Enterococcus faecalis conjugative virulence plasmid pAD1 and identification of a second transfer origin.

pAD1 is a 59.3-kb plasmid in Enterococcus faecalis that has been the subject of intense investigation with regard to its pheromone-inducible conjugation behavior as well as its contribution to virulence. Approximately two-thirds of the pAD1 nucleotide sequence has been previously reported. Here we report on an analysis of the final approximately 22 kb, a significant portion of which is believed to encode structural genes associated with conjugation. The conjugation-related region was also found to contain a new (second) origin of conjugative transfer (oriT). A list of open reading frames covering the entire plasmid is presented.

Conjugation, Genetic↗
PubMed2000

Aggregation substance promotes adherence, phagocytosis, and intracellular survival of Enterococcus faecalis within human macrophages and suppresses respiratory burst.

The aggregation substance (AS) of Enterococcus faecalis, encoded on sex pheromone plasmids, is a surface-bound glycoprotein that mediates aggregation between bacteria thereby facilitating plasmid transfer. Sequencing of the pAD1-encoded Asa1 revealed that this surface protein contains two RGD motifs which are known to ligate integrins. Therefore, we investigated the influence of AS on the interaction of E. faecalis with human monocyte-derived macrophages which constitutively express beta(2) integrins (e.g., CD18). AS was found to cause a greater-than-fivefold increase in enterococcal adherence to macrophages and a greater-than-sevenfold increase in phagocytosis. Adherence was mediated by an interaction between the RGD motif and the integrin CD11b/CD18 (complement receptor type 3) as demonstrated by inhibition studies with monoclonal antibodies and RGD peptide. AS-bearing enterococci were significantly more resistant to macrophage killing during the first 3 h postinfection, probably due to inhibition of the respiratory burst as indicated by reduced concentrations of superoxide anion.

Bacterial Adhesion↗
PubMed1999

Cloning and functional analysis of Asa373, a novel adhesin unrelated to the other sex pheromone plasmid-encoded aggregation substances of Enterococcus faecalis.

pAM373 of Enterococcus faecalis deviates from the various other representatives of sex pheromone plasmids in that it encodes a clumping-mediating adhesin, Asa373, unrelated to the highly conserved aggregation substances typical of this plasmid class. The use of a new general cloning strategy and sequencing of the corresponding gene has confirmed that Asa373 represents a novel type of adhesin embedded in a DNA sequence very similar to sex pheromone plasmid pPD1. To prove the specific function of the relatively small protein (75.6 kDa vs 137 kDa for pAD1-encoded Asa1) in cell aggregation, an expression vector, pERM-ex1, was constructed, allowing reliable and stable expression of proteins in E. faecalis. The expression of Asa373 in E. faecalis indeed resulted in constitutive clumping, whereas non-polar disruption of the gene in the original pAM373 abolished clumping capacity. Expression in a strain (INY3000) defective in binding substance - which for the other aggregation substances constitutes the attachment site on the mating partner - did not alter Asa373-dependent clumping; this implies a separate mechanism in cell-cell interaction for this adhesin. Some amino acid motifs of Asa373 link the protein to adhesins of oral streptococci and other cell surface proteins. Comparison of the leader sequence of asa373 with those of several other aggregation substances revealed a highly conserved translational unit possibly involved in the regulation of asa373 expression.

Adhesins, Bacterial↗
PubMed1998

Analysis of the clumping-mediating domain(s) of sex pheromone plasmid pAD1-encoded aggregation substance.

Aggregation substance, a cell surface adhesin encoded on sex-pheromone plasmids exclusively found in the opportunistic pathogen Enterococcus faecalis, displays a dual function in that it mediates (a) adhesion to host tissues and (b) aggregation of E. faecalis cells to result in efficient plasmid transfer. While there have been many investigations regarding the regulation of inducible plasmid transfer and involvement in pathogenicity, nearly nothing is known about the structural basis of clumping capacity intrinsic to aggregation substance. Here, data are presented regarding the respective domain(s) of Asa1 (the adhesin encoded on plasmid pAD1) by analyzing the effects of in-frame deletions on clumping and by measuring binding of E. faecalis cells to surface-bound subfragments of aggregation substance. These data indicate that the N-terminal part of the adhesin is responsible for clumping, with a region between amino acid 525 and amino acid 617 playing a dominant role. Furthermore, by raising antibodies against different fragments of Asa1, it is shown that aggregation substance contains cross-reacting epitopes in its C-terminal and N-terminal parts, which could not be derived from their primary sequences.

Bacterial Proteins↗
PubMed1998

Enterococcus faecalis gene transfer under natural conditions in municipal sewage water treatment plants.

The ability of Enterococcus faecalis to transfer various genetic elements under natural conditions was tested in two municipal sewage water treatment plants. Experiments in activated sludge basins of the plants were performed in a microcosm which allowed us to work under sterile conditions; experiments in anoxic sludge digestors were performed in dialysis bags. We used the following naturally occurring genetic elements: pAD1 and pIP1017 (two so-called sex pheromone plasmids with restricted host ranges, which are transferred at high rates under laboratory conditions); pIP501 (a resistance plasmid possessing a broad host range for gram-positive bacteria, which is transferred at low rates under laboratory conditions); and Tn916 (a conjugative transposon which is transferred under laboratory conditions at low rates to gram-positive bacteria and at very low rates to gram-negative bacteria). The transfer rate between different strains of E. faecalis under natural conditions was, compared to that under laboratory conditions, at least 10(5)-fold lower for the sex pheromone plasmids, at least 100-fold lower for pIP501, and at least 10-fold lower for Tn916. In no case was transfer from E. faecalis to another bacterial species detected. By determining the dependence of transfer rates for pIP1017 on bacterial concentration and extrapolating to actual concentrations in the sewage water treatment plant, we calculated that the maximum number of transfer events for the sex pheromone plasmids between different strains of E. faecalis in the municipal sewage water treatment plant of the city of Regensburg ranged from 10(5) to 10(8) events per 4 h, indicating that gene transfer should take place under natural conditions.

Enterococcus faecalis↗
PubMed1997

Why does Staphylococcus aureus secrete an Enterococcus faecalis-specific pheromone?

The long known fact that Staphylococcus aureus can secrete a peptide (staph-cAM373) which acts as a sex pheromone for strains of E. faecalis carrying the sex pheromone plasmid pAM373 was studied in detail. 85 of 100 independent isolates of S. aureus produced an activity inducing the pAM373 encoded adhesin resulting in a clumping reaction of E. faecalis (i.e. secreted staph-cAM373), but not a single one of 100 independent isolates of coagulase-negative Staphylococci possessed this activity. The production of peptides acting as sex pheromone for E. faecalis was observed only for sex pheromone plasmid pAM373, but not for sex pheromone plasmids pAD1 and pPD1. It was shown that the amount of staph-pAM373 produced during growth paralleled cell mass, therefore this peptide should not be used as a cell density indicator by S. aureus (i.e. has no quorum sensing function). The potential function of staph-cAM373 to trigger gene transfer from Escherichia faecalis to S. aureus is discussed.

Bacterial Adhesion↗