Establishment of a Cre recombinase based mutagenesis protocol for markerless gene deletion in Streptococcus suis

The lack of knowledge about pathogenicity mechanisms of Streptococcus (S.) suis is, at least partially, attributed to limited methods for its genetic manipulation. Here, we established a Cre-lox based recombination system for markerless gene deletions in S. suis serotype 2 with high selective pressure and without undesired side effects.

Establishment of a model of Streptococcus iniae meningoencephalitis in Nile tilapia (Oreochromis niloticus)

Streptococcus iniae is an invasive pathogen causing meningitis and other lesions in various fish species. Furthermore, S. iniae is an emerging zoonotic agent that causes cellulitis in man. The aims of this study were to establish an intraperitoneal infection model for S. iniae in Nile tilapia (Oreochromis niloticus) and to develop a new histopathological scoring system to reflect the degree and extent of inflammation as well as the presence of necrosis in the brain and eye. Intraperitoneal administration of 10(6) colony-forming units (CFU) led to 80% mortality and numerous fish developing clinical signs of central nervous system dysfunction. Microscopical examination of four regions of the brain (olfactory bulb, cerebellum, cerebrum and optical lobe) and the eye revealed the presence of lymphohistiocytic leptomeningitis, meningoencephalitis and endophthalmitis. Lesions were dominated by macrophages that often contained intracellular bacteria. Necrosis was recorded in some cases. Bacteriological screening revealed that multiple organs, including brain and eye, were infected with S. iniae and S. iniae colonized the scales and gills in high number. S. iniae was detected in tank water during the first week post infection, suggesting that infected tilapia might shed up to 3 × 10(7) CFU of S. iniae within 24 h. A multiplex polymerase chain reaction allowed confirmation of the challenge strain by detection of the virulence factors simA, scpI, cpsD, pgi, pgm and sagA.

Role of glucose and CcpA in capsule expression and virulence of Streptococcus suis

Streptococcus suis is one of the most important pathogens in pigs and is also an emerging zoonotic agent. After crossing the epithelial barrier, S. suis causes bacteraemia, resulting in meningitis, endocarditis and bronchopneumonia. Since the host environment seems to be an important regulatory component for virulence, we related expression of virulence determinants of S. suis to glucose availability during growth and to the sugar metabolism regulator catabolite control protein A (CcpA). We found that expression of the virulence-associated genes arcB, representing arcABC operon expression, cps2A, representing capsular locus expression, as well as sly, ofs, sao and epf, differed significantly between exponential and early stationary growth of a highly virulent serotype 2 strain. Deletion of ccpA altered the expression of the surface-associated virulence factors arcB, sao and eno, as well as the two currently proven virulence factors in pigs, ofs and cps2A, in early exponential growth. Global expression analysis using a cDNA expression array revealed 259 differentially expressed genes in early exponential growth, of which 141 were more highly expressed in the CcpA mutant strain 10ΔccpA and 118 were expressed to a lower extent. Interestingly, among the latter genes, 18 could be related to capsule and cell wall synthesis. Correspondingly, electron microscopy characterization of strain 10ΔccpA revealed a markedly reduced thickness of the capsule. This phenotype correlated with enhanced binding to porcine plasma proteins and a reduced resistance to killing by porcine neutrophils. Taken together, our data demonstrate that CcpA has a significant effect on the capsule synthesis and virulence properties of S. suis.

Isolation and characterization of a haemolysin from Trichophyton mentagrophytes

Haemolytic activities of Trichophyton (T.) mentagrophytes were detected and characterized by qualitative and quantitative assays. On Columbia agar supplemented with blood from horses, cattle or sheep, T. mentagrophytes expressed a strong zone of complete haemolysis. No haemolytic activities could be detected in the closely related T. verrucosum var. ochraceum. The same results were obtained after cultivation of the fungi on sterile cellulose acetate filters placed on the surface on Columbia blood agar. After removal of the filter, complete haemolysis was detected below the colony of T. mentagrophytes. A soluble haemolysin from culture supernatant of this strain was isolated and partially purified. Specific haemolytic activity per mg protein was enriched 2.6-fold in filtrate F(1), a fraction obtained as filtrate after filtration through 3kDa cut-off membranes. The partially purified haemolysin was neither affected by proteinase K treatment, nor by high and low temperatures, suggesting that it represents a small peptide haemolysin. Accordingly, in a commercial enzymatic activity test only the crude culture filtrate, but none of the subsequent purification fractions showed reactivity. Evaluation of the specificity of the haemolysin using erythrocytes from different mammalian species revealed that sensitivity was highest to those of equines, followed by erythrocytes from sheep, cattle, swine, dogs and humans. None of the erythrocytes was lysed by filtrate F(1) from T. verrucosum var. ochraceum. Furthermore, different eukaryotic cell lines from different species were tested in their sensitivity to cytolytic activities of the haemolysin, but no membrane damage could be detected.

Adherence of Streptococcus suis to Porcine Endothelial Cells

Streptococcus suis can cause invasive diseases in pigs and humans, such as meningitis or arthritis. Adherence to and invasion of endothelial cells might represent important steps in survival and spread of S. suis within the host. We tested in vitro adherence and invasion of S. suis strains using a porcine brain microvascular and aortal endothelial cell line. Four S. suis strains were tested with and without prior treatment with porcine serum containing anti-S. suis antibodies. Strains included a capsular serotype 2 strain and its non-encapsulated isogenic mutant strain, as well as two non-typeable (NT) strains, which expressed no capsule under our experimental conditions. Strains adhered to both cell lines to different extents depending on encapsulation and pre-treatment with porcine immune serum. The serotype 2 strain showed almost no adherence, whereas the non-encapsulated mutant strain adhered strongly. Similarly, both NT strains adhered substantially better than the serotype 2 strain. Pre-treatment of bacteria with porcine serum increased adherence of the encapsulated serotype 2 strain and decreased adherence of the non-encapsulated strains. None of the strains was able to efficiently invade either of the two cell lines, except for one NT strain, which showed a very low extend of invasion. Our results suggest that S. suis can adhere to but not invade porcine endothelial cells, and that this interaction may involve different bacterial surface structures, such as capsular polysaccharides and/or binding sites for serum components.

Effects of subinhibitory concentrations of florfenicol on morphology, growth, and viability of Staphylococcus aureus

Staphylococcus aureus strain Newman was investigated for changes in its growth pattern, its morphology and its viability when grown in the presence of 3 microg/ml florfenicol (Ff). This concentration corresponds to the 0.75-fold strain-specific minimum inhibitory concentration (MIC). Under these conditions, S. aureus Newman showed a distinct retardation in its growth pattern and 20% dead cells were detected in a fluorescence microscopic viability assay. However, bactericidal activity - defined as a 3-log drop in the staphylococcal population - was not recorded at this Ff concentration. Further analysis of the cell wall revealed a significant increase in cell wall thickness of S. aureus Newman when grown in the presence of 3 microg/ml Ff. This might result in a compression of the protoplast with subsequent disruption of single staphylococcal cells. Accordingly, 20% of the staphylococcal cells analysed by electron microscopy proved to be disrupted. These observations suggest that Ff can cause a thickening of the cell wall accompanied by impaired viability of the staphylococcal cells.

Immunogenicity of Murein-associated Proteins from Temperature-stressed Streptococcus suis Cultures

We compared immunogenicity in pigs of whole cell lysate proteins (WCP) with murein-associated proteins (MAP) obtained from a virulent serotype 2 strain of Streptococcus (S.) suis grown at 32 or 42 degrees C. Protein fractions were tested for their ability to induce antibodies in 3-week-old piglets by enzyme-linked immunosorbent assay and Western blot analysis. We found a significant increase in the antibody levels in all sera irrespective of the preparation used for immunization. However, alpha-WCP sera showed higher reactivities than alpha-MAP sera, and piglets immunized with 32 degrees C preparations (alpha-32 sera) showed higher responses than those immunized with 42 degrees C preparations (alpha-42 sera). Western blot analysis revealed that alpha-WCP sera in part reacted with different proteins when compared with alpha-MAP sera. Furthermore, some proteins were only detected by alpha-32 but not by alpha-42 sera. In conclusion, the results demonstrate the immunogenicity of cell wall MAP of S. suis, and highlight the importance of considering growth conditions in the preparation of subunit vaccines.

Non-encapsulated strains reveal novel insights in invasion and survival of Streptococcus suis in epithelial cells

Streptococcus suis is a porcine and human pathogen causing invasive diseases, such as meningitis or septicaemia. Host cell interactions of S. suis have been studied mainly with serotype 2 strains, but multiple capsular serotypes as well as non-typeable strains exist with diverse virulence features. At present, S. suis is considered an extracellular pathogen. However, whether or not it can also invade host cells is a matter of controversial discussions. We have assessed adherence and invasion of S. suis for HEp-2 epithelial cells by comparing 10 serotype 2 strains and four non-typeable (NT) strains. Only the NT strains and a non-encapsulated serotype 2 mutant strain, but none of the serotype 2 strains, adhered strongly and were invasive. Invasion seemed to be affected by environmental signals, as suggested from comparison of strains grown in different media. Further phenotypic and genotypic characterization revealed a high diversity among the different strains. Electron microscopic analysis of invasion of selected invasive NT strains indicated different uptake mechanisms. One strain induced large invaginations comparable to those seen in 'caveolae' mediated uptake, whereas invasion of the other strains was accompanied by formation of filipodia-like membrane protrusions. Invasion of all strains, however, was similarly susceptible to hypertonic sucrose, which inhibits receptor-mediated endocytosis. Irrespective of the uptake pathway, streptococci resided in acidified phago-lysosome like vacuoles. All strains, except one, survived intracellularly as well as extracellular acidic conditions. Survival seemed to be associated with the AdiS protein, an environmentally regulated arginine deiminase of S. suis. Concluding, invasion and survival of NT strains of S. suis in epithelial cells revealed novel evidence that S. suis exhibits a broad variety of virulence-associated features depending on genetic variation and regulation.

[Occurrence and diagnostic relevance of virulence-associated factors in Streptococcus suis]

Streptococcus suis (Sc. suis) can cause very different clinical entities. In contrast to Sc. suis-associated pneumonia, the induction of meningitis, septicemia, and polyarthritis by certain Sc. suis strains requires the expression of virulence factors that contribute to the invasiveness of the pathogen. In the presented study, we examined the occurrence of known virulence-associated factors in Sc. suis isolates from samples sent to the Institute of Microbiology, School of Veterinary Medicine Hannover, in order to evaluate their significance as potential virulence factors in different disease complexes in Northern Germany. The results show that (i) MRP + EF + serotype 2 and MRP* EF-serotype 9 strains are statistically significant associated with the disease complex meningitis/septicemia/arthritis and, thus, have to be considered invasive strains, (ii) serotyping alone is not sufficient for identification of virulent strains, (iii) there is a remarkable heterogeneity among pneumonia-associated Sc. suis strains and (iv) activity of haemolysin or suilysin appears to be not appropriate as virulence marker. Finally, it has to be noted that at present only half of the Sc. suis isolates from pigs with meningitis/septicemia/poyarthritis can be characterised by the detection of virulence-associated factors. Thus, the identification and characterisation of additional, serotype independent virulence factors of Sc. suis is a very important issue in future studies.

[Pathogenesis and immune reactions of paratuberculosis]

Mycobacterium avium subspecies paratuberculosis (M. ptb) is known as the cause of paratuberculosis for over a century but the knowledge on biology of the organism and pathogenesis of the disease is still limited. There are several reasons for the present lack of progress, these are (i) the extremely slow growth of the bacterium, a feature which has also protected the organism against researchers, (ii) confusion over its taxonomy and identification, (iii) limited possibilities for the application of molecular biology techniques, and (iv) the extremely long incubation period in natural infection for which no suitable laboratory model exists. Despite these discouraging facts, recent research efforts have led to important findings, which have shown that a better understanding of the disease may contribute to the improvement of control strategies. This presentation focuses mainly on the unique nature of M. ptb within the mycobacteria and the central role of the macrophage in pathogenesis and immune response. More details can be found in a number of excellent recent reviews (see list of references).

Toxin types of Clostridium perfringens isolated from free-ranging, semi-domesticated reindeer in Norway

Samples of faeces were taken from 166 healthy domesticated reindeer (Rangifer tarandus tarandus) from three flocks in different reindeer husbandry districts in northern Norway and examined bacteriologically for the presence of Clostridium perfringens. The organism was isolated from 98 (59 per cent) of the reindeer. The isolates were classified into C perfringens toxin types by PCR analysis specific for the genes encoding the four major toxins (alpha, beta, epsilon and tau) and were subclassified by the detection of the genes encoding C perfringens beta2-toxin and enterotoxin. All the isolates belonged to C perfringens toxin type A. In addition, 15 of the 98 isolates were PCR-positive for the beta2-toxin gene, and two of the isolates had the the gene encoding for enterotoxin.

Characterization of the intracellular survival of Mycobacterium avium ssp. paratuberculosis: phagosomal pH and fusogenicity in J774 macrophages compared with other mycobacteria

The phagosomes containing viable pathogenic mycobacteria, such as Mycobacterium (M.) tuberculosis and Mycobacterium avium ssp. avium (M. avium), are known to be limited in their ability to both acidify and fuse with late (but not early) endocytic organelles. Here, we analysed the pH and fusogenicity of phagosomes containing M. avium ssp. paratuberculosis (M. ptb), the causative agent of paratuberculosis in ruminants. Using the murine J774 macrophage cell line, we compared viable and heat-killed M. ptb and, in addition, viable or dead M. avium, as well as two non-pathogenic mycobacteria, Mycobacterium smegmatis and Mycobacterium gordonae. Electron microscopic analysis revealed that M. ptb persisted intracellularly in phagosomes for up to 15 days. The phagosomes containing live M. ptb and M. avium were significantly reduced in their ability to acquire some markers for the endocytic pathway, such as internalized calcein, BSA-gold or the membrane protein Lamp 2. However, they were almost completely accessible to 70 kDa fluorescein isothiocyanate (FITC)-dextran and Lamp 1. Overall, the phagosomes containing dead pathogenic mycobacteria behaved similarly to the ones containing live non-pathogenic mycobacteria in all experiments. Using FITC-dextran in a novel fluorescence-activated cell sorting (FACS)-based method, we could also show that the bulk of endocytic compartments, including phagosomes, were only very mildly acidified to approximately pH 6.3 over at least 72 h in J774 cells infected with live M. ptb and M. avium. In contrast, J774 cells treated with heat-killed M. ptb or BSA-coated latex beads showed substantial acidification of the phagosome/endocytic compartments to a pH value of approximately 5.2. After infection with M. smegmatis and M. gordonae, acidification was initially (1-5 h after infection) inhibited, but increased after longer infection to levels similar to those with dead mycobacteria.

Differential changes in heat shock protein-, lipoarabinomannan-, and purified protein derivative-specific immunoglobulin G1 and G2 isotype responses during bovine Mycobacterium avium subsp. paratuberculosis infection

Bovine paratuberculosis is caused by infection of young calves with Mycobacterium avium subsp. paratuberculosis. In some of the chronically infected cows the long asymptomatic stage (2 to 4 years) is followed by a rapid progression to a clinical stage due to protein-losing enteropathy, which will ultimately be fatal. The current dogma is that in early stages of disease the cell-mediated responses predominate, whereas in the clinical stage of the disease the humoral responses prevail, possibly signaling a switch in immune reactivity related to disease progression. We developed immunoglobulin M (IgM)-, IgA-, and IgG1- and IgG2-isotype-specific enzyme-linked immunosorbent assays for M. avium subsp. paratuberculosis-derived antigens (heat shock proteins of 70 kDa [Hsp70] and 65 kDa [Hsp65], lipoarabinomannan [LAM], and M. avium subsp. paratuberculosis purified protein derivative PPD [PPDP]). The serological responses of cows in different stages of paratuberculosis were used to evaluate the putative shift in immune responsiveness. In the clinical stage the PPDP-specific IgG1 responses were increased compared to those in the asymptomatic stage. However, total IgG1 and IgG2 and the Hsp70-, Hsp65-, and LAM-specific isotype responses were decreased in the clinical stage were decreased compared to those in the asymptomatic stage of disease. Thus, the classical pattern was found only for PPDP antigens and the IgG1 isotype. For other antigens and isotypes and the total IgG levels, the response pattern is different and indicates that there is no uniform association with increased antibody responses during the progression from the asymptomatic stage to the clinical stage of bovine paratuberculosis.

Relatedness of Streptococcus suis isolates of various serotypes and clinical backgrounds as evaluated by macrorestriction analysis and expression of potential virulence traits

We evaluated the genetic diversity of Streptococcus suis isolates of different serotypes by macrorestriction analysis and elucidated possible relationships between the genetic background, expression of potential virulence traits, and source of isolation. Virulence traits included expression of serotype-specific polysaccharides, muramidase-released protein (MRP), extracellular protein factor (EF), hemolysin activity, and adherence to epithelial cells. Macrorestriction analysis of streptococcal DNA digested with restriction enzymes SmaI and ApaI allowed differentiation of single isolates that could be assigned to four major clusters, named A1, A2, B1, and B2. Comparison of the genotypic and phenotypic features of the isolates with their source of isolation showed that (i) the S. suis population examined, which originated mainly from German pigs, exhibited a genetic diversity and phenotypic patterns comparable to those found for isolates from other European countries; (ii) certain phenotypic features, such as the presence of capsular antigens of serotypes 2, 1, and 9, expression of MRP and EF, and hemolysin activity (and in particular, combinations of these features), were strongly associated with the clinical background of meningitis and septicemia; and (iii) isolates from pigs with meningitis and septicemia showed a significantly higher degree of genetic homogeneity compared to that for isolates from pigs with pneumonia and healthy pigs. Since the former isolates are considered highly virulent, this supports the theory of a clonal relationship among highly virulent strains.

Pathogenesis of Mycobacterium avium subspecies paratuberculosis infections in ruminants: still more questions than answers

Mycobacterium avium subspecies paratuberculosis is the etiologic agent of paratuberculosis (Johnes disease), a chronic enteritis in ruminants, which is one of the most widespread bacterial diseases of domestic animals, causing enormous economic losses worldwide. Though the disease was first described more than a century ago, the biology of the infecting organism and the mechanisms of its interactions with the host still remain a mystery. In this review, recent advances made on pathogenesis of paratuberculosis are summarized and future challenges are discussed.

Differential induction of NO synthesis by gram-positive and gram-negative bacteria and their components in bovine monocyte-derived macrophages

The ability of Gram-positive and Gram-negative bacteria to promote the induction of NO synthesis in bovine monocyte-derived macrophages (MDM) was tested. Heat-killed Gram-negative organisms induced NO synthesis at low concentrations (optimum 0.2 to 2 microg/ml wet weight), regardless of the strain, and the response was only moderately enhanced by co-administration of recombinant bovine interferon-gamma (rboIFN-gamma). The activity was largely, but not exclusively, due to lipopolysaccharide (LPS), since it was largely abrogated by co-incubation with polymyxin-B. Diphosphoryl-lipid-A and rough-strain LPS were two orders of magnitude more active than monophosphoryl-lipid A, but two orders of magnitude less active than smooth-strain LPS, suggesting that O side chains contribute to increasing the affinity of LPS or to act as a costimulus. Gram-positive bacteria as single stimuli were four orders of magnitude less potent in inducing NO synthesis than Gram-negative organisms, but upon costimulation with rboIFN-gamma, some of them were excellent inducers of NO synthesis. A similar rboIFN-gamma-enhanced NO synthesis induction was also observed for zymosan, muramyl dipeptide, lipoteichoic acid and lipoarabinomannan, although to a lesser extent than for the whole heat-inactivated prototypic organisms. Thus, bovine macrophages exposed to rboIFN-gamma have mechanisms by which they universally react to bacterial compounds distinct from LPS by induction of NO synthesis.

[Bovine paratuberuclosis: history and resulrs of new efforts to control an old disease]

The problem of bovine paratuberculosis is being reviewed. The historic development as well as the cultivation and characterization of the infectious agent are described. The current knowledge of the epidemiology is being discussed with particular emphasis on excretion and resistance of the bacterium, potential hosts, and transmission pathways. Subsequently, the economic importance of the disease is described from an international and a German point of view. International, European and German regulations on para tuberculosis are discussed with respect to their possible influence on future development of animal trade politics.

Identification and characterization of a novel extracellular ferric reductase from Mycobacterium paratuberculosis

A novel extracellular mycobacterial enzyme was identified in the ruminant pathogen Mycobacterium paratuberculosis. The enzyme was capable of mobilizing iron from different sources such as ferric ammonium citrate, ferritin, and transferrin by reduction of the metal. The purified reductase had a calculated Mr of 17,000, was sensitive to proteinase K treatment, and had an isoelectric point of pH 9. Analysis of the amino acid composition revealed glycine, serine, asparagine (or aspartic acid), and glutamine (or glutamic acid) as the most frequently occurring residues. Enzymatic activity was highest at 37 degrees C and between pH 5 and 10. The calculated Km and Vmax for ferric ammonium citrate were 0.213 mM and 0.345 mM min(-1) mg(-1), respectively. Using a specific antireductase antibody in immunoelectron microscopy, we were able to detect the enzyme associated with intracellular mycobacteria in naturally M. paratuberculosis-infected bovine tissue. We prepose that the reductase of M. paratuberculosis represents an alternative strategy of mycobacteria to mobilize ferric iron and discuss its potential role in bacterial evasion of intracellular defense mechanisms.

The fibronectin-binding protein of Streptococcus pyogenes, SfbI, is involved in the internalization of group A streptococci by epithelial cells

Streptococcus pyogenes organisms (group A streptococci) are considered to be highly adhesive extracellular pathogens. However, it has recently been reported that S. pyogenes has the capacity to efficiently invade eukaryotic cells. In this study, we demonstrate that the interaction of S. pyogenes fibronectin-binding protein (SfbI) with fibronectin on nonphagocytic HEp-2 cells triggers bacterial internalization. Blocking of the SfbI adhesin by either antibodies against the whole protein or antibodies against the fibronectin-binding domains of SfbI, as well as pretreatment of HEp-2 cells with purified SfbI protein, prevents both S. pyogenes attachment and internalization. Inert latex beads precoated with the purified SfbI protein are ingested by eukaryotic cells, demonstrating that SfbI is per se enough to trigger the internalization process. Experiments performed with a recombinant SfbI domain encompassing the two fibronectin-binding regions of the SfbI molecule demonstrated that these binding regions are essential and sufficient to activate uptake by HEp-2 cells. These results demonstrate that the fibronectin-binding protein SfbI is involved in both S. pyogenes' attachment to and ingestion by HEp-2 cells and contribute to elucidation of the underlying molecular events leading to eukaryotic cell invasion by S. pyogenes.

Characterization of group B streptococcal invasion in HEp-2 epithelial cells

The invasion of group B streptococci (GBS) in HEp-2 epithelial cells was analyzed by electron microscopy and a quantitative antibiotic survival assay. Invasion of GBS involved intimate attachment of streptococcal chains, engulfment of the adherent bacteria by cellular protrusions, entry of the bacteria in a 'polar' fashion and formation of membrane-bound vacuoles in which most of the intracellular streptococci resided. At later stages of infection bacteria were also found free in the cytoplasm. Efficient uptake of streptococci by HEp-2 cells occurred within 20 min and live intracellular bacteria were detectable up to 48 h post-infection. Invasion of GBS required activation of the eukaryotic actin microfilament system involving, at least partially, protein kinase signal transduction pathways. Invasion was inhibited in a dose-dependent manner by decreasing extracellular Ca2+ levels as well as by substances known to interfere with eukaryotic calcium regulatory systems. These results suggest that GBS invade HEp-2 cells by triggering calcium-dependent phagocytosis-like internalization mechanisms and persist intracellularly both in vacuoles and free in the cytoplasm.

Entry and intracellular survival of group B streptococci in J774 macrophages

The mouse macrophage-like cell line J774 was used to analyze opsonin-independent entry and survival of group B streptococci (GBS). Efficient entry of GBS in J774 cells occurred within 5 min postinfection, and streptococci persisted intracellularly without loss of viability for at least 8 h. At 24 h postinfection, 30% of the total intracellular GBS was recovered from macrophages. Inhibition studies using different biochemical modulators of cellular functions showed that bacterial entry seemed to involve nonglycosylated J774 surface structures different from known receptors such as fibronectin-binding integrins. Internalization of GBS by J774 cells occurred by a microfilament-dependent phagocytosis-like process also involving participation of receptor-mediated endocytosis. Prior opsonization of GBS with human serum containing anti-GBS antibodies did not affect bacterial entry but significantly reduced the intracellular survival of GBS. Transmission electron microscopic analysis confirmed these findings and demonstrated that both opsonized and nonopsonized bacteria were contained within phagosomes during the whole infection period. Transmission electron microscopy further revealed that decreased intracellular survival rates of opsonized GBS appeared to be due to increased lysosomal activities of the macrophages. These results suggest that in the absence of opsonins, GBS are able to enter and persist efficiently in macrophages by evading intracellular antibacterial activities commonly associated with opsonin-mediated uptake.

Identification of an immunoglobulin A binding motif located in the beta-antigen of the c protein complex of group B streptococci

The beta-antigen of the c protein complex of group B streptococci contains two immunoglobulin A (IgA)-binding domains called A and B. A 73-amino-acid segment in domain A is responsible for most of the IgA-binding activity. To identify the IgA binding motif, the 73-amino-acid domain was divided into 60 14-amino-acid overlapping peptides spot synthesized onto a cellulose membrane. A 20-residue putative antigenic epitope was identified and expressed as a fusion protein. The fusion protein was purified by fast protein liquid chromatography and used to raise rabbit antiserum. By use of a membrane with spot-synthesized peptide amino acids of decreasing length (from 14 to 6 amino acids), the major antigenic epitope recognized by the anti-fusion protein antibodies was mapped to motif MLKKIE. Anti-fusion protein antibodies inhibited the binding of IgA to group B streptococci. This inhibition could be blocked by the peptide containing the motif MLKKIE. These results indicate that the motif MLKKIE is located in the IgA-binding site. The IgA-binding domain of beta-antigen from three group B streptococcal strains reacted with the anti-fusion protein antibodies, and their coding sequences gave positive signals in Southern hybridization. The sequences of beta-antigen from these strains were amplified by PCR, and sequence analysis showed them to be identical. The results indicate that the motif MLKKIE is required for IgA binding and is present in different group B streptococcal strains.

Correlation of epithelial cell invasiveness of group B streptococci with clinical source of isolation

Neonatal infections caused by Group B streptococci (GBS) may lead to pneumonia, sepsis, or meningitis indicating that GBS are able to invade tissues and enter the bloodstream from infected sites. In this study, we showed that the tissue invasiveness of GBS may be related to their ability to invade epithelial cells in vitro by correlating the degree of GBS invasion of cultured human respiratory epithelial cells with the clinical source of isolation. Among 77 isolates tested, those from invasive infections of neonates and adults were significantly (P < 0.001) more invasive than those from vaginal carriers and colonised neonates without clinical symptoms. Furthermore, isolates from the blood were more invasive (P < 0.05) than those from other sites. GBS invasion seemed to be mediated by bacterial surface proteins since trypsin treatments of streptococci significantly reduced their invasion into epithelial cells and invasiveness was not limited to a certain capsular serotype. The two major GBS surface protein antigens c and R, however, were not involved in the invasion process. These results indicate that in vitro invasion of cultured human cells reflects the in vivo invasive property of GBS and involves bacterial surface components different from known virulence factors such as capsule or protein antigens c and R.

The fibronectin binding domain of the Sfb protein adhesin of Streptococcus pyogenes occurs in many group A streptococci and does not cross-react with heart myosin

Sfb protein, a fibronectin binding adhesin of Streptococcus pyogenes (Lancefield group A streptococcus), mediates streptococcal adherence to human epithelial cells via its fibronectin binding domain coded by a repetitive gene region named fnbr. In the present study, Southern blot analysis using the fnbr gene region as a probe to screen genomic DNA from 51 epidemiologically unrelated clinical isolates of S. pyogenes revealed that 70% carried a sequence homologous to the fnbr probe. Among ten other streptococcal strains belonging to serological groups B, C, and G, DNA from only two human S. equisimilis (group C) strains reacted with the probe. Further analysis by PCR-mediated amplification of the binding repeat coding sequences revealed that repeats of different S. pyogenes isolates were identical in size but varied in number, ranging from one to five. Most of the isolates were shown to carry multiple repeats. Presence of the probe-positive sequence correlated strongly with streptococcal binding to purified fibronectin and adherence to HEp2 human epithelial cells; of the 36 probe-positive isolates, 95% bound fibronectin and 89% adhered strongly to epithelial cells, whereas among the 15 probe-negative isolates only 27% had binding activities for fibronectin and 27% showed strong adherence to HEp2 cells. Antibodies raised against the fibronectin binding domain of Sfb protein recognized streptococcal fibronectin binding surface proteins in most of the clinical isolates but did not react with heart or skeletal muscle myosin in an enzyme immunoassay, as is the case with antibodies directed to M protein, another major surface protein of group A streptococci. The results of the present study suggest that Sfb protein could be a potential candidate for a streptococcal vaccine.

Domain structure and conserved epitopes of Sfb protein, the fibronectin-binding adhesin of Streptococcus pyogenes

Streptococcus pyogenes expresses a fibronectin-binding surface protein (Sfb protein) which mediates adherence to human epithelial cells. The nucleotide sequence of the sfb gene was determined and the primary sequence of the Sfb protein was analysed. The protein consists of 638 amino acids and comprises five structurally distinct domains. The protein starts with an N-terminal signal peptide followed by an aromatic domain. The central part of the protein is formed by four proline-rich repeats which are flanked by non-repetitive spacer sequences. A second repeat region, consisting of four repeats that are distinct from the proline repeats and have been shown to form the fibronectin-binding domain, is located in the C-terminal part of the protein. The protein ends with a typical cell wall and membrane anchor region. Comparative sequence analysis of the N-terminal aromatic domain revealed similarities with carbohydrate-binding sites of other proteins. The proline repeat region of the Sfb protein shares characteristic features with proline-rich repeats of functionally distinct surface proteins from pathogenic Gram-positive cocci. Immunoelectron microscopy revealed an even distribution of the fibronectin-binding domain of Sfb protein on the surface of streptococcal cells. Analyses of 38 sfb genes originating from different S. pyogenes isolates revealed primary sequence variability in regions coding for the N-termini of mature Sfb proteins, whereas sequences coding for the central and C-terminal repeats were highly conserved. The repeat sequences are postulated to act as target sites for intragenic recombination events that result in variable numbers of repeats within the different sfb genes. A model of the Sfb protein is presented.

Identification of a fibronectin-binding protein as adhesin of Streptococcus pyogenes

The role of streptococcal fibronectin-binding protein (Sfb protein) in the adherence of Streptococcus pyogenes to epithelial cells was analyzed by using a recombinant Sfb fusion protein which was constructed by fusion of the binding domain of Sfb protein to MS2 polymerase. Sfb fusion protein was overexpressed in Escherichia coli, purified from E. coli lysates by FPLC and analysed in binding experiments with 125I-labelled fibronectin and adherence studies with HEp2 epithelial cells. Lysates from E. coli expressing the fusion protein as well as purified Sfb protein competitively inhibited fibronectin binding and epithelial cell adherence of S. pyogenes, whereas streptococcal lipoteichoic acid (LTA), previously suggested to be the adhesin of S. pyogenes, had no effects. Southern blot analysis of chromosomal DNA from various streptococci revealed that the gene coding for the binding domain of Sfb protein was also present in other S. pyogenes strains. These results indicate that fibronectin-binding protein is the major adhesin of S. pyogenes.

Role of fibronectin in staphylococcal colonisation of fibrin thrombi and plastic surfaces

The adhesive glycoprotein fibronectin has been proposed as a mediator of adherence of certain gram-positive cocci to host cells and fibrin thrombi. This study compared the role of soluble and immobilised fibronectin in the adherence of coagulase-negative staphylococci (CNS) and Staphylococcus aureus to fibrin thrombi and plastic surfaces. Adherence of S. epidermidis to fibrin thrombi was significantly reduced when fibronectin was removed from the plasma used for thrombus preparation. Adherence was restored through restitution of fibronectin. S. epidermidis also adhered substantially more to plastic surface coated with fibronectin than to non-coated plastic. Increased adherence of CNS to plastic was also observed after coating with the 29-kDa N-terminal fragment of fibronectin. Soluble fibronectin did not affect the adherence of CNS to fibrin thrombi or plastic surfaces. The adherence of S. aureus to fibrin thrombi was significantly increased by the addition of soluble fibronectin, but not by incorporation of fibronectin into the clot. These results indicate that the binding of fibronectin is an important factor in the adherence of staphylococci to fibrin clots and plastic surfaces and, thus, colonisation of these surfaces. However, the two species of staphylococci seem to employ different mechanisms of fibronectin-mediated adherence: S. epidermidis interacts mainly with fibronectin incorporated in fibrin clots or immobilised on implanted synthetic materials, whereas S. aureus adheres to the fibrin matrix through binding of soluble fibronectin present in wound exudates.

Protein antigens secreted by Mycobacterium paratuberculosis

Proteins secreted by Mycobacterium paratuberculosis (M.ptb) during short-term cultivations were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western(Immuno) blotting. Cultivation in a defined medium containing 35S methionine allowed autoradiographic detection of proteins which had been secreted or passively released by actively metabolizing M.ptb organisms. After the first 3 days of cultivation, 4 proteins with molecular weights of approximately 38, 50, 65 and 110 kilodaltons (kd) were detected on SDS gels. Longer incubation up to 12 days resulted in an increased concentration of these proteins as well as in appearance of additional proteins ranging from 14 to over 90 kd. In long-term (8-10 weeks) culture filtrates only two prominent proteins with molecular weights of 30 and 65 kd proteins could be detected. Immunoblot analysis showed that some of the proteins secreted during short-term cultivations were recognized by sera from M.ptb-infected sheep and more significantly by sera from animals which had been immunized with a M.ptb live vaccine strain. The study indicates that during short incubation times M.ptb may secrete immunoreactive proteins which are not dominant in long-term cultures.

Fibronectin-binding protein of Streptococcus pyogenes: sequence of the binding domain involved in adherence of streptococci to epithelial cells

The sequence of the fibronectin-binding domain of the fibronectin-binding protein of Streptococcus pyogenes (Sfb protein) was determined, and its role in streptococcal adherence was investigated by use of an Sfb fusion protein in adherence studies. A 1-kb DNA fragment coding for the binding domain of Sfb protein was cloned into the expression vector pEX31 to produce an Sfb fusion protein consisting of the N-terminal part of MS2 polymerase and a C-terminal fragment of the streptococcal protein. Induction of the vector promoter resulted in hyperexpression of fibronectin-binding fusion protein in the cytoplasm of the recombinant Escherichia coli cells. Sequence determination of the cloned 1-kb fragment revealed an in-frame reading frame for a 268-amino-acid peptide composed of a 37-amino-acid sequence which is completely repeated three times and incompletely repeated a fourth time. Cloning of one repeat into pEX31 resulted in expression of small fusion peptides that show fibronectin-binding activity, indicating that one repeat contains at least one binding domain. Each repeat exhibits two charged domains and shows high homology with the 38-amino-acid D3 repeat of the fibronectin-binding protein of Staphylococcus aureus. Sequence comparison with other streptococcal ligand-binding surface proteins, including M protein, failed to reveal significant homology, which suggests that Sfb protein represents a novel type of functional protein in S. pyogenes. The Sfb fusion protein isolated from the cytoplasm of recombinant cells was purified by fast protein liquid chromatography. It showed a strong competitive inhibition of fibronectin binding to S. pyogenes and of the adherence of bacteria to cultured epithelial cells. In contrast, purified streptococcal lipoteichoic acid showed only a weak inhibition of fibronectin binding and streptococcal adherence. These results demonstrate that Sfb protein is directly involved in the fibronectin-mediated adherence of S. pyogenes to epithelial cells.

Mycobacterium paratuberculosis binds fibronectin

Fibronectin, an adhesive glycoprotein which is present in plasma and on many host cell surfaces of many host organisms, binds to certain bacterial pathogens. This study demonstrates the ability of Mycobacterium paratuberculosis (M.ptb) to interact with 125I-labelled fibronectin purified from bovine and ovine plasma. Two M.ptb strains were tested: a clinical isolate and a commercially available vaccine strain. Both strains showed significant fibronectin-binding activities of 22 and 41%, respectively, whereas non-pathogenic M.phlei had almost no affinity for fibronectin. Binding activities were similar for ovine and bovine fibronectin. We found that fibronectin binding by M.ptb was (1) time-dependent, reaching saturation within 90 min, (2) specific, since it was inhibited by an excess of unlabelled fibronectin but not by albumin, (3) saturable, with an apparent dissociation constant of 1.25 x 10(-9) M and a maximal number of 1,600 binding sites per bacterium, and (4) sensitive to detergents, proteases and heat treatments, indicating the protein nature of the responsible binding component(s). Scatchard plot analysis gave a straight line suggesting the presence of a single type of fibronectin receptor on M.ptb.

Inhibitory effects of fibrinogen on phagocytic killing of streptococcal isolates from humans, cattle and horses

The effects of fibrinogen on phagocytic killing of Streptococcus dysgalactiae from cattle and S. equi from horses were studied in comparison to that of S. pyogenes from humans. Phagocytic killing was determined by a fluorometric microassay using glass adherent polymorphonuclear neutrophils (PMN) from the respective host species, preopsonization with homologous sera led to a dose-dependent increase in phagocytic killing of all streptococcal cultures, preincubation of streptococci with fibrinogen significantly inhibited their phagocytic killing. Fibrinogen had no effect on phagocytic killing of non-fibrinogen binding S. agalactiae cultures. Further characterization studies with S. dysgalactiae and S. pyogenes revealed that a partial inhibition of phagocytic killing could also be achieved by preincubation with monomeric beta-chains of fibrinogen. Digestion of the fibrinogen binding sites on streptococci with proteases resulted in an almost complete loss of the inhibitory effects of fibrinogen on phagocytic killing. It could thus be concluded that by binding fibrinogen animal pathogenic streptococci could evade phagocytic killing in a similar manner as M protein carrying S. pyogenes isolates from human infections.

Antibody reactivities of Mycobacterium paratuberculosis infected sheep as analyzed by enzyme-linked immunosorbent assay and western blotting

Antibody reactivities in sera from Mycobacterium paratuberculosis (M. ptb) infected and vaccinated sheep were analyzed by enzyme-linked immunosorbent assay (ELISA) and Western (immuno)blotting using a sonicate antigen from M. ptb. Both methods allowed good differentiation between infected/vaccinated animals and noninfected controls. Removal of nonspecific crossreactive antibodies by absorption with a M. phlei sonicate antigen coupled to Sepharose reduced ELISA reactivities of positive sera by 50% and those of noninfected serum by 85%. Immunoblotting analysis revealed that reduction by M. phlei absorption was due to lower reactivities of M. ptb antigens in the range of 30 to 45 kDa. However, one protein with a molecular mass of approx. 27 kDa seemed to be specific for M. ptb since it reacted similarly with nonabsorbed and absorbed serum but not with antibodies which were eluted from M. phlei-Sepharose after absorption. Our findings indicate that M. ptb and M. phlei share a number of common antigens of potential pathogenic importance and that only a smaller part of proteins (i.e. the 27 kDa protein) might be specific for M. ptb.

Bacterial infection of wounds: fibronectin-mediated adherence group A and C streptococci to fibrin thrombi in vitro

Adherence of group A, B, and C streptococci to fibrin thrombi was studied by using a novel fluorochrome microassay carried out in microdilution plates in which fibrin thrombi had been prepared by clotting citrated human, cattle, or horse plasma. Substantial adherence was observed with various strains of group A and C streptococci, whereas little was observed with group B streptococci. Adherence of all group A and C streptococcal strains decreased by up to 40% when fibronectin was depleted from the plasmas used for preparing fibrin thrombi, and fibronectin repletion increased adherence of streptococci in a dose-dependent manner. Addition of the 210-kilodalton C-terminal fragment of fibronectin to fibronectin-depleted plasma restored the adherence of group C but not group A streptococci, whereas addition of the 29-kilodalton N-terminal fragment was without any effect for all tested streptococcal strains. Prior incubation of group A and C streptococcal strains with fibronectin markedly increased their adherence, but treatment with proteases abolished their ability to adhere to fibrin thrombi. Adherence of group B streptococci was not affected by either fibronectin depletion or proteolytic digestion. These results indicate that both fibronectin incorporated into the fibrin matrix of thrombi and soluble fibronectin can mediate adherence of group A and C streptococci to fibrin thrombi and that binding sites for fibronectin located on the bacterial surface mediate this adherence.

Role of alpha 2-macroglobulin in phagocytosis of group A and C streptococci

Binding of alpha 2-macroglobulin (alpha 2M) to streptococci and its effects on phagocytosis were investigated. Two types of streptococcal binding sites for alpha 2M were observed: Streptococcus pyogenes from human infections interacted only with native alpha 2M whereas S. dysgalactiae from bovine and S. equi from equine infections bound only a complex of alpha 2M with trypsin (alpha 2M-T). Preincubation of S. pyogenes with native alpha 2M substantially enhanced their phagocytosis by human polymorphonuclear neutrophils (PMN) whereas preincubation with alpha 2M-T was without any effect. On the other hand, incubation of S. dysgalactiae and S. equi with alpha 2M-T markedly reduced their phagocytosis by PMN from the respective host species. Native alpha 2M did not affect the phagocytosis of these streptococci. Digestion of the streptococcal binding sites for alpha 2M and alpha 2M-T pronase abolished the enhancement of phagocytosis of S. pyogenes by native alpha 2M as well as the inhibition of phagocytosis of S. dysgalactiae and S. equi by alpha 2M-T. Thus, binding of alpha 2M or its complexes appeared to play a role in streptococcal pathogenicity.

Role of complement S protein (vitronectin) in adherence of Streptococcus dysgalactiae to bovine epithelial cells

The binding of bovine complement S protein (vitronectin) to Streptococcus dysgalactiae isolates from cattle with mastitis and the S protein's role in streptococcal adherence to bovine epithelial cells were investigated. All 25 clinical isolates of S dysgalactiae interacted with bovine S protein. None of the other streptococcal species tested bound to bovine S protein. The S protein-binding sites were saturable and highly sensitive to trypsin. The binding of bovine S protein to S dysgalactiae isolates was specific and could not be inhibited by other plasma proteins, such as fibronectin, albumin, fibrinogen, alpha 2-macroglobulin, or IgG. Similarly, streptococcal binding of bovine S protein was not influenced by the synthetic peptide Gly-Arg-Gly-Asp-Ser, which constituted the host cell attachment sequence of S protein. In adherence experiments, prior binding of bovine S protein to S dysgalactiae enhanced streptococcal adherence to bovine epithelial cells. The enhancing effects by bovine S protein were abolished when the respective binding sites on the streptococci were digested by trypsin. Thus, bovine S protein could be an important mediator of adherence of S dysgalactiae to bovine epithelial cells.

Mediation of adherence of streptococci to human endothelial cells by complement S protein (vitronectin)

The role of S protein in the adherence of group A and G streptococci to human umbilical vein endothelial cells cultivated in 96-well microdilution plates was studied by utilizing fluorescein-labeled streptococci. The assay proved suitable for quantitative determination of bacterial adherence to cultured endothelial cells for all tested strains of streptococci. Only bacterial strains with significant S protein binding but weak fibronectin binding were included in these studies. Fibronectin-mediated adherence to endothelial cells of these streptococci was less than 25% of total and could be blocked by antifibronectin immunoglobulin G. Further treatment of endothelial cell monolayers with anti-S protein immunoglobulin G at concentrations up to 1 mg per well led to an almost complete inhibition of adherence for all tested streptococcal cultures, indicating significant contribution of S protein in the streptococcus-endothelial cell interaction. Blocking of S-protein-binding sites on streptococci by preincubation with exogeneous S protein at a concentration of 10 micrograms per 4 x 10(7) streptococci led to about 75% reduction of S-protein-mediated adherence to endothelial cells. Trypsin pretreatment of group G streptococci and pronase pretreatment of group A and G streptococci, modifications known to destroy the bacterial binding sites of S protein, also inhibited the capacity of the streptococci for S-protein-mediated adherence to endothelial cells by 75 to 80%. These results indicate that S protein plays a mediatory role in adherence of streptococci to endothelial cells and that S-protein-specific binding sites on streptococci are involved in this interaction.

Adherence of streptococcal isolates from cattle and horses to their respective host epithelial cells

Adherence of Streptococcus dysgalactiae isolates from cattle and S equi isolates from horses to their respective host epithelial cells was compared with the adherence of S pyogenes to human epithelial cells. The adherence was quantitatively determined by use of fluorescein-labeled streptococci. All 3 streptococcal species adhered selectively to their respective host cells. The mechanism of adherence was evaluated by binding studies with adhesive plasma protein, fibronectin. Although all 3 streptococcal species bound fibronectin, S dysgalactiae and S equi interacted preferentially with a 210-kilodalton (kD) C-terminal fragment of fibronectin, whereas S pyogenes bound only a 29-kD N-terminal fragment. A synthetic peptide Gly-Arg-Gly-Asp-Ser, representing the host cell attachment site of fibronectin, partially inhibited the binding of fibronectin and of its 210 kD fragment to S dysgalactiae, but not to S equi. The binding of fibronectin and its 29-kD fragment to S pyogenes was not inhibited by Gly-Arg-Gly-Asp-Ser. These differences in binding activities corresponded to the ability of fibronectin to mediate the adherence of the streptococci to the epithelial cells: fibronectin strongly inhibited the adherence of S pyogenes and S equi to the epithelial cells, but only weakly inhibited that of S dysgalactiae.

A simple method for quantitative determination of bacterial adherence to human and animal epithelial cells

A simple quantitative method for determining bacterial adherence to epithelial cells was devised. The method involved incubation of fluorescein-labeled bacteria with oral epithelial cells. Non-adherent bacteria were subsequently removed by Percoll density centrifugation. The degree of bacterial adherence was then determined fluorospectrophotometrically by measuring the fluorescein extracted from the adherent bacteria. The degree of adherence corresponded well with the microscopic counts of adherent bacteria. The method proved to be suitable for assaying adherence of both gram-positive and gram-negative bacteria to human as well as animal epithelial cells.