- Research article
- Open Access
The cell envelope subtilisin-like proteinase is a virulence determinant for Streptococcus suis
© Bonifait et al; licensee BioMed Central Ltd. 2010
Received: 18 September 2009
Accepted: 10 February 2010
Published: 10 February 2010
Streptococcus suis is a major swine pathogen and zoonotic agent that mainly causes septicemia, meningitis, and endocarditis. It has recently been suggested that proteinases produced by S. suis (serotype 2) are potential virulence determinants. In the present study, we screened a S. suis mutant library created by the insertion of Tn917 transposon in order to isolate a mutant deficient in a cell surface proteinase. We characterized the gene and assessed the proteinase for its potential as a virulence factor.
Two mutants (G6G and M3G) possessing a single Tn917 insertion were isolated. The affected gene coded for a protein (SSU0757) that shared a high degree of identity with Streptococccus thermophilus PrtS (95.9%) and, to a lesser extent, with Streptococcus agalactiae CspA (49.5%), which are cell surface serine proteinases. The SSU0757 protein had a calculated molecular mass of 169.6 kDa and contained the catalytic triad characteristic of subtilisin family proteinases: motif I (Asp200), motif II (His239), and motif III (Ser568). SSU0757 also had the Gram-positive cell wall anchoring motif (Leu-Pro-X-Thr-Gly) at the carboxy-terminus, which was followed by a hydrophobic domain. All the S. suis isolates tested, which belonged to different serotypes, possessed the gene encoding the SSU0757 protein. The two mutants devoid of subtilisin-like proteinase activity had longer generation times and were more susceptible to killing by whole blood than the wild-type parent strain P1/7. The virulence of the G6G and M3G mutants was compared to the wild-type strain in the CD1 mouse model. Significant differences in mortality rates were noted between the P1/7 group and the M3G and G6G groups (p < 0.001).
In summary, we identified a gene coding for a cell surface subtilisin-like serine proteinase that is widely distributed in S. suis. Evidences were brought for the involvement of this proteinase in S. suis virulence.
The swine pathogen Streptococcus suis is transmitted via the respiratory route and colonizes the palatine tonsils and nasal cavities of pigs from where it can disseminate throughout the animal and cause infections , mainly septicemia, meningitis, and endocarditis, as well as arthritis . Zoonotic infections occur mainly in individuals who work in close contact with pigs or pork by-products . In fact, S. suis is considered one of the most important etiologic agents of adult meningitis in Asian countries . While thirty-five serotypes (1 to 34 and 1/2) have been identified based on capsular antigens, serotype 2 is considered the most virulent and is the most commonly recovered from diseased pigs and humans . Over the past ten years, numerous studies have been undertaken to identify putative virulence factors in S. suis [1, 4, 5]. Among these virulence factors, the polysaccharide capsule, which provides protection against phagocytosis , appears to be essential for the pathogenicity of S. suis. However, considering the multi-step pathogenesis of S. suis infections, it is likely that the virulence of this pathogen is determined by more than one factor .
Proteases, which are hydrolytic enzymes that catalyze the cleavage of peptide bonds, are critical virulence factors for numerous microbial pathogens . These enzymes hydrolyze a variety of host proteins, including serum and tissue components, thus helping to neutralize the host immune defense system and causing tissue destruction and invasion . Interestingly, these enzymes show great potential as vaccine antigens and are promising targets for the development of anti-bacterial drugs . A previous study in our laboratory identified four proteolytic enzymes produced by S. suis, including one on the cell surface that degrades a chromogenic substrate highly specific for chymotrypsin-like proteases . In the present study, we screened an S. suis P1/7 (serotype 2) mutant library created by the insertion of Tn917 transposon in order to isolate a mutant deficient in this activity. We characterized the gene and assessed the proteinase for its potential as a virulence factor.
Bacteria and mutant library
S. suis P1/7, a virulent serotype 2 European reference strain isolated from a pig with meningitis for which the genome has been sequenced by the S. suis Sequencing Group at the Sanger Institute , was used as the wild-type strain. Bacteria were routinely grown in Todd Hewitt broth (THB; BBL Microbiology Systems, Cockeysville, MA, USA) at 37°C under aerobiosis. A mutant library was constructed in a previous study  using the pTV408 temperature-sensitive suicide vector to deliver the Tn917 transposon into S. suis P1/7 via electroporation. To maintain the selective pressure during the growth of the mutants, the culture medium was supplemented with 1 μg/ml of erythromycin. Escherichia coli MC1061 (hsdR2 hsdM+ hsdS+ araD139 Δ(ara-leu)7697 Δ(lac)X74 galE15 galK16 rpsL (StrR) mcrA mcrB1), which was used for plasmid rescue, was grown in LB medium containing 100 μg/ml of erythromycin.
Isolation of mutants deficient in proteinase activity
Mutants from the Tn917 library were individually grown overnight in THB and suspended in phosphate-buffered saline (PBS, 50 mM, pH 7.2) to an optical density of 1.0 at 660 nm (OD660). Bacterial suspensions (100 μl) were added to the wells of 96-well microplates along with 20 μl of the chromogenic substrate N-succinyl-Ala-Ala-Pro-Phe-p Na (2 mg/ml in 50% dimethyl formamide) (Sigma-Aldrich Canada Ltd., Oakville, ON, CANADA). This substrate is highly specific for subtilisin-like  and chymotrypsin-like enzymes . The reaction mixtures were incubated at 37°C for 4 h. The release of p NA was quantified by measuring the absorbance at 415 nm (A415).
Demonstration of transposon insertion and stability of mutants
Chromosomal DNA was isolated from cells harvested from overnight bacterial cultures as previously reported , except that proteinase K (Sigma-Aldrich Canada Ltd.) was used instead of protease I. The DNA was digested with Hind III restriction endonuclease, Southern blotted, and hybridized using a digoxigenin (DIG)-labeled probe specific for the erm gene in the Tn917 transposon as previously reported . Hybridization was performed at 68°C, and the probe was detected using the NBT (p-nitroblue tetrazolium chloride)/BCIP (5-bromo-4-chloro-3-indolyl phosphate) chromogen system. The probe was generated from pTRKL2T  by PCR using the ermF 5'-ACGAGTGAAAAAGTACTCAACC-3' and ermR 5'-ACCTCTGTTTGTTAGGGAATTG-3' primers and the DIG-PCR labeling mixture. The stability of the Tn917-induced mutation was investigated by performing overnight serial passages (up to 35) of the mutants in erythromycin-free THB prior to measuring the hydrolysis of the chromogenic substrate N-succinyl-Ala-Ala-Pro-Phe-p Na as described above.
Plasmid rescue and sequencing of the insertion site
The site of the transposon insertions in the S. suis P1/7 genome was determined by plasmid rescue . The genomic DNA of the selected mutants was isolated and digested using Hind III, ligated, and transformed into chemically competent E. coli MC1061. Transformants were selected on LB agar containing erythromycin. Plasmid DNA was then extracted from the E. coli cells and was sequenced using the Tn917 (5'-aGAGAGATGTCACCGTCAAGT-3') primer to determine the DNA sequence contiguous to Tn917.
Characterization and comparative analysis of SSU0757
The theoretical pI and molecular mass of SSU0757 were determined using software available at http://www.scripps.edu/~cdputnam/protcalc.html. The alignment and comparison of the amino acid sequences of the subtilisin-like serine proteinases was performed using BioEdit software.
Distribution of SSU0757 in S. suis
Selected S. suis strains were tested for the presence of the subtilisin-encoding gene (SSU0757): S428 (serotype 1), 31533 (serotype 2), 89-999 (serotype 2), S735 (serotype 2), 90-1330 (serotype 2), 65 (serotype 2), 89-4223 (serotype 2), 2651 (serotype 1/2), 4961 (serotype 3), Amy12C (serotype 5), 1078212 (untypeable), and 1079277 (untypeable). Except for strains 90-1330, 65 and 89-4223, which were isolated from healthy pigs, all other isolates were from diseased pigs. Cell lysates were prepared from bacterial colonies recovered from agar plates. The presence of the gene was determined by PCR using the SUB163 (5'-GTCAGCGAATCAGCCTCAGAAAGTCCCGTT-3') and SUB4436R (5'-CTTCATCTTTTTTGTCAGTGGCAGTATTTG-3') primers.
The generation times of S. suis wild-type strain P1/7 and the proteinase-deficient mutants were determined by inoculating erythromycin-free THB with late-log phase cultures and monitoring growth at OD660. Generation times were calculated from the growth curves.
Susceptibility to whole blood
Venous blood samples were collected from the antecubital vein of a human volunteer using the Vacutainer™ system and sterile endotoxin-free blood collection tubes containing 150 IU of sodium heparin (Becton Dickinson, Franklin Lakes, NJ, USA). Informed consent was obtained from the donor prior to the experiment. The protocol was approved by the Université Laval ethics committee. S. suis (wild-type parent strain and mutants) were cultivated to the early stationary growth phase at 37°C. The cells were harvested by centrifugation at 11,000 g for 10 min, suspended in RPMI-1640 medium to an OD660 of 0.1, and diluted 1:100 in RPMI-1640 medium. Whole blood (1 ml) was mixed with pig serum anti-S. suis (300 μl) and S. suis cells (100 μl). Anti-S. suis serum was prepared in pigs by injecting whole bacterial cells as previously described . The mixtures were incubated for 4 h at 37°C with occasional gentle shaking. Infected whole blood cultures were harvested at 0 and 4 h. The first time point (0 h) was considered as the 100% viability control. Infected whole blood samples were 10-fold serially diluted (10-1 to 10-4) in PBS and plated on Todd-Hewitt agar plates. After a 24-h incubation at 37°C, the number of colony forming units (cfu) was determined. The experiments were carried out in duplicate.
Experimental infections in mice
Thirty-nine female six-week-old CD1 mice (Charles River Laboratories, Saint-Constant, QC, Canada) were acclimatized to a 12 h light/dark cycle and were given rodent chow and water ad libitum. On the day of the experiment, the mice (11 per group) were infected by i.p. injection of 1 ml of either S. suis wild-type strain P1/7 or the Tn917 mutants deficient in proteinase activity at a concentration of 7 × 107 CFU/ml in THB. Six control mice were inoculated with the vehicle solution (sterile THB) alone. The CD1 mouse has proven to be an excellent model of S. suis infections that result in an early septic shock-like syndrome and a second late phase S. suis infection that induces meningitis and brain damage [18–20]. The septicemic phase of S. suis infections is characterized by depression, rough hair coat, swollen eyes, weakness, and death during the first 48 h post-infection. If animals survive this critical step of the disease, they may still develop central nervous system damage and meningitis, with the sudden appearance of nervous signs beginning 3-4 days post-infection, including hyperexcitation, episthotonus, opisthotonus, bending of the head toward one side, and walking in circles . Clinical signs of infection and survival were recorded on a daily basis post-infection for 14 days as previously described . Mice exhibiting extreme lethargy or neurological signs were considered moribund and were humanely euthanized. All experiments involving mice were conducted in accordance with the guidelines and policies of the Canadian Council on Animal Care and the principles set out in the Guide for the Care and Use of Laboratory Animals, and were approved by the Animal Welfare Committee of Université de Montréal. Overall survival rates for the various groups were calculated using Kaplan-Meier plots. Survival curves were compared using the log-rank test with the Holm-Sidak method used to analyze multiple curves. A p < 0.05 was considered statistically significant. All analyses were performed using the Sigma Plot System (v.11; Systat Software, San Jose, CA, USA).
An in silico analysis of the SSU0757 gene product was performed to determine principal characteristics of the protein. This revealed that it corresponds to a 1,585-residue polypeptide with a predicted pI of 4.58 and a calculated molecular mass of 169.6 kDa. The protein contained the catalytic triad characteristic of subtilisin family proteinases: motif I (Asp200), motif II (His239), and motif III (Ser568). It also contained the Gram-positive cell wall anchoring motif (Leu-Pro-X-Thr-Gly) at the carboxy-terminus at positions 1551-1555 followed by a hydrophobic domain as well as an amino-terminal signal sequence with a putative cleavage site between residues 35 and 36 (Figure 2).
Percentage identity of the amino acid (a.a.) sequences of S. suis P1/7 SSU0757 with proteinases from other streptococcal species.
Predicted a.a. sequence % identity
S. suis uncharacterized protein
A4VUI8 + A4VUI9
S. suis uncharacterized protein
A4WOT0 + A4WOT1
S. thermophilus PrtS
S. agalactiae CspA
S. sanguinis PrtS
S. pyogenes PrtS
S. pyogenes ScpC
S. pyogenes ScpA
S. agalactiae ScpB
S. pneumoniae PrtA
Generation times of S. suis P1/7 and the Tn917 mutants deficient in the cell surface subtilisin-like proteinase.
Generation time in minutes
(mean ± standard deviation)
45.3 ± 6.9
57.6 ± 8.2
55.8 ± 4.8
Virulence in CD1 mice of S. suis wild-type strain P1/7 and mutants M3G and G6G.
Bacterial pathogens possess various surface proteins, most of which are virulence determinants involved in attachment, multiplication, and invasion of the host. In the present study, we identified a S. suis gene that codes for a cell surface subtilisin-like proteinase containing the cell wall sorting signal LPXTG that is responsible for covalently anchoring proteins to cell wall peptidoglycan. The sortase A previously identified in S. suis has been reported to play an important role in anchoring LPXTG proteins to the cell wall  and may be involved in locating the subtilisin-like proteinase on the cell surface. A number of potential virulence factors previously characterized in S. suis, including the opacity factor , the virulence marker MRP , the surface antigen one , and a surface protein associated with invasion of porcine brain endothelial cells , contain the anchoring motif LPXTG,.
The cell surface subtilisin-like proteinase of S. suis showed the highest identity with the PrtS of S. thermophilus (95.9%) and the CspA of S. agalactiae (49.5%). In the dairy lactic bacterium S. thermophilus, the PrtS subtilisin-like proteinase degrades casein into peptides, which are required for efficient growth [27, 28]. S. agalactiae is a major causal agent of mastitis in cattle  and is the principal cause of neonatal meningitis . The CspA subtilisin-like proteinase of this pathogenic streptococcus is considered to be a critical virulence factor . This proteinase has been shown to be involved in bacterial virulence in a neonatal rat sepsis model and in resistance to opsonophagocytic killing by human neutrophils in vitro . More recently, the CspA of S. agalactiae has been shown to hydrolyze and inactivate CXC chemokines, many of which can recruit neutrophils to sites of infection .
Bacterial pathogenicity is a complex process that depends on the ability of the pathogen to multiply. The S. suis subtilisin-like proteinase appears to contribute to nutrient acquisition given that proteinase-deficient mutants had longer generation times than the parent strain in vitro. This is consistent with the study of Courtin et al. , who reported that the PrtS subtilisin-like proteinase of S. thermophilus is involved in nitrogen supply through casein hydrolysis. The mutants and the wild type strain were also compared for their ability to survive in human whole blood. We found that the parent strain was much more resistant to killing than the mutants. This suggests that the proteinase may degrade human serum proteins with bactericidal activity or opsonins involved in phagocytosis by immune cells. This is in agreement with the study of Harris et al. , who reported that the CspA subtilisin-like proteinase of S. agalactiae, which shares a high degree of identity with S. suis, contributes to the resistance to phagocytosis by neutrophils.
Given its cell surface localization, the subtilisin-like proteinase of S. suis may interact with host cells and induce an inflammatory response which is a feature of meningitis. Indeed, the S. suis proteinase may activate protease-activated receptors (PAR), which are members of the G protein-coupled receptors also known as seven-transmembrane domain receptors . These receptors are found on several cell types and play an important role in inflammatory processes. More specifically, PAR-2 is known to be activated by serine proteases and bacterial proteinases . Since S. suis cells are known to induce the production of pro-inflammatory cytokines by endothelial cells  and macrophages , part of this activation may be caused by the cell surface subtilisin-like proteinase identified in this study. Studies are currently in progress in our laboratory to verify this hypothesis. In a previous study, we reported that the presence of fibrinogen during growth of S. suis modulates its capacity to form a biofilm . Given the ability of bacterial subtilisin-like proteinases to degrade fibrinogen [22, 37, 38], it may be hypothesized that the proteinase of S. suis could cleave fibrinogen leading to generation of fibrin, which may favor biofilm formation.
The contribution of the subtilisin-like proteinase to virulence was investigated in a mouse model. We found that the proteinase-deficient Tn917 mutants were significantly less virulent in mice. This clearly suggests that the S. suis subtilisin-like proteinase is an virulence determinant. Ge et al.  recently constructed a dipeptidyl peptidase IV deficient-mutant of S. suis and provided evidence for the critical role of this enzyme in the virulence of S. suis in a mouse model. This cell surface enzyme cleaves X-Pro/Ala dipeptides from the N-terminus of proteins but also possesses binding domains for fibronectin . Given the involvement of the cell surface subtilisin-like serine proteinase in S. suis virulence, studies are in progress to clone this proteinase and determine whether it may represent a promising candidate for a protein-based vaccine.
In summary, we identified a gene that codes for a cell surface subtilisin-like serine proteinase and that is widely distributed in S. suis strains. Evidences were brought for the involvement of this proteinase in S. suis virulence.
This study was supported by a grant from the Natural Sciences and Engineering Research Council of Canada (NSERC). We thank S. Lacouture, M.-P. Levasseur, and A. Turgeon for their technical assistance.
- Higgins R, Gottschalk M: Streptococcal Diseases. Diseases of Swine. Edited by: Straw BE, D'Allaire S, Mengeling WL, Taylor DJ. 2005, Iowa: Iowa University Press, 769-783. 9Google Scholar
- Lun ZR, Wang QP, Chen XG, Li AX, Zhu XQ: Streptococcus suis: an emerging zoonotic pathogen. Lancet Infect Dis. 2007, 7: 201-209. 10.1016/S1473-3099(07)70001-4.View ArticlePubMedGoogle Scholar
- Wertheim HF, Nghia HD, Taylor W, Schultsz C: Streptococcus suis: an emerging human pathogen. Clin Infect Dis. 2009, 48: 617-625. 10.1086/596763.View ArticlePubMedGoogle Scholar
- Gottschalk M, Segura M: The pathogenesis of the meningitis caused by Streptococcus suis: the unresolved questions. Vet Microbiol. 2000, 76: 259-272. 10.1016/S0378-1135(00)00250-9.View ArticlePubMedGoogle Scholar
- Segura M, Gottschalk M: Extracellular virulence factors of streptococci associated with animal diseases. Front Biosci. 2004, 9: 1157-1188. 10.2741/1287.View ArticlePubMedGoogle Scholar
- Charland N, Harel J, Kobisch M, Lacasse S, Gottschalk M: Streptococcus suis serotype 2 mutants deficient in capsular expression. Microbiology. 1998, 144: 325-332. 10.1099/00221287-144-2-325.View ArticlePubMedGoogle Scholar
- Baums CG, Valentin-Weigand P: Surface-associated and secreted factors of Streptococcus suis in epidemiology, pathogenesis and vaccine development. Anim Health Res Rev. 2009, 10: 65-83. 10.1017/S146625230999003X.View ArticlePubMedGoogle Scholar
- Maeda H: Role of microbial proteases in pathogenesis. Microbiol Immunol. 1996, 40: 685-699.View ArticlePubMedGoogle Scholar
- Travis J, Potempa J: Bacterial proteinases as targets for the development of second-generation antibiotics. Biochim Biophys Acta. 2000, 1477: 35-50.View ArticlePubMedGoogle Scholar
- Jobin MC, Grenier D: Identification and characterization of four proteases produced by Streptococcus suis. FEMS Microbiol Lett. 2003, 220: 113-119. 10.1016/S0378-1097(03)00088-0.View ArticlePubMedGoogle Scholar
- Holden MT, Hauser H, Sanders M: Rapid evolution of virulence and drug resistance in the emerging zoonotic pathogen Streptococcus suis. PloS One. 2009, 4: e6072-10.1371/journal.pone.0006072.PubMed CentralView ArticlePubMedGoogle Scholar
- Slater JD, Allen AG, May JP, Bolitho S, Lindsay H, Maskell DJ: Mutagenesis of Streptococcus equi and Streptococcus suis by transposon Tn917. Vet Microbiol. 2003, 93: 197-206. 10.1016/S0378-1135(03)00030-0.View ArticlePubMedGoogle Scholar
- Davis BG, Shang X, DeSantis G, Bott RR, Jones JB: The controlled introduction of multiple negative charge at single amino acid sites in subtilisin Bacillus lentus. Bioorg Med Chem. 1999, 7: 2293-2301. 10.1016/S0968-0896(99)00167-4.View ArticlePubMedGoogle Scholar
- DelMar EG, Largman C, Brodrick JW, Geokas MC: A sensitive new substrate for chymotrypsin. Anal Biochem. 1979, 99: 316-320. 10.1016/S0003-2697(79)80013-5.View ArticlePubMedGoogle Scholar
- Stuart JG, Zimmerer EJ, Maddux RL: Conjugation of antibiotic resistance in Streptococcus suis. Vet Microbiol. 1992, 30: 213-222. 10.1016/0378-1135(92)90115-A.View ArticlePubMedGoogle Scholar
- Vaillancourt K, LeMay JD, Lamoureux M, Frenette M, Moineau S, Vadeboncoeur C: Characterization of a galactokinase-positive recombinant strain of Streptococcus thermophilus. Appl Environ Microbiol. 2004, 70: 4596-4603. 10.1128/AEM.70.8.4596-4603.2004.PubMed CentralView ArticlePubMedGoogle Scholar
- Chabot-Roy G, Willson P, Segura M, Lacouture S, Gottschalk M: Phagocytosis and killing of Streptococcus suis by porcine neutrophils. Microb Pathog. 2006, 41: 21-32. 10.1016/j.micpath.2006.04.001.View ArticlePubMedGoogle Scholar
- Domínguez-Punaro MC, Segura M, Plante M, Lacouture S, Rivest S, Gottschalk M: Streptococcus suis serotype 2, an important swine and human pathogen, induces strong systemic and cerebral inflammatory responses in a mouse model of infection. J Immunol. 2007, 179: 1842-1854.View ArticlePubMedGoogle Scholar
- Fittipaldi N, Sekizaki T, Takamatsu D, Domínguez-Punaro MC, Harel J, Bui NK, Vollmer W, Gottschalk M: Significant contribution of the pgdA gene to the virulence of Streptococcus suis. Mol Microbiol. 2008, 70: 1120-1135. 10.1111/j.1365-2958.2008.06463.x.View ArticlePubMedGoogle Scholar
- Vanier G, Slater JD, Domínguez-Punaro MC, Fittipaldi N, Rycroft AN, Segura M, Maskell DJ, Gottschalk M: New putative virulence factors of Streptococcus suis involved in invasion of porcine brain microvascular endothelial cells. Microbial Pathog. 2009, 46: 13-20. 10.1016/j.micpath.2008.10.003.View ArticleGoogle Scholar
- Okwumabua O, Persaud JS, Reddy PG: Cloning and characterization of the gene encoding the glutamate dehydrogenase of Streptococcus suis serotype 2. Clin Diagn Lab Immunol. 2001, 8: 251-257.PubMed CentralPubMedGoogle Scholar
- Harris TO, Shelver DW, Bohnsack JF, Rubens CE: A novel streptococcal surface protease promotes virulence, resistance to opsonophagocytosis, and cleavage of human fibrinogen. J Clin Invest. 2003, 111: 61-70.PubMed CentralView ArticlePubMedGoogle Scholar
- Osaki M, Takamatsu D, Shimoji Y, Sekizaki T: Characterization of Streptococcus suis genes encoding proteins homologous to sortase of gram-positive bacteria. J Bacteriol. 2002, 184: 971-982. 10.1128/jb.184.4.971-982.2002.PubMed CentralView ArticlePubMedGoogle Scholar
- Baums CG, Kaim U, Fulde M, Ramachandran G, Goethe R, Valentin-Weigand P: Identification of a novel virulence determinant with serum opacification activity in Streptococcus suis. Infect Immun. 2006, 74: 6154-6162. 10.1128/IAI.00359-06.PubMed CentralView ArticlePubMedGoogle Scholar
- Vecht U, Arends JP, Molen Van der EJ, van Leengoed LA: Differences in virulence between two strains of Streptococcus suis type II after experimentally induced infection of newborn germ-free pigs. Am J Vet Res. 1989, 50: 1037-1043.PubMedGoogle Scholar
- Li Y, Martinez G, Gottschalk M, Lacouture S, Willson P, Dubreuil JD, Jacques M, Harel J: Identification of a surface protein of Streptococcus suis and evaluation of its immunogenic and protective capacity in pigs. Infect Immun. 2006, 74: 305-312. 10.1128/IAI.74.1.305-312.2006.PubMed CentralView ArticlePubMedGoogle Scholar
- Fernandez-Espla MD, Garault P, Monnet V, Rul F: Streptococcus thermophilus cell wall-anchored proteinase: release, purification, and biochemical and genetic characterization. Appl Environ Microbiol. 2000, 66: 4772-4778. 10.1128/AEM.66.11.4772-4778.2000.PubMed CentralView ArticlePubMedGoogle Scholar
- Courtin P, Monnet V, Rul F: Cell-wall proteinases PrtS and PrtB have a different role in Streptococcus thermophilus/Lactobacillus bulgaricus mixed culture in milk. Microbiology. 2002, 148: 3413-3421.View ArticlePubMedGoogle Scholar
- Keefe GP: Streptococcus agalactiae mastitis: a review. Can Vet J. 1997, 38: 429-437.PubMed CentralPubMedGoogle Scholar
- Larsen JW, Sever JL: Group B Streptococcus and pregnancy: a review. Am J Obstet Gynecol. 2008, 198: 440-448. 10.1016/j.ajog.2007.11.030.View ArticlePubMedGoogle Scholar
- Bryan JD, Shelver DW: Streptococcus agalactiae CspA is a serine protease that inactivates chemokines. J Bacteriol. 2009, 191: 1847-1854. 10.1128/JB.01124-08.PubMed CentralView ArticlePubMedGoogle Scholar
- Ossovskaya VS, Bunnett NW: Protease-activated receptors: contribution to physiology and disease. Physiol Rev. 2004, 84: 579-621. 10.1152/physrev.00028.2003.View ArticlePubMedGoogle Scholar
- Holzhausen M, Spolidorio LC, Vergnolle N: Role of protease-activated receptor-2 in inflammation, and its possible implications as a putative mediator of periodontitis. Mem Inst Oswaldo Cruz. 2005, 100 (Suppl 1): 177-180.View ArticlePubMedGoogle Scholar
- Vadeboncoeur N, Segura M, Al-Numani D, Vanier G, Gottschalk M: Pro-inflammatory cytokine and chemokine release by human brain microvascular endothelial cells stimulated by Streptococcus suis serotype 2. FEMS Immunol Med Microbiol. 2003, 35: 49-58. 10.1111/j.1574-695X.2003.tb00648.x.View ArticlePubMedGoogle Scholar
- Tanabe SI, Grenier D: Endothelial cell/macrophage cocultures as a model to study Strteptococcus suis -induced inflammatory responses. FEMS Immunol Med Microbiol. 2009, 55: 100-106. 10.1111/j.1574-695X.2008.00507.x.View ArticlePubMedGoogle Scholar
- Bonifait L, Grignon L, Grenier D: Fibrinogen induces biofilm formation by Streptococcus suis and enhances its antibiotic resistance. Appl Environ Microbiol. 2008, 74: 4969-4972. 10.1128/AEM.00558-08.PubMed CentralView ArticlePubMedGoogle Scholar
- Bamford CV, Fenno JC, Jenkinson HF, Dymock D: The chymotrypsin-like protease complex of Treponema denticola ATCC 35405 mediates fibrinogen adherence and degradation. Infect Immun. 2007, 75: 4364-4372. 10.1128/IAI.00258-07.PubMed CentralView ArticlePubMedGoogle Scholar
- Karlsson C, Andersson ML, Collin M, Schmidtchen A, Bjorck L, Frick IM: SufA--a novel subtilisin-like serine proteinase of Finegoldia magna. Microbiology. 2007, 153: 4208-4218. 10.1099/mic.0.2007/010322-0.View ArticlePubMedGoogle Scholar
- Ge J, Feng Y, Ji Hongfeng, Zhang H, Zheng F, Wang C, Yin Z, Pan X, Tang J: Inactivation of dipeptidyl peptidase IV attenuates the virulence of Streptococcus suis serotype 2 that cause streptococcal toxic shock syndrome. Curr Microbiol. 2009, 59: 248-255. 10.1007/s00284-009-9425-8.View ArticlePubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.