Patent Application: US-201314015881-A

Abstract:
the invention relates to streptococcus suis infection in pigs , vaccines directed against those infections and tests for diagnosing streptococcus suis infections . the invention provides an isolated or recombinant nucleic acid encoding a capsular gene cluster of streptococcus suis or a gene or gene fragment derivated thereof . the invention further provides a nucleic acid probe or primer allowing species or serotype - specific detection of streptococcus suis . the invention also provides a streptococcus suis antigen and vaccine derived thereof .

Description:
the bacterial strains and plasmids used in this study are listed in table 1 . s . suis strains were grown in todd - hewitt broth ( code cm189 , oxoid ), and plated on columbia agar blood base ( code cm331 , oxoid ) containing 6 % ( v / v ) horse blood . e . coli strains were grown in luria broth ( 28 ) and plated on luria broth containing 1 . 5 % ( w / v ) agar . if required , antibiotics were added to the plates at the following concentrations : spectinomycin : 100 μg / ml for s . suis and 50 μg / ml for e . coli and ampicillin , 50 μg / ml . serotyping . the s . suis strains were serotyped by the slide agglutination test with serotype - specific antibodies ( 44 ). dna techniques . routine dna manipulations were performed as described by sambrook et al . ( 36 ). alkaline phosphatase activity . to screen for phoa fusions in e . coli , plasmid libraries were constructed . therefore , chromosomal dna of s . suis type 2 was digested with alui . the 300 - 500 - bp fragments were ligated to smal - digested pphos2 . ligation mixtures were transformed to the phoa e . coli strain cc118 . transformants were plated on lb media supplemented with 5 - bromo - 4 - chloro - 3 - indolylfosfaat ( bcip , 50 μg / ml , boehringer , mannheim , germany ). blue colonies were purified on fresh lb / bcip plates to verify the blue phenotype . dna sequence analysis . dna sequences were determined on a 373a dna sequencing system ( applied biosystems , warrington , gb ). samples were prepared by using an abi / prism dye terminator cycle sequencing ready reaction kit ( applied biosystems ). sequencing data were assembled and analyzed using the macmollytetra program . custom - made sequencing primers were purchased from life technologies . hydrophobic stretches within proteins were predicted by the method of klein et al . ( 17 ). the blast program available on netscape navigator ™ was used to search for protein sequences related to the deduced amino acid sequences . construction of gene - specific knock - out mutants of s . suis . to construct the mutant strains 10cpsb and 10cpsef , we electrotransformed the pathogenic serotype 2 strain 10 ( 45 , 49 ) of s . suis with pcps 11 and pcps28 respectively . in these plasmids , the cpsb and cpsef genes were disturbed by the insertion of a spectinomycin - resistance gene . to create pcps11 , the internal 400 by pstibamhi fragment of the cpsb gene in pcps7 was replaced by the spc r gene . for this purpose , pcps7 was digested with psti and bamhi and ligated to the 1 , 200 - bp psti - bamhi fragment , containing the spc r gene ; from pic - spc . to construct pcps28 , we have used pic20r . in this plasmid we inserted the kpni - sali fragment from pcps17 ( resulting in pcps25 ) and the xbai - clai fragment from pcps20 ( resulting in pcps27 ). pcps27 was digested with psti and xhoi and ligated to the 1 , 200 - bp pstl - xhol fragment , containing the spc r gene of pic - spc . the electrotransformation to s . suis was carried out as described before ( 38 ). southern blotting and hybridization . chromosomal dna was isolated as described by sambrook et al . ( 36 ). dna fragments were separated on 0 . 8 % agarose gels and transferred to zeta - probe gt membranes ( bio - rad ) as described by sambrook et al . ( 36 ). dna probes were labeled with [( − 32 p ] dctp ( 3000 ci mmol − 1 ; amersham ) by use of a random primed labeling kit ( boehringer ). the dna on the blots was hybridized at 65 ° c . with appropriate dna probes as recommended by the supplier of the zeta - probe membranes . after hybridization , the membranes were washed twice with a solution of 40 mm sodium phosphate , ph 7 . 2 , 1 mm edta , 5 % sds for 30 min at 65 ° c . and twice with a solution of 40 mm sodium phosphate , ph 7 . 2 , 1 mm edta , 1 % sds for 30 min at 65 ° c . pcr . the primers used in the cps2j pcr correspond to the positions 13791 - 13813 and 14465 - 14443 in the s . suis cps2 locus . the sequences were : 5 ′- caaacgcaaggaattacggtatc - 3 ′ ( seq . id . no . 1 ) and 5 ′- gagtatctaaagaatgcctattg - 3 ′ ( seq . id . no . 2 ). the primers used for the cpsli pcr correspond to the positions 4398 - 4417 and 4839 - 4821 in the s . suis cps1 sequence . the sequences were : 5 ′- ggcggtctagcagatgctcg - 3 ′ ( seq . id . no . 3 ) and 5 ′- gcgaactgttagcaatgac - 3 ′ ( seq . id . no . 4 ). the primers used in the cps9h pcr correspond to the positions 4406 - 4126 and 4494 - 4475 in the s . suis cps9 sequence . the sequences were : 5 ′- ggctacatataatggaagccc3 ′ ( seq . id no . 5 ) and 5 ′- cggaagtatctgggctactg - 3 ′ ( seq . id . no . 6 ). construction of gene - specific knock - out mutants of s . suis . to construct the mutant strains 10cpsb and 10cpsef , we electrotransformed the pathogenic serotype 2 strain 10 of s . suis with pcps11 and pcps28 respectively . in these plasmids , the cpsb and cpsef genes were disturbed by the insertion of a spectinomycin - resistance gene . to create pcps11 , the internal 400 bp psti - bamhi fragment of the cpsb gene in pcps7 was replaced by the spc r gene . for this purpose , pcps7 was digested with psti and bamhi and ligated to the 1 , 200 - bp psti - bamhi fragment , containing the spc r gene , from pic - spc . to construct pcps28 , we have used pic20r . in this plasmid , we inserted the kpni - sali fragment from pcps17 ( resulting in pcps25 ) and the xbai - clai fragment from pcps20 ( resulting in pcps27 ). pcps27 was digested with psi and xhoi and ligated to the 1 , 200 - bp psti - xhoi fragment , containing the spc r gene of pic - spc . the electrotransformation to s . suis was carried out as described before ( 38 ). phagocytosis assay . phagocytosis assays were performed as described by leij et al . ( 23 ). briefly , to opsonize the cells , 10 7 s . suis cells were incubated with 6 % spf - pig serum for 30 min at 37 ° c . in a head - over - head rotor at 6 rpm . 10 7 am and 10 7 opsonized s . suis cells were combined and incubated at 37 ° c . under continuous rotation at 6 rpm . at 0 , 30 , 60 and 90 min , 1 - ml samples were collected and mixed with 4 ml of ice - cold emem to stop phagocytosis . phagocytes were removed by centrifugation for 4 min at 110 × g and 4 ° c . the number of colony - forming units , (“ cfu ”) in the supernatants was determined . control experiments were carried out simultaneously by combining 10 7 opsonized s . suis cells with emem ( without am ). killing assays . am ( 10 7 / ml ) and opsonized s . suis cells ( 10 7 / ml ) were mixed 1 : 1 and incubated for 10 min at 37 ° c . under continuous rotation at 6 rpm . ice - cold emem was added to stop further phagocytosis and killing . to remove extracellular s . suis cells , phagocytes were washed twice ( 4 min , 110 × g , 4 ° c .) and resuspended in 5 ml emem containing 6 % spf serum . the tubes were incubated at 37 ° c . under rotation at 6 rpm . after 0 , 15 , 30 , 60 and 90 min , samples were collected and mixed with ice - cold emem to stop further killing . the samples were centrifuged for 4 min at 110 × g at 4 ° c . and the phagocytic cells were lysed in emem containing 1 % saponine for 20 min at room temperature . the number of cfu in the suspensions was determined . pigs . germfree pigs , crossbreeds of great yorkshire and dutch landrace , were obtained from sows by caesarian sections . the surgery was performed in sterile flexible film isolators . pigs were allotted to groups , each consisting of 4 pigs , and were housed in sterile stainless steel incubators . experimental infections . pigs were inoculated intranasally with s . suis type 2 as described before . to predispose the pigs for infection with s . suis , five - day old pigs were inoculated intranasally with about 10 7 cfu of bordetella bronchiseptica strain 92932 . two days later , the pigs were inoculated intranasally with s . suis type 2 ( 10 6 cfu ). pigs were monitored twice daily for clinical signs of disease , such as fever , nervous signs and lameness . blood samples were collected three times a week from each pig . white blood cells were counted with a cell counter . to monitor infection with s . suis and b . bronchiseptica and to check for absence of contaminants , we collected swabs of nasopharynx and feces daily . the swabs were plated directly onto columbia agar containing 6 % horse blood . after three weeks , the pigs were killed and examined for pathological changes . tissue specimens from the central nervous system , serosae , and joints were examined bacteriologically and histologically as described herein ( 45 , 49 ). colonization of the serosae was scored positively when s . suis was isolated from the pericardium , thoracal pleura or the peritoneum . colonization of the joints was scored positively when s . suis was isolated from one or more joints ( 12 joints per animal were scored ). vaccination and challenge . one week old pigs were vaccinated intravenously with a dosage of 106 cfu of the s . suis strains 10cpsef or 10cpsb . three weeks later , the pigs were challenged intravenously with the pathogenic serotype 2 strain 10 ( 107 cfu ). disease monitoring , hematological , serological and bacteriological examinations as well as post - mortum examinations were as described before under experimental infections . electron microscopy . bacteria were prepared for electron microscopy as described by wagenaar et al . ( 50 ). shortly , bacteria were mixed with agarose nd ( boehringer ) of 37 ° c . to a concentration of 0 . 7 %. the mixture was immediately cooled on ice . upon gelifying , samples were cut into 1 to 1 . 5 mm slices and incubated in a fixative containing 0 . 8 % glutaraldehyde and 0 . 8 % osmiumtetraoxide . subsequently , the samples were fixed and stained with uranyl acetate by microwave stimulation , dehydrated and imbedded in eponaraldite resin . ultra - thin sections were counterstained with lead citrate and examined with a philips cm 10 electron microscope at 80 kv ( fig8 ). isolation of porcine alveolar macrophages ( am ). porcine am were obtained from the lungs of specific pathogen free (“ spf ”) pigs . lung lavage samples were collected as described by van leengoed et al . ( 43 ). cells were suspended in emem containing 6 % ( v / v ). spf - pig serum and adjusted to 10 7 cells per ml . the cps locus of s . suis type 2 was identified through a strategy developed for the genetic identification of exported proteins ( 13 , 31 ). in this system , we used a plasmid ( pphos2 ) containing a truncated alkaline phosphatase gene ( 13 ). the gene lacked the promoter sequence , the translational start site and the signal sequence . the truncated gene is preceded by a unique smal restriction site . chromosomal dna of s suis type 2 , digested with alui , was randomly cloned in this restriction site . because translocation of phoa across the cytoplasmic membrane of e . coli is required for enzymatic activity , the system can be used to select for s . suis fragments containing a promoter sequence , a translational start site and a functional signal sequence . among 560 individual e . coli clones tested , 16 displayed a dark blue phenotype when plated on media containing bcip . dna sequence analysis of the inserts from several of these plasmids was performed ( results not shown ) and the deduced amino acid sequences were analyzed . the hydrophobicity profile of one of the clones ( pphos7 , results not shown ) showed that the n - terminal part of the sequence resembled the characteristics of a typical signal peptide : a short hydrophilic n - terminal region is followed by a hydrophobic region of 38 amino acids . these data indicate that the phoa system was successfully used for the selection of s . suis genes encoding exported proteins . moreover , the sequences were analyzed for similarities present in the databases . the sequence of pphos7 showed a high similarity ( 37 % identity ) with the protein encoded by the cps14c gene of streptococcus pneumoniae ( 19 ). this strongly suggests that pphos7 contains a part of the cps operon of s . suis type 2 . cloning of the flanking cps genes . in order to clone the flanking cps genes of s . suis type 2 , the insert of pphos7 was used as a probe to identify chromosomal dna fragments which contain flanking cps genes . a 6 - kb hindiii fragment was identified and cloned in pkun19 . this yielded clone pcps6 ( fig1 , part c ). sequence analysis of the insert of pcps6 revealed that pcps6 most probably contained the 5 ′- end of the cps locus , but still lacked the 3 ′- end . therefore , sequences of the 3 ′- end of pcps6 were in turn used as a probe to identify chromosomal fragments containing cps sequences located further downstream . these fragments were also cloned in pkun19 , resulting in pcps17 . using the same system of chromosomal walking , we subsequently generated the plasmids pcps18 , pcps20 , pcps23 and pcps26 , containing downstream cps sequences . analysis of the cps operon . the complete nucleotide sequence of the cloned fragments was determined ( fig4 ). examination of the compiled sequence revealed the presence of at least 13 potential open reading frames ( orfs ), which were designated as orf 2y , orf2x and cps2a - cps2k ( fig1 , part a ; fig1 , part a ). moreover , a 14th , incomplete orf ( orf 2z ) was located at the 5 ′- end of the sequence . two potential promoter sequences were identified . one was located 313 bp ( locations 1885 - 1865 and 1884 - 1889 ) upstream of orf2x . the other potential promoter sequence was located 68 bp upstream of orf2y ( locations 2241 - 2236 and 2216 - 2211 ). orf2y is expressed in opposite orientation . between orfs 2y and 2z , the sequence contained a potential stem - loop structure , which could act as a transcription terminator . each orf is preceded by a ribosome - binding site and the majority of the orfs are very closely linked . the only significant intergenic gap was found between cps2g and cps2h ( 389 nucleotides ). however , no obvious promoter sequences or potential stem - loop structures were found in this region . these data suggest that orf2x and cps2a - cps2k are arranged as an operon . an overview of all orfs with their properties is shown in table 2 . the majority of the predicted gene products is related to proteins involved in polysaccharide biosynthesis . orf2z showed some similarity with the yits protein of bacillus subtilis . yits was identified during the sequence analysis of the complete genome of b . subtilis . the function of the protein is unknown . orf2y showed similarity with the ycxd protein of b . subtilis ( 53 ). based on the similarity between ycxd and mocr of rhizohium meliloti ( 33 ), ycxd was suggested to be a regulatory protein . orf2x showed similarity with the hypothetical yaaa proteins of haemophilus influenzae and e . coli . the function of these proteins is unknown . the gene products encoded by the cps2a , cps2b , cps2c and cps2d genes showed approximate similarity with the cpsa , cpsc , cpsd and cpsb proteins of several serotypes of streptococcus pneumoniae ( 19 ), respectively . this suggests similar functions for these proteins . hence , cps2a may have a role in the regulation of the capsular polysaccharide synthesis . cps2b and cps2c could be involved in the chain length determination of the type 2 capsule and cps2c can play an additional role in the export of the polysaccharide . the cps2d protein of s . suis is related to the cpsb protein of s . pneumoniae and to proteins encoded by genes of several other gram - positive bacteria involved in polysaccharide or exopolysaccharide synthesis , but their function is unknown ( 19 ). the protein encoded by the cps2e gene showed similarity to several bacterial proteins with glycosyltransferase activities cps14e and cps19fe of s . pneumoniae serotypes 14 and 19f ( 18 , 19 , 29 ), cpse of streptococcus salvarius ( x94980 ) and cpsd of streptococcus agalactiae ( 34 ). recently . kolkman et al . ( 18 ) showed that cps14e is a glucosyl - 1 - phosphate transferase that links glucose to a lipid carrier , the first step in the biosynthesis of the s . pneumoniae type 14 repeating unit . based on these data , a similar function may be fulfilled by cps2e of s . suis . the protein encoded by the cps2f gene showed similarity to the protein encoded by the rfbu gene of salmonella enteritica . ( 25 ). this similarity is most pronounced in the c - terminal regions of these proteins . the rfbu gene was shown to encode mannosyltransferase activity ( 25 ). the cps2g gene encoded a protein that showed moderate similarity with the rfbf gene product of campylohacter hyoilei ( 22 ), the epsf gene product of s . thermophilus ( 40 ) and the capm gene product of s . aureus ( 24 ). on the basis of similarity , the rfbf , epsf and capm genes are suggested to encode galactosyltransferase activities . hence , a similar glycosyltransferase activity could be fulfilled by the cps2g gene product . the cps2h gene encodes a protein that is similar to the n - terminal region of the lgtd gene product of haemophilus influenzae ( u32768 ). moreover , the hydrophobicity plots of cps2h and lgtd looked very similar in these regions ( data not shown ). based on sequence similarity , the igtd lgtd gene product was suggested to have glycosyltransferase activity ( u32768 ). the gene product encoded by the cps2i gene showed some similarity with a protein of actinobacillus actinomycetemcomitans ( ab002668 ). this protein is part of the gene cluster responsible for the serotype - b - specific antigen of a . actinomycetemcomitans . the function of the protein is unknown . the gene products encoded by the cps2j and cps2k genes showed significant similarities to the cps14j protein of s . pneumoniae . the cps14j gene of s . pneumoniae was shown to encode a β - 1 , 4 - galactosyltransferase activity . in s . pneumoniae , cpsj is responsible for the addition of the fourth ( i . e . last ) sugar in the synthesis of the s . pneumoniae serotype 14 polysaccharide ( 20 ). even some similarity was found between cps2j and cps2k ( fig2 , 25 . 5 % similarity ). this similarity was most pronounced in the n - terminal regions of the proteins ( fig7 ). recently , two small conserved regions were identified in the n - terminus of cps14j and cps14i and their homologues ( 20 ). these regions were predicted to be important for catalytic activity . both regions , dxs and dxdd ( fig2 ), were also found in cps2j and cps2k . distribution of the cps2 genes in other s . suis serotypes . to examine the relationship between the cps2 genes and cps genes in the other s . suis serotypes , we performed crosshybridization experiments . dna fragments of the individual cps2 genes were amplified by pcr , labeled with 32 p , and used to probe southern blots of chromosomal dna of the reference strains of the 35 different s . suis serotypes . large variations in the hybridization patterns were observed ( table 4 ). as a positive control , we used a probe specific for 16s rrna . the 16s rrna probe hybridized with all serotypes tested . however , none of the other genes tested were common in all serotypes . based on the genetic organization of the genes , we previously suggested that orfx and cpsa - cpsk genes are part of one operon and that the proteins encoded by these genes are all involved in polysaccharide biosynthesis . orfy and orfz are not a part of this operon , and their role in the polysaccharide biosynthesis is unclear . based on sequence similarity data , orfy may be involved in regulation of the cps2 genes . orfz is proposed to be unrelated to polysaccharide biosynthesis . probes specific for the orfz , orfy , orfx , cpsa , cpsb , cpsc and cpsd genes hybridized with most other serotypes . this suggests that the proteins encoded by these genes are not type - specific , but may perform more common functions in biosynthesis of the capsular polysaccharide . this confirms previous data which showed that the cps2a - cps2d genes showed strong similarity to cps genes of several serotypes of streptococcus pneumoniae . based on this similarity , cps2a is possibly a regulatory protein , whereas cps2b and cps2c may play a role in length determination and export of polysaccharide . the cps2e gene hybridized with dna of serotypes 1 , 2 , 14 and ½ . the cps2e gene showed a strong similarity to the cps14e gene of s . pneumoniae ( 18 ). t enzyme was shown to have a glucosyl - 1 - phosphate activity and catalyzed the transfer of glucose to a lipid carrier ( 18 ). these data indicate that a glycosyltransferase closely related to cps14e may be responsible for the first step in the biosynthesis of polysaccharide in the s . suis serotypes 1 , 2 , 14 and ½ . the cps2f , cps2g , cps2h , cps2i and cps2j genes hybridized with chromosomal dna of serotypes 2 and ½ only . the cps2g gene showed an additional weak hybridization signal with dna of serotype 34 . in agglutination tests , serotype ½ showed agglutination with sera specific for serotype 2 as well as with sera specific for serotype 1 . this suggests that serotype ½ shares antigenic determinants with both types 1 and 2 . the hybridization data confirmed these data . all putative glycosyltransferases present in serotype 2 are also present in serotype ½ . the cps2k gene showed a hybridization pattern similar to the cps2e gene . hybridization was observed with dna of serotypes 1 , 2 , 14 and ½ . taken together , these hybridization data show that the cps2 gene cluster can be divided into three regions : a central region containing the type - specific genes is flanked by two regions containing common genes for various serotypes . cloning of the type - specific cps genes of serotypes 1 and 9 . to clone the type - specific cps genes of s . suis serotype 1 , we used the cps2e gene as a probe to identify chromosomal dna fragments of type 1 which contain flanking cps genes . a 5 kb ecorv fragment was identified and cloned in pkun19 . this yielded pcps1 - 1 ( fig1 , part b ). this fragment was in turn used as a probe to identify an overlapping 2 . 2 kb hindiii fragment . pkun19 containing this hindiii fragment was designated pcps1 - 2 . the same strategy was followed to identify and clone the type - specific cps genes of serotype 9 . in this case , we used the cps2d gene as a probe . a 0 . 8 kb hindiii - xbai fragment was identified and cloned , yielding pcps9 - 1 ( fig1 , part c ). this fragment was in turn used as a probe to identify a 4 kb xbai fragment . pkun19 containing this 4 kb xbai fragment was designated pcps9 - 2 . analysis of the cloned cpsl genes . the complete nucleotide sequence of the inserts of pcps1 - 1 and pcps1 - 2 was determined ( fig5 ). examination of the sequence revealed the presence of five complete and two incomplete orfs ( fig1 , part b ). each orf is preceded by a ribosome - binding site . in accord with data obtained for the cps2 genes of serotype 2 , the majority of the orfs is very closely linked . the only significant gap ( 718 bp ) was found between cps1g and cps1h . no obvious promoter sequences or potential stem - loop structures could be found in this region . this suggests that , as in serotype 2 , the cps genes in serotype 1 are arranged in an operon . an overview of the orfs and their properties is shown in table 2 . as expected on the basis of the hybridization data ( table 4 ), the protein encoded by the cps1e gene was related to cps2e of s . suis type 2 ( identity of 86 %). the fragment cloned in pcps1 - 1 lacked the coding region for the first 7 amino acids of the cps1e gene . the protein encoded by the cps1f and cps1g genes showed strong similarity to the cps14f and cps14g proteins of streptococcus pneumoniae serotype 14 , respectively ( 20 ). the function of the cps14f is not completely clear , but it has been suggested that cps14f has a role in glycosyltransferase activity . the cps14g gene of s . pneumoniae was shown to encode β - 1 , 4 - galactosyltransferase activity . in s . pneumoniae type 14 , this activity is required for the second step in the biosynthesis of the oligosaccharide subunit ( 20 ). based on the similarity of the data , similar glyco syltransferase and enhancing activities are suggested for the cps1g and cps1f genes of s . suis type 1 . the protein encoded by the cps1h gene showed similarity to the cps14m protein of s . pneumoniae ( 20 ). based on sequence similarity , cps14h was proposed to be the polysaccharide polymerase ( 20 ). the protein encoded by the cps1i gene showed some similarity with the cps14j protein of s . pneumoniae ( 19 ). the cps14j gene was shown to encode a β - 1 , 4 - galactosyltransferase activity , responsible for the addition of the fourth ( i . e . last ) sugar in the synthesis of the s . pneumoniae serotype 14 polysaccharide . between cps1g and cps1h , a gap of 718 bp was found . this region revealed three small orfs . the three orfs were expressed in three different reading frames and were not preceded by potential ribosome binding sites , nor contained potential start sites . however , the three potential gene products encoded by this region showed some similarity with three successive regions of the c - terminal part of the epsk protein of streptococcus thermophilus ( 27 % identity , 40 ). the region related to the first 82 amino acids is lacking . analysis of the cloned cps9 genes . we also determined the complete nucleotide sequence of the inserts of pcps9 - 1 and pcps9 - 2 ( fig6 ). examination of the sequence revealed the presence of three complete and two incomplete orfs ( fig1 , part c ). as in serotypes 1 and 2 , all orfs are preceded by a ribosome - binding site and are very closely coupled . as suggested by the hybridization data ( table 4 ), the cps2d and cps9d proteins were highly related ( table 2 ). based on sequence comparisons , pcps9 - 1 lacked the first 27 amino acids of the cps9d protein . the protein encoded by the cps9e gene showed some similarity with the capd protein of staphylococcus aureus serotype 1 ( 24 ). based on sequence similarity data , the cap1d protein was suggested to be an epimerase or a dehydratase involved in the synthesis of n - acetylfiuctosamine or n - acetylgalactosamine ( 63 ). cps9f showed some similarity to the capm proteins of s . aureus serotypes 5 and 8 ( 61 , 64 , 65 ). based on sequence similarity data , cap5m and cap8m are proposed to be glycosyltransferases ( 63 ). the protein encoded by the cps9g gene showed some similarity to a protein of actinobacillus actinomycetemcomitans ( ab002668 — 4 ). this protein is part of a gene cluster responsible for the serotype - b specific serotype b - specific antigens of actinobacillus actinomycetemcomitans . the function of the protein is unknown . the protein encoded by the cps 9 h gene showed some similarity to the rfbb gene of yersinia enterolitica ( 68 ). the rfbb protein was shown to be essential for o - antigen synthesis , but the function of the protein in the synthesis of the 0 : 3 lipopolysaccharide is unknown . serotype 1 and serotype 9 specific 9 - specific cps genes . to determine whether the cloned fragments in pcps1 - 1 , pcps1 - 2 , pcps9 - 1 and pcps9 - 2 contained the type - specific genes for serotype 1 and 9 , respectively , cross - hybridization experiments were performed . dna fragments of the individual cps1 and cps9 genes were amplified by pcr , labeled with 32 p , and used to probe southern blots of chromosomal dna of the reference strains of the 35 different s . suis serotypes . the results are shown in table 5 . based on the data obtained with the cps2e probe ( table 4 ), the cps1e probe was expected to hybridize with chromosomal dna of s . suis serotypes 1 , 2 , 14 , 27 and ½ . the cps1h , cps9e and cps9f probes hybridized with most other serotypes however , the cps1f and cps1g and cps1i probes hybridized with chromosomal dna of serotypes 1 and 14 only . the cps9g and cps9h probes hybridized with serotype 9 only . these data suggest that the cps9g and cps9h probes are specific for serotype 9 and , therefore , could be useful tools for the development of rapid and sensitive diagnostic tests for s . suis type 9 infections . type specifictype - specific pcr . so far , the probes were tested on the 35 different reference strains only . to test the diagnostic value of the type - specific cps probes further , several other s . suis serotype 1 , 2 , ½ , 9 and 14 strains were used . moreover , since a pcr - based method would be even more rapid and sensitive than a hybridization test , we tested , whether we could use a pcr for the serotyping of the s . suis strains . the oligonucleotide primer sets were chosen within the cps2j , cps1i and cps9h genes . amplified fragments of 675 bp , 380 bp and 390 bp were expected , respectively . the results show that 675 bp fragments were amplified on type 2 and ½ strains using cps2j printers ; 380 bp fragments were amplified on type 1 and 14 strains using cps1i primers and 390 bp fragments were amplified on type 9 strains using cps9h primers . construction of mutants impaired in capsule production . to evaluate the role of the capsule of s . suis type 2 in pathogenesis , we constructed two isogenic mutants in which capsule production was disturbed . to construct mutant 10cpsb , pcps11 was used . in this plasmid , a part of the cps2b gene was replaced by the spectinomycin - resistance gene . to construct mutant strain 10cpsef , the plasmid pcps28 was used . in pcps28 , the 3 ′- end of cps2e gene , as well as the 5 ′- end , of cps2f gene , were replaced by the spectinomycin - resistance gene . pcps 11 and pcps28 were used to electrotransform strain 10 of s suis type 2 and spectinomycin - resistant colonies were selected . southern blotting and hybridization experiments were used to select double crossover integration events ( results not shown ). to test whether the capsular structure of the strains 10cpsb and 10cpsef was disturbed , we used a slide agglutination test using a suspension of the mutant strains in hyperimmune anti - s . suis type 2 serum ( 44 ). the results showed that even in the absence of serotype specific serotype - specific antisera , the bacteria agglutinated . this indicates that , in the mutant strains , the capsular structure was disturbed . to confirm this , thin sections of wild type and mutant strains were compared by electron microscopy . the results showed that , compared to the wild type ( fig3 , part a ), the amount of capsule produced by the mutant strains was greatly reduced ( fig3 , parts b and c ). almost no capsular material could be detected on the surface of the mutant strains . capsular mutants are sensitive to phagocytosis and killing by porcine alveolar macrophages (“ pam ”). the capsular mutants were tested for their ability to resist phagocytosis by pam in the presence of porcine spf serum . the wild type strain 10 seemed to be resistant to phagocytosis under these conditions ( fig9 a and 9b ). in contrast , the mutant strains were efficiently ingested by macrophages ( fig9 a and 9b ). after 90 min ., more than 99 . 7 % ( strain 10cpsb ) and 99 . 8 % ( strain 10cpsef ) of the mutant cells were ingested by the macrophages . moreover , as shown in fig9 a and 9b the ingested strains were efficiently killed by the macrophages . 90 - 98 % of all ingested cells were killed within 90 min . no differences could be observed between wild type and mutant strains . these data indicate that the capsule of s . suis type 2 efficiently protects the organism from uptake by macrophages in vitro . capsular mutants are less virulent for germfree piglets . the virulence properties of the wild - type and mutant strains were tested after experimental infection of newborn germ - free pigs ( 45 , 49 ). table 1 shows that specific and nonspecific signs of disease could be observed in all pigs inoculated with the wild type strain . moreover , all pigs inoculated with the wild type strain died during the course of the experiment or were killed because of serious illness or nervous disorders ( table 3 ). in contrast , the pigs inoculated with strains 10cpsb and 10cpsef showed no specific signs of disease and all pigs survived until the end of the experiment ( table 6 ). the temperature of the pigs inoculated with the wild type strain increased 2 days after inoculation and remained high until day 5 ( table 3 ). the temperature of the pigs inoculated with the mutant strains sometimes exceeded 40 ° c ., however , we could observe significant differences in the fever index ( i . e . percent of observations in an experimental group during which pigs showed fever (& gt ; 40 ° c .)) between pigs inoculated with wild type and mutant strains . all pigs showed increased numbers of polymorphonuclear leucocytes ( pmls ) (& gt ; 10 × 10 9 pmls per litre ) ( table 3 ). however , in pigs inoculated with the mutant strains , the percentage of samples with increased numbers of pmls was considerably lower . s . suis strains and b . bronchiseptica could be isolated from the nasopharynx and feces swab samples of all pigs from 1 day post - infection until the end of the experiment ( table 3 ). postmortem , the wild type strain could frequently be isolated from the central nervous system (“ cns ”), kidney , heart , liver , spleen , serosae , joints and tonsils . mutant strains could easily be recovered from the tonsils , but were never recovered from the kidney , liver or spleen . interestingly , low numbers of the mutant strains were isolated from the cns , the serosae , the joints , the lungs and the heart . taken together , these data strongly indicated that mutant s . suis strains , impaired in capsule production , are not virulent for young germfree pigs . we describe the identification and the molecular characterization of the cps locus , involved in the capsular polysaccharide biosynthesis , of s . suis . most of the genes seemed to belong to a single transcriptional unit , suggesting a coordinate control of these genes . we assigned functions to most of the gene products . we thereby identified regions involved in regulation ( cps2a ), chain length determination ( cps2b , c ), export ( cps2c ) and biosynthesis ( cps2e , f , g , h , j , k ). the region involved in biosynthesis is located at the center of the gene cluster and is flanked by two regions containing genes with more common functions . the incomplete orf2z gene was located at the 5 ′- end of the cloned fragment . orf2z showed some similarity with the yits protein of b . subtilis . however , because the function of the yits protein is unknown , this did not give us any information about the possible function of orf2z . because the orf2z gene is not a part of the cps operon , a role of this gene in polysaccharide biosynthesis is not expected . the orf2y protein showed some similarity with the ycxd protein of b . subtilis ( 53 ). the ycxd protein was suggested to be a regulatory protein . similarly , orf2y may be involved in the regulation of polysaccharide biosynthesis . the orf2x protein showed similarity with the yaaa proteins of h . influenzae and e . coli . the function of these proteins is unknown . in s . suis type 2 , the orf2x gene seemed to be the first gene in the cps2 operon . this suggests a role of orf2x in the polysaccharide biosynthesis . in h . influenzae and e . coli , however , these proteins are not associated with capsular gene clusters . the analysis of isogenic mutants impaired in the expression of orf2x should give more insight in the presumed role of orf2x in the polysaccharide biosynthesis of s . suis type 2 . the gene products encoded by the cps2e , cps2f , cps2g , cps2h , cps2j and cps2k genes showed little similarity with glycosyltransferases of several gram - positive or gram - negative bacteria ( 18 , 19 , 20 , 22 , 25 ). the cps2e gene product shows some similarity with the cps14e protein of s . pneumoniae ( 18 , 19 ). cps14e is a glucosyl - 1 - phosphate transferase that links glucose to a lipid carrier ( 18 ). in s . pneumoniae , this is the first step in the biosynthesis of the oligosaccharide repeating unit . the structure of the s . suis serotype 2 capsule contains glucose , galactose , rhamnose , n - acetyl glucosamine and sialic acid in a ratio of 3 : 1 : 1 : 1 : 1 ( 7 ). based on these data , we conclude that cps2e of s . suis has glucosyltransferase activity and is involved in the linkage of the first sugar to the lipid carrier . the c - terminal region of the cps2f gene product showed some similarity with the rfbu of salmonella enteritica . rfbu was shown to have mannosyltransferase activity ( 24 ). because mannosyl is not a component of the s . suis type 2 polysaccharide , a mannosyltransferase activity is not expected in this organism . nevertheless , cps2f encodes a glycosyltransferase with another sugar specificity . cps2g showed moderate similarity to a family of gene products suggested to encode galactosyltransferase activities ( 22 , 24 , 40 ). hence , a similar activity is shown for cps2g . cps2h showed some similarity with lgtd of h . influenzae ( u32768 ). because lgtd was proposed to have glycosyltransferase activity , a similar activity is fulfilled by cps2h . cps2j and cps2k showed similarity to cps14j of s . pneumoniae ( 20 ). cps2j showed similarity with cps14i of s . pneumoniae as well . cps14i was shown to have n - acetyl glucosaminyltransferase activity , whereas cps14j has a β - 1 , 4 - galactosyltransferase activity ( 20 ). in s . pneumoniae , cps14i is responsible for the addition of the third sugar and cps14j for the addition of the last sugar in the synthesis of the type 14 repeating unit ( 20 ). because the capsule of s . suis type 2 contains galactose as well as n - acetyl glucosamine components , galactosyltransferase as well as n - acetyl glucoaminyltransferase activities could be envisaged for the cps2j and cps2k gene products , respectively . as was observed for cps14i and cps14j , the n - termini of cps2j and cps2k showed a significant degree of sequence similarity . within the n - terminal domains of cps14i and cps14j , two small regions were identified , which were also conserved in several other glycosyltransferases ( 22 ). within these two regions , two asp residues were proposed to be important for catalytic activity . the two conserved regions , dxs and dxdd , were also found in cps2j and cps2k . the function of cps2i remains unclear . cps2i showed some similarity with a protein of a . actinomycetemcomitans . although this protein part is of the gene cluster responsible for the serotype - b - specific antigens , the function of the protein is unknown . we further describe the identification and characterization of the cps genes specific for s . suis serotypes 1 , 2 and 9 . after the entire cps2 locus of s . suis serotype 2 was cloned and characterized , functions for most of the cps2 gene products could be assigned by sequence homologies . based on these data , the glycosyltransferase activities , required for type specificity , could be located in the center of the operon . cross - hybridization experiments , using the individual cps2 genes as probes on chromosomal dnas of the 35 different serotypes , confirmed this idea . the regions containing the type - specific genes of serotypes 1 and 9 could be cloned and characterized , showing that an identical genetic organization of the cps operons of other s . suis serotypes exists . the cps1e , cps1f , cps1g , cps1h , and cps1i genes revealed a striking similarity with cps14e , cps14f , cps14g , cps14h and cps14j genes of s . pneumoniae . interestingly , s . pneumoniae serotype 14 is the serotype most commonly associated with pneumococcal infections in young children ( 54 ), whereas s . suis serotype 1 strains are most commonly isolated from piglets younger than 8 weeks ( 46 ). in s . pneumoniae , the cps14e , cps14g , cps14i and cps14j encode the glycosyltransferases required for the synthesis of the type 14 tetrameric repeating unit , showing that the cps1e , cps1g and cps1i genes encoded glycosyltransferases . the precise functions of these genes as well as the substrate specificities of the enzymes can be established . in s . pneumoniae , the cps14e gene was shown to encode a glucosyl - 1 - phosphate transferase catalyzing the transfer of glucose to a lipid carrier . moreover , cpse - like genes were found in s . pneumoniae serotypes 9n , 13 , 14 , 15b , 15c , 18f , 18a and 19f ( 60 ). cpse mutants were constructed in the serotypes 9n , 13 , 14 and 15b . all mutant strains lacked glucosyltransferase activity ( 60 ). moreover , in all these s . pneumoniae serotypes , the cpse gene seemed to be responsible for the addition of glucose to the lipid carrier . based on these data , we suggest that in s . suis type 1 , the cps1e gene may fulfil a similar function . the structure of the s . suis type 1 capsule is unknown , but it is composed of glucose , galactose , n - acetyl glucosamine , n - acetyl galactosamine and sialic acid in a ratio of 1 : 2 . 4 : 1 : 1 : 1 . 4 ( 5 ). therefore , a role of a cpse - like glucosyltransferase activity can easily be envisaged . cpse - like sequences were also found in serotypes 2 , ½ and 14 . for polysaccharide biosynthesis in s . pneumoniae type 14 , transfer of the second sugar of the repeating unit to the first lipid - linked sugar is performed by the gene products of cps14f and cps14g ( 20 ). similar to cps14f and cps14g , the s . suis type 1 prot cps1g may act as one glycosyltransferase performing the same reaction . cps14f and cps14g of s . pneumoniae showed similarity to the n - terminal half and c - terminal half of the spsk protein of sphingomonas ( 20 , 67 ), respectively . this suggests a combined function for both proteins . moreover , cps14f - and cps14g - like sequences were found in several serotypes of s . pneumoniae and these genes always seemed to exist together ( 60 ). the same was observed for s . suis type 1 . the cps1f and cps1g probes hybridized with type 1 and type 14 strains . according to the similarity found between the cps1h gene and the cps14h gene of s . pneumoniae ( 20 ), cps1h is expected to encode a polysaccharide polymerase . the protein encoded by the cps1i gene showed some similarity with the cps14j protein of s . pneumoniae ( 19 ). the cps14j gene was shown to encode a β - 1 , 4 - galactosyltransferase activity , responsible for the addition of the fourth ( i . e . last ) sugar in the synthesis of the s . pneumoniae serotype 14 polysaccharide . in s . suis type 2 , the proteins encoded by the cps2j and cps2k genes showed similarity to the cps14j protein . however , no significant homologies were found between cps2j , cps2k and cps1i . in the n - terminal regions of cps14j and cps14i , two small conserved regions , dxs and dxdd , were identified ( 19 ). these regions seemed to be important for catalytic activity ( 13 ). at the same positions in the sequence , cps2i contained the regions dxs and dxed . in the region between cps1g and cps1h , three small orfs were identified . since the orfs were expressed in three different reading frames , and did not contain potential start sites , expression is not expected . however , the three potential gene products encoded by this region showed some similarity with three successive regions of the c - terminal part of the epsk protein of streptococcus thermophilus ( 27 % identity , 40 ). the region related to the first 82 amino acids is lacking . the epsk protein was suggested to play a role in the export of the exopolysaccharide by rendering the polymerized exopolysaccharide more hydrophobic through a lipid modification . these data could suggest that the sequences in the region between cps1g and cps1h originated from epsk - like sequence . hybridization experiments showed that this epsk - like region is also present in other serotype 1 strains as well as in serotype 14 strains ( results not shown ). the function of most of the cloned serotype 9 genes can be established . based on sequence similarity data , the cps9e and cps9f genes could be glycosyltransferases ( 61 , 24 , 63 , 64 , 65 ). moreover , the cps9g and cps9h genes showed similarity to genes located in regions involved in polysaccharide biosynthesis , but the function of these genes is unknown ( 68 ). cross - hybridization experiments using the individual cps2 , cps1 and cps9 genes as probes showed that the cps9g and cps9h probes specifically hybridized with serotype 9 strains . therefore , these are useful as tools for the identification of s . suis type 9 strains both for diagnostic purposes as well as in epidemiological and transmission studies . we previously developed a pcr method which can be used to detect s . suis strains in nasal and tonsil swabs of pigs ( 62 ). the method was used to identify pathogenic ( ef - positive ) strains of s . suis serotype 2 . besides s . suis type 2 strains , serotype 9 strains are frequently isolated from organs of diseased pigs . however , until now , a rapid and sensitive diagnostic test was not available for type 9 strains . therefore , the type 9 specific probes 9 - specific probes or the type 9 specific 9 - specific pcr is of great diagnostic value . the cps1f , cps1g and cps1i probes hybridized with serotype 1 as well as with serotype 14 strains . in coagglutination tests , type 1 strains react with the anti - type 1 as well as with the anti - type 14 antisera ( 56 ). this suggests the presence of common epitopes between these serotypes . on the other hand , type 1 strains agglutinated only with anti - type 1 serum ( 56 , 57 ), indicating that it is possible to detect differences between those serotypes . the cps2f , cps2g , cps2h , cps2ji and cps2j probes hybridized with serotypes 2 and ½ only . serotype 34 showed a weak hybridizing signal with the cps2g probe . as shown in agglutination tests , type ½ strains react with sera directed against type 1 as well as with sera directed against type 2 strains ( 46 ). therefore , type ½ shared antigens with both types 1 and 2 . based on the hybridization patterns of serotype ½ strains with the cps1 and cps2 specific cps1 - and cps2 - specific genes , serotype ½ seemed to be more closely related to type 2 strains than to type 1 strains . in our current studies , we identify type - specific genes , primers or probes which are used for the discrimination of serotypes 1 , 14 and 2 and ½ and others of the 35 serotypes yet known . furthermore , type - specific genes , primers or probes can now easily be developed for yet unknown serotypes , once they become isolated . based on the established sequence , 11 genes , designated cps2l to cps2t , orf2u and orf2v , were identified . a gene homologous to genes involved in the polymerization of the repeating oligosaccharide unit ( cps2o ) as well as genes involved in the synthesis of sialic acid ( cps2p to cps2t ) were identified . moreover , hybridization experiments showed that the genes involved in the sialic acid synthesis are present in s . suis serotypes 1 , 2 , 14 , 27 and ½ . the “ cps2m ” and “ cps2n ” regions showed similarity to proteins involved in the polysaccharide biosynthesis of other gram - positive bacteria . however , these regions seemed to be truncated or were nonfunctional as the result of frame - shift or point mutations . at its 3 ′- end , the cps2 locus contained two insertional elements (“ orf2u ” and “ orf2v ”), both of which seemed to be non - functional . to clone the remaining part of the cps2 locus , sequences of the 3 ′- end of pcps26 ( fig1 , part c ) were used to identify a chromosomal fragment containing cps2 sequences located further downstream . this fragment was cloned in pkun19 , resulting in pcps29 . using a similar approach , we subsequently isolated the plasmids pcps30 and pcps34 containing downstream cps2 sequences ( fig1 , part c ). the complete nucleotide sequence of the cloned fragments was determined . examination of the compiled sequence revealed the presence of : a sequence encoding the c - terminal part of cps2k , six apparently functional genes ( designated cps2o - cps2t ) and the remnants of 5 different ancestral genes ( designated “ cps2l ” “ cps2m ”, “ cps2n ”, “ orf2u ” and “ orf2v ”). the latter genes seemed to be truncated or incomplete as the result of the presence of stop codons or frame - shift mutations ( fig1 , part a ). neither potential promoter sequences nor potential stem - loop structures could be identified within the sequenced region . a ribosome - binding site precedes each orf and the majority of the orfs are very closely linked . three intergenic gaps were found : one between “ cps2m ” and “ cps2n ” ( 176 nucleotides ), one between cps2o and cps2p ( 525 nucleotides ), and one between cps2t and “ orf2u ” ( 200 nucleotides ). these and our above data show that orf2x and cps2a - orf2t are part of a single operon . a list of all loci and their properties is shown in table 4 . the “ cps2l ” region contained three potential orfs of 103 , 79 and 152 amino acids , respectively , which were only separated from each other by stop codons . only the first orf is preceded by a potential ribosomal binding site and contained a methionine start codon . this suggests that “ cps2l ” originates from an ancestral cps2l gene , which coded for a protein of 339 amino acids . the function of this hypothetical cps2l protein remains unclear so far : no significant homologies were found between cps2l and proteins present in the data libraries . it is not clear whether the first orf of the “ cps2l ” region is expressed into a protein of 103 amino acids . the “ cps2m ” region showed homology to the n - terminal 134 amino acids of the neua proteins of streptococcus agalactiae and escherichia coli ( ab017355 , 32 ). however , although the “ cps2 m ” region contained a potential ribosome binding site , a methionine start codon was absent . compared with the s . agalactiae sequence , the atg start codon was replaced by a lysin encoding aag codon . moreover , the region homologous to the first 58 amino acids of the s . agalactiae neua ( identity 77 %) was separated from the region homologous to amino acids 59 - 134 of neua by a repeated dna sequence of 100 - bp ( see , herein ). in addition , the region homologous to amino acids 59 to 95 of neua ( identity 32 %) and the region homologous to the amino acids 96 to 134 of neua ( identity 50 %) were present in different reading frames . therefore , the partial and truncated neua homologue is probably nonfunctional in s . suis . the “ cps2n ” region showed homology to cpsj of s . agalactiae ( accession no . ab017355 ). however , sequences homologous to the first 88 amino acids of cpsj were lacking in s . suis . moreover , the homologous region was present in two different reading frames . the protein encoded by the cps2o gene showed homology to proteins of several streptococci involved in the transport of the oligosaccharide repeating unit ( accession no . ab017355 ), suggesting a similar function for cps2o . the proteins encoded by the cps2p , cps2s and cps2t genes showed homology to the neub , neud and neua proteins of s . agalactiae and e . coli ( accession no . ab017355 ). because the “ cps2m ” region also showed homology to neua of e . coli , the s . suis cps2 locus contains a functional neua gene ( cps2t ) as well as a nonfunctional (“ cps2m ”) gene . the mutual homology between these two regions showed an identity of 77 % at the amino acid level over amino acids 1 - 58 and 49 % over the amino acids 59 - 134 . cps2q and cps2r showed homology to the n - terminal and c - terminal parts of the neuc protein of s . agalactiae and e . coli , respectively . this suggests that the function of the s . agalactiae neuc protein in s . suis is likely fulfilled by two different proteins . in e . coli , the neu genes are known to be involved in the synthesis of sialic acid . neunac is synthesized from n - acetylmannosamine and phosphoenolpyruvate by neunac synthetase . subsequently , neunac is converted to cmp - neunac by the enzyme cmp - neunac synthetase . cmp - neunac is the substrate for the synthesis of polysaccharide . in e . coli , k1 neub is the neunac synthetase , and neua is the cmp - neunac synthetase . neuc has been implicated in the neunac synthesis , but its precise role is not known . the precise role of neud is not known . a role of the cps2p - cps2t proteins in the synthesis of sialic acid can easily be envisaged , since the capsule of s . suis serotype 2 is rich in sialic acid . in s . agalactiae , sialic acid has been shown to be critical to the virulence function of the type iii capsule . moreover , it has been suggested that the presence of sialic acid in the capsule of bacteria which can cause meningitis may be important for these bacteria to breach the blood - brain barrier . so far , however , the requirement of the sialic acid for virulence of s . suis remains unclear . “ orf2u ” and “ orf2v ” showed homology to proteins located on two different insertional elements . “ orf2u ” is homologous to is1194 of streptococcus thermophilus , whereas “ orf2v ” showed homology to a putative transposase of streptococcus pneumoniae . this putative transposase was recently found to be associated with the type 2 capsular locus of s . pneunioniae . compared with the original insertional elements in s . thermophilus and s . pneumoniae , both “ orf2u ” and “ orf2v ” are likely to be nonfunctional due to frame shift mutations within their coding regions . a striking observation was the presence of a sequence of 100 bp ( fig1 ) which was repeated three times within the cps2 operon . the sequence is highly conserved ( between 94 % and 98 %) and was found in the intergenic regions between cps2g and cps2h , within “ cps2m ” and between cps2o and cps2p . no significant homologies were found between this 100 - bp direct repeat sequence and sequences present in the data libraries , suggesting that the sequence is unique for s . suis . to examine the presence of sialic acid encoding genes in other s . suis serotypes , we performed cross - hybridization experiments . dna fragments of the individual cps2 genes were amplified by pcr , radiolabeled with 32p and hybridized to chromosomal dna of the reference strains of the 35 different s . suis serotypes . as a positive control , we used a probe specific for s . suis 16s rrna . the 16s rrna probe hybridized with almost equal intensities to all serotypes tested ( table 4 ). the “ cps2l ” sequence hybridized with dna of serotypes 1 , 2 , 14 and ½ . the “ cps2m ”, cps2o , cps2p , cps2q , cps2r , cps2s and cps2t genes hybridized with dna of serotypes 1 , 2 , 14 , 27 and ½ . because the cps2p - cps2t genes are most likely involved in the synthesis of sialic acid , these results suggest that sialic acid is also a part of the capsule in the s . suis serotypes 1 , 2 , 14 , 27 and ½ . this is in agreement with the finding that the serotypes 1 , 2 and ½ possess a capsule that is rich in sialic acid . although the chemical compositions of the capsules of serotypes 14 and 27 are unknown , recent agglutination studies using sialic acid - binding lectins suggested the presence of sialic acid in s . suis serotype 14 , but not in serotype 27 . in these studies , sialic acid was also detected in serotypes 15 and 16 . since the latter observation is not in agreement with our hybridization studies , it might be that other genes , not homologous to the cps2p - cps2t genes , are responsible for the sialic acid synthesis in serotypes 15 and 16 . a probe based on “ cps2n ” sequences hybridized with dna from serotypes 1 , 2 , 14 and ½ . a probe specific for “ orf2u ” hybridized with serotypes 1 , 2 , 7 , 14 , 24 , 27 , 32 , 34 , and ½ , whereas a probe specific for “ orf2v ” hybridized with many different serotypes . in addition , we prepared a probe specific for the 100 - bp direct repeat sequence . this probe hybridized with the serotypes 1 , 2 , 13 , 14 , 22 , 24 , 27 , 29 , 32 , 34 and ½ ( table 4 ). to analyze the number of copies of the direct repeat sequence within the s . suis serotype 2 chromosome , a southern blot hybridization and analysis was performed . therefore , chromosomal dna of s . suis serotype 2 was digested with ncoi and hybridized with a 32p - labeled direct repeat sequence . only one hybridizing fragment , containing the three direct repeats present on the cps2 locus , was found ( results not shown ). this indicates that the 100 - bp direct repeat sequence is only associated with the cps2 locus . in s . pneumoniae , a 115 - bp long repeated sequence was found to be associated with the capsular genes of serotypes 1 , 3 , 14 and 19f . in s . pneumoniae , this 115 - bp sequence was also found in the vicinity of other genes involved in pneumococcal virulence ( hyaluronidase and neuraminidase genes ). a regulatory role of the 115 - bp sequence in coordinate control of these virulence - related genes was suggested . to study the role of the capsule in resistance to phagocytosis and in virulence , we constructed two isogenic mutants in which capsule synthesis was disturbed . in 10cpsb , the cps2b gene was disturbed by the insertion of an antibiotic - resistance gene , whereas in 10cpsef , parts of the cps2e and cps2f genes were replaced . both mutant strains seemed to be completely unencapsulated . because the cps2 genes seemed to be part of an operon , polar effects cannot be excluded . therefore , these data did not give any information about the role of cps2b , cps2e or cps2f in the polysaccharide biosynthesis . however , the results clearly show that the capsular polysaccharide of s . suis type 2 is a surface component with antiphagocytic activity . in vitro wild type encapsulated bacteria are ingested by phagocytes at a very low frequency , whereas the mutant unencapsulated bacteria are efficiently ingested by porcine macrophages . within 2 hours , over 99 . 6 % of mutant bacteria were ingested and over 92 % of the ingested bacteria were killed . intracellularly , wild type as well as mutant strains seemed to be killed with the same efficiency . this suggests that the loss of capsular material is associated with loss of capacity to resist uptake by macrophages . this loss of resistance to in vitro phagocytosis was associated with a substantial attenuation of the virulence in germfree pigs . all pigs inoculated with the mutant strains survived the experiment and did not show any specific clinical signs of disease . only some aspecific clinical signs of disease could be observed . moreover , mutant bacteria could be reisolated from the pigs . this supports the idea that , as in other pathogenic streptococci , the capsule of s . suis acts as an important virulence factor . transposon mutants prepared by charland impaired in the capsule production showed a reduced virulence in pigs and mice . to construct these mutants , the type 2 reference strain s735 was used . we previously showed that this strain is only weakly virulent for young pigs . moreover , the insertion site of the transposon is unsolved so far . as a further example herein , a rapid pct test for streptococcus suis type 7 is described . recent epidemiological studies on streptococcus suis infections in pigs indicated that , besides serotypes 1 , 2 and 9 , serotype 7 is also frequently associated with diseased animals . for the latter serotype , however , no rapid and sensitive diagnostic methods are available . this hampers prevention and control programs . here we describe the development of a type - specific pcr test for the rapid and sensitive detection of s . suis serotype 7 . the test is based on dna sequences of capsular ( cps ) genes specific for serotype 7 . these sequences could be identified by cross - hybridization of several individual cps genes with the chromosomal dnas of 35 different s . suis serotypes . streptococcus suis is an important cause of meningitis , septicemia , arthritis and sudden death in young pigs ( 69 , 70 ). it can however , also cause meningitis in man ( 71 ). attempts to control the disease are still hampered by the lack of sufficient knowledge about the epidemiology of the disease and the lack of effective vaccines and sensitive diagnostics . s . suis strains can be identified and classified by their morphological , biochemical and serological characteristics ( 70 , 73 , 74 ). serological classification is based on the presence of specific antigenic determinants . isolated and biochemically characterized s . suis cells are agglutinated with a panel of specific sera . these typing methods are very laborious and time - consuming and can only be performed on isolated colonies . moreover , it has been reported that non - specific cross - reactions may occur among different types of s . suis ( 75 , 76 ). so far , 35 different serotypes have been described ( 7 , 78 , 79 ). s . suis serotype 2 is the most prevalent type isolated from diseased pigs , followed by serotypes 9 and 1 . however , recently , serotype 7 strains were also frequently isolated from diseased pigs ( 80 , 81 , 82 ). this suggests that infections with s . suis serotype 7 strains seem to be an increasing problem . moreover , the virulence of s . suis serotype 7 strains was confirmed by experimental infection of young pigs ( 83 ). recently , rapid and sensitive pcr assays specific for serotypes 2 ( and ½ ), 1 ( and 14 ) and 9 were developed ( 84 ). these assays were based on the cps loci of s . suis serotypes 2 , 1 and 9 ( 84 , 85 ). however , until now , no rapid and sensitive diagnostic test was available for s . suis serotype 7 . herein we describe the development of a pcr test for the rapid and sensitive detection of s . suis serotype 7 strains . the test is based on dna sequences which form a part of the cps locus of s . suis serotype 7 . compared with the serological serotyping methods , the pcr assay was a rapid , reliable and sensitive assay . therefore , this test , in combination with the pcr tests which we previously developed for serotypes 1 , 2 and 9 , will undoubtedly contribute to a more rapid and reliable diagnosis of s . suis and may facilitate control and eradication programs . the bacterial strains and plasmids used in this study are listed in table 7 . the s . suis reference strains were obtained from m . gottschalk , canada . s . suis strains were grown in todd - hewitt broth ( code cm189 , oxoid ), and plated on columbia agar blood base ( code cm331 , oxoid ) containing 6 % ( v / v ) horse blood . e . coli strains were grown in luria broth ( 86 ) and plated on luria broth containing 1 . 5 % ( w / v ) agar . if required , ampicillin was added to the plates . the s . suis strains were serotyped by the slide agglutination test with serotype - specific antibodies ( 70 ). routine dna manipulations and pcr reactions were performed as described by sambrook et al . ( 88 ). blotting and hybridization were performed as described previously ( 84 , 86 ). dna sequences were determined on a 373a dna sequencing system ( applied biosystems , warrington , gb ). samples were prepared by use of an abi / prism dye terminator hcycle sequencing ready reaction kit ( applied biosystems ). custom - made sequencing primers were purchased from life teclmologies . sequencing data were assembled and analyzed using the mcmollytetra program . the blast program was used to search for protein sequences homologous to the deduced amino acid sequences . the primers used for the cps7h pcr correspond to the positions 3334 - 3354 and 3585 - 3565 in the s . suis cps7 locus . the reaction mixtures contained 10 mm tris - hcl , ph 8 . 3 ; 1 . 5 mnm mgcl2 ; 50 mm kcl ; 0 . 2 mm of each of the four deoxynucleotide triphosphates ; 1 microm of each of the primers and 1u of amplitaq gold dna polymerase ( perkin elmer applied biosystems , n . j .). dna amplification was carried out in a perkin elmer 9600 thermal cycler and the program consisted of an incubation for 10 min at 95 ° c . and 30 cycles of 1 min at 95 ° c ., 2 min at 56 ° c . and 2 min at 72 ° c . to isolate the type - specific cps genes of s . suis serotype 7 , we used the cps9e gene of serotype 9 as a probe to identify chromosomal dna fragments of type 7 containing homologous dna sequences ( 84 ). a 1 . 6 - kb psti fragment was identified and cloned in pkun19 . this yielded pcps7 - 1 ( fig1 , part c ). in turn , this fragment was used as a probe to identify an overlapping 2 . 7 kb scai - clai fragment . pgem7 containing the latter fragment was designated pcps7 - 2 ( fig1 , part c ). the complete nucleotide sequences of the inserts of pcps7 - 1 , pcps7 - 2 were determined . examination of the cps7 sequence revealed the presence of two complete and two incomplete open reading frames ( orfs ) ( fig1 , part c ). all orfs are preceded by a ribosome - binding site . in accord with the data obtained for the cps1 , cps2 and cps9 genes of serotypes 1 , 2 and 9 , respectively , the type 7 orfs are very closely linked to each other . the only significant intergenic gap was that found between cps7e and cps7f ( 443 nucleotides ). no obvious promoter sequences or potential stem - loop structures were found in this region . this suggests that , as in serotypes 1 , 2 and 9 , the cps genes in serotype 7 form part of an operon . an overview of the orfs and their properties is shown in table 8 . as expected on the basis of the hybridization data ( 84 ), the cps9e and cps7e proteins showed a high similarity ( identity 99 %. table 8 ). based on sequence comparisons between cps9e and cps7e , the psti fragment of pcps7 - 1 lacks the region encoding the first 371 codons of cps7e . the c - terminal part of the protein encoded by the cps7f gene showed some similarity with the bp1g protein of bordetella pertussis ( 88 ), as well as with the c - terminal part of s . suis cps2e ( 85 ). both bp1g and cps2e were suggested to have glycosyltransferase activity and are probably involved in the linkage of the first sugar to the lipid carrier ( 85 , 88 ). the protein encoded by the cps7g gene showed similarity with the bp1f protein of bordetella pertussis ( 88 ). b1pf is likely to be involved in the biosynthesis of an amino sugar , suggesting a similar function for cps7g . the protein encoded by the cps7h gene showed similarity with the wbdn protein of e . coli ( 89 ) as well as with the n - terminal part of the cps2k protein of s . suis ( 81 ). both wbdn and cps2k were suggested to have glycosyltransferase activity ( 85 , 89 ). to determine whether the cloned fragments in pcps7 - 1 and pcps7 - 2 contained serotype 7 - specific dna sequences , cross - hybridization experiments were performed . dna fragments of the individual cps7 genes were amplified by pcr , labeled with 32p , and used to probe spot blots of chromosomal dna of the reference strains of 35 different s . suis serotypes . the results are summarized in table 9 . as expected , based on the data obtained with the cps9e probe ( 84 ), the cps7e probe hybridized with chromosomal dna of many different s . suis serotypes . the cps7f and cps7g probes showed hybridization with chromosomal dna of s . suis serotypes 4 , 5 , 7 , 17 , and 23 . however , the cps7h probe hybridized with chromosomal dna of serotype 7 only , indicating that this gene is specific for serotype 7 . we tested whether we could use pcr instead of hybridization for the typing of the s . suis serotype 7 strains . for that purpose , we selected an oligonucleotide primer set within the cps7h gene with which an amplified fragment of 251 - bp was expected . in addition , we included in our analysis several s . suis serotype 7 strains , other than the reference strain . these strains were obtained from different countries and were isolated from different organs ( table 7 ). the results show that indeed a fragment of about 250 - bp was amplified with all type 7 strains used ( fig1 , part b ), whereas no pcr products were obtained with serotype 1 , 2 and 9 strains ( fig1 , part a ). this suggests that the pcr test , as described here , is a rapid diagnostic tool for the identification of s . suis serotype 7 strains . until now , such a diagnostic test was not available for serotype 7 strains strains . together with the recently developed pcr assays for serotypes 1 , 2 , ½ , 14 and 9 , this assay may be an important diagnostic tool to detect pigs carrying serotype 2 , ½ , 1 , 14 , 9 and 7 strains and may facilitate control and eradication programs . 3 . arrecubieta , c ., r . lopez , and e . garcia . 1994 . molecular characterization of cap3a , a gene from the operon required for the synthesis of the capsule of streptococcus pneumoniae type 3 : sequencing of mutations responsible for the unencapsulated phenotype and localization of the capsular cluster on the pneumococcal chromosome . j . bacteriol . 176 : 6375 - 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