Hemagglutination activities of group B, C, D, and G streptococci: demonstration of novel sugar-specific cell-binding activities in Streptococcus suis

The binding mechanism of the virulence factor Streptococcus suis adhesin P subtype to globotetraosylceramide is associated with systemic disease

Streptococcus suis is part of the pig commensal microbiome but strains can also be pathogenic, causing pneumonia and meningitis in pigs as well as zoonotic meningitis. According to genomic analysis, S. suis is divided into asymptomatic carriage, respiratory and systemic strains with distinct genomic signatures. Because the strategies to target pathogenic S. suis are limited, new therapeutic approaches are needed. The virulence factor S. suis adhesin P (SadP) recognizes the galabiose Galα1-4Gal-oligosaccharide. Based on its oligosaccharide fine specificity, SadP can be divided into subtypes P_N and P_O We show here that subtype P_N is distributed in the systemic strains causing meningitis, whereas type P_O is found in asymptomatic carriage and respiratory strains. Both types of SadP are shown to predominantly bind to pig lung globotriaosylceramide (Gb3). However, SadP adhesin from systemic subtype P_N strains also binds to globotetraosylceramide (Gb4). Mutagenesis studies of the galabiose-binding domain of type P_N SadP adhesin showed that the amino acid asparagine 285, which is replaced by an aspartate residue in type P_O SadP, was required for binding to Gb4 and, strikingly, was also required for interaction with the glycomimetic inhibitor phenylurea-galabiose. Molecular dynamics simulations provided insight into the role of Asn-285 for Gb4 and phenylurea-galabiose binding, suggesting additional hydrogen bonding to terminal GalNAc of Gb4 and the urea group. Thus, the Asn-285-mediated molecular mechanism of type P_N SadP binding to Gb4 could be used to selectively target S. suis in systemic disease without interfering with commensal strains, opening up new avenues for interventional strategies against this pathogen.

Fluorescence Imaging of Streptococcus pneumoniae with the Helix pomatia agglutinin (HPA) As a Potential, Rapid Diagnostic Tool

Streptococcus pneumoniae is a common human pathogen and a major causal agent of life-threatening infections that can either be respiratory or non-respiratory. It is well known that the Helix pomatia (edible snail) agglutinin (HPA) lectin shows specificity for terminal αGalNAc residues present, among other locations, in the Forssman pentasaccharide (αGalNAc1→3βGalNAc1→3αGal1→4βGal1→4βGlc). Based on experiments involving choline-independent mutants and different growth conditions, we propose here that HPA recognizes the αGalNAc terminal residues of the cell wall teichoic and lipoteichoic acids of S. pneumoniae. In addition, experimental evidence showing that pneumococci can be specifically labeled with HPA when growing as planktonic cultures as well as in mixed biofilms of S. pneumoniae and Haemophilus influenzae has been obtained. It should be underlined that pneumococci were HPA-labeled despite of the presence of a capsule. Although some non-pneumococcal species also bind the agglutinin, HPA-binding combined with fluorescence microscopy constitutes a suitable tool for identifying S. pneumoniae and, if used in conjunction with Gram staining and/or other suitable technique like antigen detection, it may potentially facilitate a fast and accurate diagnosis of pneumococcal infections.

Towards bacterial adhesion-based therapeutics and detection methods

Bacterial adhesion is an important first step towards bacterial infection and plays a role in colonization, invasion and biofilm formation.

Use of tetravalent galabiose for inhibition of streptococcus suis serotype 2 infection in a mouse model

Streptococcus suis is an important swine pathogen associated with a variety of infections such as meningitis, arthritis and septicemia. The bacterium is zoonotic and has been found to cause meningitis especially in humans occupationally exposed to infected pigs. Since adhesion is a prerequisite for colonization and subsequent infection, anti-adhesion treatment seems a natural alternative to traditional treatment with antibiotics. In order to optimize the inhibitory potency a multivalency approach was taken in the inhibitor design. A synthetic tetravalent galabiose compound was chosen which had previously shown promising anti-adhesion effects with S. suis in vitro. The aim of this study was to evaluate the in vivo effects of the compound using an infection peritonitis mouse model. As such S. suis serotype 2 infection and treatment were tested in vivo and the effects were compared to the effect of treatment with penicillin.

Identification of a novel streptococcal adhesin P (SadP) protein recognizing galactosyl-α1-4-galactose-containing glycoconjugates: convergent evolution of bacterial pathogens to binding of the same host receptor

Bacterial adhesion is often a prerequisite for infection, and host cell surface carbohydrates play a major role as adhesion receptors. Streptococci are a leading cause of infectious diseases. However, only few carbohydrate-specific streptococcal adhesins are known. Streptococcus suis is an important pig pathogen and a zoonotic agent causing meningitis in pigs and humans. In this study, we have identified an adhesin that mediates the binding of S. suis to galactosyl-α1-4-galactose (Galα1-4Gal)-containing host receptors. A functionally unknown S. suis cell wall protein (SSU0253), designated here as SadP (streptococcal adhesin P), was identified using a Galα1-4Gal-containing affinity matrix and LC-ESI mass spectrometry. Although the function of the protein was not previously known, it was recently identified as an immunogenic cell wall protein in a proteomic study. Insertional inactivation of the sadP gene abolished S. suis Galα1-4Gal-dependent binding. The adhesin gene sadP was cloned and expressed in Escherichia coli. Characterization of its binding specificity showed that SadP recognizes Galα1-4Gal-oligosaccharides and binds its natural glycolipid receptor, GbO(3) (CD77). The N terminus of SadP was shown to contain a Galα1-Gal-binding site and not to have apparent sequence similarity to other bacterial adhesins, including the E. coli P fimbrial adhesins, or to E. coli verotoxin or Pseudomonas aeruginosa lectin I also recognizing the same Galα1-4Gal disaccharide. The SadP and E. coli P adhesins represent a unique example of convergent evolution toward binding to the same host receptor structure.

Screening of binding activity of Streptococcus pneumoniae, Streptococcus agalactiae and Streptococcus suis to berries and juices

Antiadhesion therapy is a promising approach to the fight against pathogens. Antibiotic resistance and the lack of effective vaccines have increased the search for new methods to prevent infectious diseases. Previous studies have shown the antiadhesion activity of juice from cultivated cranberries (Vaccinium macrocarpon Ait.) against bacteria, especially E. coli. In this study, the binding of two streptococcal strains, Streptococcus pneumoniae and Streptococcus agalactiae, to molecular size fractions (FI, FII and FIII, <10 kDa, 10-100 kDa, and >100 kDa, respectively) of berries and berry and fruit juices from 12 plant species were studied using a microtiter well assay. For Streptococcus suis a hemagglutination inhibition assay was used. In general, binding activity was detected especially to wild cranberry (Vaccinium oxycoccos L.) and to other Vaccinium species. S. pneumoniae cells bound most to cranberry juice fraction FI and S. agalactiae cells to cranberry fraction FIII. Hemagglutination induced by S. suis was most effectively inhibited by cranberry fraction FII. NMR spectra of some characteristic active and non-active fractions were also measured. They indicate that fractions FII and FIII contained proanthocyanidins and/or other phenolic compounds. The results suggest Vaccinium berries as possible sources of antiadhesives against bacterial infections.

Structural and biological properties of the carbohydrate units of nervous tissue glycoproteins

We have identified structures in nervous tissue glycoproteins that are novel for glycoproteins in general or enriched in nervous tissue or cells of neural origin. These include: (alpha 2-8)-linked polysialic acid units, the linear form of poly-N-acetyllactosamine glycans, the sialylated X antigen determinant NeuAc(alpha 2-3)-Gal(beta 1-4) [Fuc(alpha 1-3)]GlcNAc, a series of Man-O-Ser(Thr)-linked glycans, and the O-glycosidically linked disaccharide unit Gal(alpha 1-3)GalNAc. The polysialic and poly-N-acetyllactosamine glycans are also developmentally regulated. The polysialic acid units in the cell adhesion molecule N-CAM. The poly-N-acetyllactosamine units occur in the adhesion molecule NILE (which is immunologically similar to Ng-CAM and L1) and in some other components revealed by a cell surface-labelling method specific for these glycans. The mannose-linked glycans occur in a chondroitin sulphate proteoglycan involved in neuron-glia interactions. Other biological interactions of the carbohydrates include their serving as bacterial receptors in meningitis, their serving as models for molecular mimicry by the capsules of meningitis-causing bacteria, and the role of some structures as antigens in autoimmune conditions. At the molecular level, two types of mechanisms are suggested for the glycans in molecular interactions: they may function either as mediators of interactions by serving as specific recognition ligands, or as modulators of the interactions determined by polypeptides or other molecules.

Inhibition of P-fimbriated Escherichia coli adhesion by multivalent galabiose derivatives studied by a live-bacteria application of surface plasmon resonance

OBJECTIVES

Uropathogenic P-fimbriated Escherichia coli adheres to host cells by specific adhesins recognizing galabiose (Galalpha1-4Gal)-containing structures on cell surfaces. In search of agents inhibiting this first step of infection, the inhibition potency of a set of synthetic mono- and multivalent galabiose compounds was evaluated. In order to mimic the flow conditions of natural infections, a live-bacteria application of surface plasmon resonance (SPR) was established.

METHODS AND RESULTS

For the measurement of the binding of E. coli to a surface containing galabiose, live bacteria were injected over the flow cell, and the inhibition of adhesion caused by the galabiose inhibitors was recorded. Quantitative binding data were recorded in real-time for each inhibitor. The results were compared with those of conventional static haemagglutination and ELISA-based cell adhesion assays. Compared with the Gram-positive Streptococcus suis bacteria, which also bind to galabiose and whose binding inhibition is strongly dependent on the multivalency of the inhibitor, E. coli inhibition was only moderately affected by the valency. However, a novel octavalent compound was found to be the most effective inhibitor of E. coli PapG(J96) adhesion, with an IC50 value of 2 microM.

CONCLUSIONS

Measurement of bacterial adhesion by SPR is an efficient way to characterize the adhesion of whole bacterial cells and allows the characterization of the inhibitory potency of adhesion inhibitors under dynamic flow conditions. Under these conditions, multivalency increases the anti-adhesion potency of galabiose-based inhibitors of P-fimbriated E. coli adhesion and provides a promising approach for the design of high-affinity anti-adhesion agents.

Hemagglutinating and hemolytic activities of Enterococcus faecalis strains isolated from different human clinical sources

A total of 95 Enterococcus faecalis strains isolated from different human clinical sources were investigated for hemagglutinating activities and hemolysin (Hly) production in the presence of erythrocytes from a wide range of species. MRHA (mannose-resistant hemagglutination) activity was found in all clinical strains tested in this study. MRHA of E. faecalis strains isolated from different sources was most frequently observed with human (both group O and A) and guinea pig erythrocytes. None of the strains agglutinated horse erythrocytes in the presence of 1% alpha-D-mannose. It should be emphasized that our data indicate the absence of a relationship between sources and MRHA. In contrast, all 95 strains investigated in this report were negative for MSHA (mannose-sensitive hemagglutination) activity. Regarding hemolysin production, it was seen that E. faecalis, and particularly urinary strains, preferably lysed horse erythrocytes. On the other hand, none of the 95 clinical strains tested in this study showed hemolytic activity against bovine and sheep erythrocytes. In general, these results show that E. faecalis strains isolated from different clinical sources possessed a diversity of hemagglutinins and a limited repertoire of hemolysin activities.

Fluid- or surface-phase human salivary scavenger protein gp340 exposes different bacterial recognition properties

Salivary scavenger receptor cysteine-rich protein gp340 aggregates streptococci and other bacteria as part of the host innate defense system at mucosal surfaces. In this article, we have investigated the properties of fluid-phase gp340 and hydroxylapatite surface-adsorbed gp340 in aggregation and adherence, respectively, of viridans group streptococci (e.g., Streptococcus gordonii and Streptococcus mutans), non-viridans group streptococci (e.g., Streptococcus pyogenes and Streptococcus suis), and oral Actinomyces. Fluid-phase gp340 and surface-phase gp340 bioforms were differentially recognized by streptococci, which formed three phenotypic groupings according to their modes of interaction with gp340. Group I streptococci were aggregated by and adhered to gp340, and group II streptococci preferentially adhered to surface-bound gp340, while group III streptococci were preferentially aggregated by gp340. Each species of Streptococcus tested was found to contain strains representative of at least two of these gp340 interaction groupings. The gp340 interaction modes I to III and sugar specificities of gp340 binding strains coincided for several species. Many gp340 interactions were sialidase sensitive, and each of the interaction modes (I to III) for S. gordonii was correlated with a variant of sialic acid specificity. Adherence of S. gordonii DL1 (Challis) to surface-bound gp340 was dependent upon expression of the sialic acid binding adhesin Hsa. However, aggregation of cells by fluid-phase gp340 was independent of Hsa and involved SspA and SspB (antigen I/II family) polypeptides. Conversely, both gp340-mediated aggregation and adherence of S. mutans NG8 involved antigen I/II polypeptide. Deletion of the mga virulence regulator gene in S. pyogenes resulted in increased cell aggregation by gp340. These results suggest that salivary gp340 recognizes different bacterial receptors according to whether gp340 is present in the fluid phase or surface bound. This phase-associated differential recognition by gp340 of streptococcal species of different levels of virulence and diverse origins may mediate alternative host responses to commensal or pathogenic bacterial phenotypes.

Molecular basis of H2O2 resistance mediated by Streptococcal Dpr. Demonstration of the functional involvement of the putative ferroxidase center by site-directed mutagenesis in Streptococcus suis

H(2)O(2) is an unavoidable cytotoxic by-product of aerobic life. Dpr, a recently discovered member of the Dps protein family, provides a means for catalase-negative bacteria to tolerate H(2)O(2). Potentially, Dpr could bind free intracellular iron and thus inhibit the Fenton chemistry-catalyzed formation of toxic hydroxyl radicals (H(2)O(2) + Fe(2+) --> (.)OH + (-)OH + Fe(3+)). We explored the in vivo function of Dpr in the catalase- and NADH peroxidase-negative pig and human pathogen Streptococcus suis. We show that: (i) a Dpr allelic exchange knockout mutant was hypersensitive ( approximately 10(6)-fold) to H(2)O(2), (ii) Dpr incorporated iron in vivo, (iii) a putative ferroxidase center was present in Dpr, (iv) single amino acid substitutions D74A or E78A to the putative ferroxidase center abolished the in vivo iron incorporation, and (v) the H(2)O(2) hypersensitive phenotype was complemented by wild-type Dpr or by a membrane-permeating iron chelator, but not by the site-mutated forms of Dpr. These results demonstrate that the putative ferroxidase center of Dpr is functionally active in iron incorporation and that the H(2)O(2) resistance is mediated by Dpr in vivo by its iron binding activity.

Interactions between Streptococcus suis serotype 2 and different epithelial cell lines

Streptococcus suis is an important swine pathogen responsible for cases of sudden death, septicaemia, meningitis, endocarditis and pneumonia. It is also recognized as a zoonotic agent in people occupationally exposed to pigs or pig products. Knowledge on virulence factors of S. suis serotype 2 is limited and the pathogenesis of the infection is poorly understood. It has been suggested that the disease due to S. suis serotype 2 begins with colonization of the nasopharyngeal epithelium, followed by either spread within the respiratory tract or invasion of the bloodstream. The mechanisms involved in the access of bacteria from the bloodstream to the central nervous system are unknown. It is possible that epithelial cells of the choroid plexus also play an important role in the pathogenesis of the meningitis. Different interactions (adhesion, invasion and toxic effects) of S. suis serotype 2 with epithelial cell lines [LLC-PK1, PK(15), A549, HeLa and MDCK] were studied and compared to those of a human pathogen which also causes meningitis, group B Streptococcus (GBS). The results showed that S. suis serotype 2, in contrast to GBS, is able to adhere to but not to invade epithelial cells. The adhesin(s) involved seem(s) to be partially masked by the capsule and are a part of the cell wall. The haemolysin produced by S. suis serotype 2 is responsible for a toxic effect observed on epithelial cells. The results described give additional evidence that pathogenesis of the infection differs between S. suis and GBS. In particular, it is possible that suilysin-positive S. suis strains use adherence and cell injury, as opposed to direct cellular invasion, as part of a complicated multistep process which leads to bacteraemia and meningitis in pigs.

Determination of the cell adhesion specificity of Streptococcus suis with the complete set of monodeoxy analogues of globotriose

Streptococcus suis causes meningitis and other serious infections in pigs and humans, and binds to host cell globotriosylceramide. In order to determine the essential hydroxyls involved in binding, the complete set of monodeoxy derivatives of the receptor trisaccharide Gal alpha1-Gal beta1-4Glc were tested as inhibitors of bacterial hemagglutination. Removal of the 4''-, 6'', 2' or 3'-hydroxyls abolished inhibitory activity, which indicated that they were critically involved in binding. The same results were obtained using synthetic lipid-linked monodeoxy derivatives of the trisaccharides in a thin-layer overlay assay. The P(N) and P(O) subtypes of the S. suis adhesin showed similar binding patterns. The hydroxyls of the glucose moiety were not critical for binding, although the adhesin binds better to the trisaccharide Gal alpha1-4Gal beta1-4Glc than the disaccharide Gal alpha1-4Gal.

Streptococcus suis: past and present

Steptococcus suis is a Gram-positive, facultatively anaerobic coccus that has been implicated as the cause of a wide range of clinical disease syndromes in swine and other domestic animals. In swine, the disease has spread worldwide but is more prevalent in countries with intensive swine management practices. The disease syndromes caused by S. suis in swine include arthritis, meningitis, pneumonia, septicaemia, endocarditis, polyserositis, abortions and abscesses. S. suis has also been implicated in disease in humans, especially among abattoir workers and swine and pork handlers. In humans, S. suis type 2 can cause meningitis, which may result in permanent hearing loss, septicaemia, endocarditis and death. The pathogenic mechanism of S. suis is not well defined. Several virulence factors have been identified, but their roles in pathogenesis and disease have not been well elucidated. Much work is in progress on characterization of virulence factors and mechanisms, with emphasis on the control of the disease. Because of the non-availability of suitable immunoprophylaxis, control of S. suis infection has depended mainly on the use of antimicrobials.

The galactosyl-(alpha 1-4)-galactose-binding adhesin of Streptococcus suis: occurrence in strains of different hemagglutination activities and induction of opsonic antibodies

The occurrence of the galactose-(alpha 1-4)-galactose-specific adhesin in Streptococcus suis, a pig and human pathogen causing sepsis, meningitis, and other serious infections, was studied. Poly- and monoclonal anti-bodies to the purified adhesin, as well as pigeon ovomucoid, a specific probe for the adhesin activity, detected one single protein band in extracts of S. suis. The adhesin was detected in all 23 strains studied, representing pathogenic serotypes (1, 2, 4, 5, 7, 8, and nontypeable) and including several weakly hemagglutinating or nonhemagglutinating strains and phase variants. The amount of adhesin detected was not correlated with the hemagglutination activity of the intact bacteria. Extraction of cells showing no binding of pigeon ovomucoid by ultrasonic treatment resulted in extracts with pigeon ovomucoid binding activity, suggesting that the adhesin was not accessible to the probe on the intact cells. Analysis of the amount of capsular polysaccharide revealed an inverse relationship between the hemagglutination activity and expression of capsular polysaccharide, thus suggesting a factor influencing adhesin accessibility. The purified adhesin was highly immunogenic and induced in preliminary experiments bactericidal activity in mice. Thus, the adhesin, with its specific binding mechanism to host cells and a proposed pathogenic role, is widely expressed among strains of different serotypes and therefore appears to represent a novel promising candidate for the development of a vaccine against S. suis.

Relationship between haemagglutination and HeLa-cell adherence of Rhodococcus equi

In this study, 45 Rhodococcus equi isolates from animals and humans were identified by the Api Coryne system, and serologically with monospecific antisera against capsular types 1-7, with serotypes 1 and 2 predominating. Regardless of serotype, 14 out of 31 isolates from animals and one of 14 isolates from humans expressed 15-17-kD virulence-associated proteins. In hexadecane adherence studies, serotype 2 isolates generally displayed hydrophobic surfaces. In addition, isolates of serotype 1 generally haemagglutinated erythrocytes from rabbits. Neither property appeared to be related to the occurrence of the virulence-associated proteins. By contrast, the haemagglutination reaction correlated significantly with the adherence of the bacteria to HeLa cells. This adhesion might serve as additional marker of virulence among isolates of R. equi and might be useful in epidemiological studies.

Purification of a galactosyl-alpha 1-4-galactose-binding adhesin from the gram-positive meningitis-associated bacterium Streptococcus suis

Streptococcus suis causes meningitis, sepsis, and other serious infections in newborn and young pigs and in adult humans. The Gal alpha 1-4Gal-binding adhesin of S. suis was purified to homogeneity by ultrasonic treatment, fractional ammonium sulfate precipitation, and preparative polyacrylamide gel electrophoresis. Pigeon ovomucoid, a glycoprotein with Gal alpha 1-4Gal terminals, was used to detect the adhesin by blotting. The purified adhesin appeared as single band of an apparent size of 18 kDa and of a pI of 6.4; no disulfide bridges were present. The amount of adhesin as revealed by pigeon ovomucoid binding correlated with the hemagglutination activity of different S. suis strains. The purified adhesin bound to latex particles induced hemagglutination which was specifically inhibited with the same inhibitors as hemagglutination by the intact bacteria, thus demonstrating that the purified protein was the Gal alpha 1-4Gal-recognizing adhesin of S. suis. Two adhesin variants (PN and PO) with differing Gal alpha 1-4Gal binding specificity had the similar electrophoretic mobilities and the same N-terminal peptide sequences, indicating that they were closely related. This represents the first isolation of an adhesin with well-defined cell surface carbohydrate binding activity from Gram-positive bacteria associated with meningitis.

Hemagglutination properties of Enterococcus

In total, 86 enterococcal strains including representatives of most of the described species were tested for the ability to agglutinate human, sheep, and rabbit erythrocytes. Five strains did not react with any of the erythrocytes tested, and 81 (94.2%) strains agglutinated only rabbit erythrocytes. The hemagglutination titers ranged from 2 to 64. Loss of the hemagglutination activity was observed when rabbit erythrocytes were treated with trypsin or neuraminidase. Trypsin treatment of the bacterial suspensions also caused loss of the agglutination ability. On the other hand, heat treatment of bacterial suspensions increased the efficiency of the interactions, and higher titers were obtained. Assays for inhibition of hemagglutination were performed with alpha-D-fucose, alpha-D-galactose, beta-D-galactose, D-glucose, N-acetyl-galactosamine, N-acetyl-glucosamine, N-acetylneuraminic acid, N-acetylneuraminic acid-lactose, and fetuin. Only fetuin was able to inhibit the hemagglutination reactions. The results showed that hemagglutination properties are common to the different enterococcal species tested. They also suggest that enterococci possess hemagglutinins of proteic and non-proteic nature that are involved in the attachment to sialic acid-containing receptors on the surface of rabbit erythrocytes.

Enterococcus faecalis and otitis media with effusion. How to treat

Although microorganisms are cultured in only one out of 3 middle ear effusions, viable and non-viable bacteria are presumed to be responsible in part for otitis media with effusion (OME). Because of this association, antibiotics in sublethal, bacteriostatic, or bacteriocidal concentrations are frequently used as non-surgical therapy for OME. Antibiotic treatment is predicated on the assumption that microorganisms responsible for OME are the same ones which produce acute otitis media. This may not always be the case. Enterococcus faecalis (formerly known as beta-hemolytic group D Streptococcus) was isolated in pure culture from 3 middle ears of two patients with OME. The significance of the isolation of this bacteria, an enteric organism which is infrequently found in upper respiratory tracts, is its lack of susceptibility to the usually prescribed oral antibiotics. In each of the children, failure to respond to antibiotics led to tympanocentesis and culture followed by middle ear drainage with insertion of middle ear ventilating tubes. Unless intravenous antibiotics are used, surgical drainage should be the procedure of choice when E. faecalis is found in the middle ear.

Hemagglutination properties of Streptococcus suis

A total of 49 strains (23 reference strains and 26 field isolates) of Streptococcus suis were tested for their ability to agglutinate erythrocytes from different animal species. Ten different hemagglutination patterns were established. Thirty-three strains (67%) did not agglutinate any of the erythrocytes tested; sixteen strains (33%) agglutinated erythrocytes from one or more animal species. Different strains belonging to the same capsular type presented different hemagglutination patterns. No correlation was found between the tissue origin and/or the virulence (evaluated in 4-week-old mice) of different field isolates and their hemagglutination activity. Hydrophobic surface properties were also evaluated. All S. suis strains studied appeared to possess a hydrophilic cell surface. Morphologically similar fimbriae were observed on hemagglutinating as well as on nonhemagglutinating strains of S. suis. This study provides evidence that certain strains of S. suis possess hemagglutinating properties which do not appear to involve hydrophobic interactions. The possible role of fimbriae in hemagglutination remains unclear.

Ultrastructural study of surface components of Streptococcus suis

The presence of capsular material on cells of nine reference strains of Streptococcus suis representing serotypes 1 to 8 and 1/2 was determined by transmission electron microscopy after polycationic ferritin labeling, immunostabilization, or fixation with a combination of glutaraldehyde and lysine. All the cells of the reference strains examined were covered with a layer of capsular material whose thickness varied between 20 to 30 nm and 350 to 375 nm when examined by immunostabilization. Capsular material from cells exposed to homologous antiserum was usually thicker than that from polycationic ferritin-labeled cells or cells fixed with glutaraldehyde-lysine. Negative staining revealed detectable surface structures on S. suis strains. All strains carried peritichous, thin, and flexible fimbriae with a diameter of approximately 2 nm and a length of up to 250 nm. This study indicated that morphological differences of surface structure exist among S. suis reference strains.

Description of 14 new capsular types of Streptococcus suis

Fourteen new capsular types of Streptococcus suis (types 9 to 22) are described. All reference strains are morphologically and biochemically similar to types previously described. Reference strain types 9 to 13, 15, 16, and 22 were isolated from diseased pigs, whereas types 17 to 19 and 21 came from clinically healthy pigs; type 14 was isolated from a human case of meningitis, and type 20 was isolated from a diseased calf. The group T streptococcus of de Moor has been included in the typing system as type 15. Two-way cross-reactions between types 6 and 16 and a one-way cross-reaction between types 2 and 22 have been demonstrated. In addition, several cross-reactions probably not due to capsular material were detected among different types by using the coagglutination test. This test should not be used alone; weak or multiple positive reactions must be confirmed by the capsular reaction test or the capillary precipitation test.