Soluble group- and type-specific antigens from type III group B Streptococcus

Neutrophils discriminate live from dead bacteria by integrating signals initiated by Fprs and TLRs

The mechanisms whereby neutrophils respond differentially to live and dead organisms are unknown. We show here that neutrophils produce 5- to 30-fold higher levels of the Cxcl2 chemokine in response to live bacteria, compared with killed bacteria or isolated bacterial components, despite producing similar levels of Cxcl1 or pro-inflammatory cytokines. Secretion of high levels of Cxcl2, which potently activates neutrophils by an autocrine mechanism, requires three signals. The first two signals are provided by two different sets of signal peptides released by live bacteria, which selectively activate formylated peptide receptor 1 (Fpr1) and Fpr2, respectively. Signal 3 originates from Toll-like receptor activation by microbial components present in both live and killed bacteria. Mechanistically, these signaling pathways converge at the level of the p38 MAP kinase, leading to activation of the AP-1 transcription factor and to Cxcl2 induction. Collectively, our data demonstrate that the simultaneous presence of agonists for Fpr1, Fpr2, and Toll-like receptors represents a unique signature associated with viable bacteria, which is sensed by neutrophils and induces Cxcl2-dependent autocrine cell activation.

Bacterial glycobiology: rhamnose-containing cell wall polysaccharides in Gram-positive bacteria

The composition of the Gram-positive cell wall is typically described as containing peptidoglycan, proteins and essential secondary cell wall structures called teichoic acids, which comprise approximately half of the cell wall mass. The cell walls of many species within the genera Streptococcus, Enterococcus and Lactococcus contain large amounts of the sugar rhamnose, which is incorporated in cell wall-anchored polysaccharides (CWP) that possibly function as homologues of well-studied wall teichoic acids (WTA). The presence and chemical structure of many rhamnose-containing cell wall polysaccharides (RhaCWP) has sometimes been known for decades. In contrast to WTA, insight into the biosynthesis and functional role of RhaCWP has been lacking. Recent studies in human streptococcal and enterococcal pathogens have highlighted critical roles for these complex polysaccharides in bacterial cell wall architecture and pathogenesis. In this review, we provide an overview of the RhaCWP with regards to their biosynthesis, genetics and biological function in species most relevant to human health. We also briefly discuss how increased knowledge in this field can provide interesting leads for new therapeutic compounds and improve biotechnological applications.

This review summarizes new insights into the genetics and function of rhamnose-containing cell wall polysaccharides expressed by lactic acid bacteria, which includes medically important pathogens, and discusses perspectives on possible future therapeutic and biotechnological applications.

FbsC, a novel fibrinogen-binding protein, promotes Streptococcus agalactiae-host cell interactions

Streptococcus agalactiae (group B Streptococcus or GBS) is a common cause of invasive infections in newborn infants and adults. The ability of GBS to bind human fibrinogen is of crucial importance in promoting colonization and invasion of host barriers. We characterized here a novel fibrinogen-binding protein of GBS, designated FbsC (Gbs0791), which is encoded by the prototype GBS strain NEM316. FbsC, which bears two bacterial immunoglobulin-like tandem repeat domains and a C-terminal cell wall-anchoring motif (LPXTG), was found to be covalently linked to the cell wall by the housekeeping sortase A. Studies using recombinant FbsC indicated that it binds fibrinogen in a dose-dependent and saturable manner, and with moderate affinity. Expression of FbsC was detected in all clinical GBS isolates, except those belonging to the hypervirulent lineage ST17. Deletion of fbsC decreases NEM316 abilities to adhere to and invade human epithelial and endothelial cells, and to form biofilm in vitro. Notably, bacterial adhesion to fibrinogen and fibrinogen binding to bacterial cells were abolished following fbsC deletion in NEM316. Moreover, the virulence of the fbsC deletion mutant and its ability to colonize the brain were impaired in murine models of infection. Finally, immunization with recombinant FbsC significantly protected mice from lethal GBS challenge. In conclusion, FbsC is a novel fibrinogen-binding protein expressed by most GBS isolates that functions as a virulence factor by promoting invasion of epithelial and endothelial barriers. In addition, the protein has significant immunoprotective activity and may be a useful component of an anti-GBS vaccine.

Role of Toll-like receptor 13 in innate immune recognition of group B streptococci

Murine Toll-like receptor 13 (TLR13), an endosomal receptor that is not present in humans, is activated by an unmethylated motif present in the large ribosomal subunit of bacterial RNA (23S rRNA). Little is known, however, of the impact of TLR13 on antibacterial host defenses. Here we examined the role of this receptor in the context of infection induced by the model pathogen group B streptococcus (GBS). To this end, we used bacterial strains masked from TLR13 recognition by virtue of constitutive expression of the ErmC methyltransferase, which results in dimethylation of the 23S rRNA motif at a critical adenine residue. We found that TLR13-mediated rRNA recognition was required for optimal induction of tumor necrosis factor alpha and nitrous oxide in dendritic cell and macrophage cultures stimulated with heat-killed bacteria or purified bacterial RNA. However, TLR13-dependent recognition was redundant when live bacteria were used as a stimulus. Moreover, masking bacterial rRNA from TLR13 recognition did not increase the ability of GBS to avoid host defenses and replicate in vivo. In contrast, increased susceptibility to infection was observed under conditions in which signaling by all endosomal TLRs was abolished, i.e., in mice with a loss-of-function mutation in the chaperone protein UNC93B1. Our data lend support to the conclusion that TLR13 participates in GBS recognition, although blockade of the function of this receptor can be compensated for by other endosomal TLRs. Lack of selective pressure by bacterial infections might explain the evolutionary loss of TLR13 in humans. However, further studies using different bacterial species are needed to prove this hypothesis.

Analysis of the Streptococcus agalactiae exoproteome

The two-component regulatory system CovRS is the main regulator of virulence gene expression in Group B Streptococcus (GBS), the leading cause of invasive infections in neonates. In this study we analyzed by mass spectrometry the GBS extracellular protein complex (i.e. the exoproteome) of NEM316 wild-type (WT) strain and its isogenic covRS deletion mutant (ΔcovRS). A total of 53 proteins, 49 of which had classical secretion signals, were identified: 12 were released by both strains while 21 and 20 were released exclusively by WT and ΔcovRS strains, respectively. In addition to known surface proteins, we detected here unstudied cell-wall associated proteins and/or orthologs of putative virulence factors present in other pathogenic streptococci. While the functional role of these proteins remains to be elucidated, our data suggest that the analysis of the exoproteome of bacterial pathogens under different gene expression conditions may be a powerful tool for the rapid identification of novel virulence factors and vaccine candidates.

BIOLOGICAL SIGNIFICANCE

We believe that this manuscript will be of interest to Journal of Proteomics readers since the paper describes the identification of several putative virulence factors and vaccine candidates of the group B streptococcus, an important pathogen, using a simple proteomics strategy involving LC-MS analysis of culture supernatants obtained from two strains with divergent gene expression patterns. This technique provided the most comprehensive inventory of extracellular proteins obtained from a single streptococcal species thus far. The approach described has the added benefit of being easily applicable to a large number of different strains, making it ideal for the identification of conserved vaccine candidates.

Sialylation of group B streptococcal capsular polysaccharide is mediated by cpsK and is required for optimal capsule polymerization and expression

Several bacterial pathogens have evolved the means to escape immune detection by mimicking host cell surface carbohydrates that are crucial for self/non-self recognition. Sialic acid, a terminal residue on these carbohydrates, inhibits activation of the alternate pathway of complement by recruiting the immune modulating molecule factors H, I, and iC3b. Sialylation of capsular polysaccharide (CPS) is important for virulence of group B streptococci (GBS), a significant human pathogen. We previously reported that cpsK, a gene within the cps locus of type III GBS, could complement a sialyltransferase deficient lst mutant of Haemophilus ducreyi, implicating its role in sialylation of the GBS capsule. To explore the function of cpsK in GBS capsule production, we created a mutant in cpsK. Immunoblot analysis and enzyme-linked immunosorbent assay using anti-type III CPS antisera demonstrated that the mutant CPS did not contain sialic acid. This was confirmed by high-performance liquid chromatography after mild acid hydrolysis of the CPS. Although increased CPS chain length was seen for this strain, CPS production was <20% of the parental isolate. An episomal cpsK copy restored synthesis of sialo-CPS to wild-type levels. These data support our hypothesis that cpsK encodes the GBS CPS sialyltransferase and provide further evidence that lack of CPS oligosaccharide sialylation reduces the amount of CPS expressed on the cell surface. These observations also imply that one or more of the components involved in synthesis or transport of oligosaccharide repeating units requires a sialo-oligosaccharide for complete activity.

Mitogen-activated protein kinases and NF-kappa B are involved in TNF-alpha responses to group B streptococci

TNF-alpha is a mediator of lethality in experimental infections by group B streptococcus (GBS), an important human pathogen. Little is known of signal transduction pathways involved in GBS-induced TNF-alpha production. Here we investigate the role of mitogen-activated protein kinases (MAPKs) and NF-kappa B in TNF-alpha production by human monocytes stimulated with GBS or LPS, used as a positive control. Western blot analysis of cell lysates indicates that extracellular signal-regulated kinase 1/2 (ERK 1/2), p38, and c-Jun N-terminal kinase MAPKs, as well as I kappa B alpha, became phosphorylated, and hence activated, in both LPS- and GBS-stimulated monocytes. The kinetics of these phosphorylation events, as well as those of TNF-alpha production, were delayed by 30-60 min in GBS-stimulated, relative to LPS-stimulated, monocytes. Selective inhibitors of ERK 1/2 (PD98059 or U0126), p38 (SB203580), or NF-kappa B (caffeic acid phenetyl ester (CAPE)) could all significantly reduce TNF-alpha production, although none of the inhibitors used alone was able to completely prevent TNF-alpha release. However, this was completely blocked by combinations of the inhibitors, including PD98059-SB203580, PD98059-CAPE, or SB203580-CAPE combinations, in both LPS- and GBS-stimulated monocytes. In conclusion, our data indicate that the simultaneous activation of multiple pathways, including NF-kappa B, ERK 1/2, and p38 MAPKs, is required to induce maximal TNF-alpha production. Accordingly, in septic shock caused by either GBS or Gram-negative bacteria, complete inhibition of TNF-alpha release may require treatment with drugs or drug combinations capable of inhibiting multiple activation pathways.

Quantification of bacterial polysaccharides by the purpald assay: measurement of periodate-generated formaldehyde from glycol in the repeating unit

We have adapted the purpald assay for measurement of bacterial polysaccharides (PS) containing substituted and/or unsubstituted glycol (SG or UG) in residues such as glycerol, ribitol, arabinitol, furanosyl galactose, and sialic acid. For the purpald assay of UG-containing PS, 50 microL of PS samples was consecutively reacted with 50 microL of 16 mM NaIO4 for 20 min, 50 microL of 136 mM purpald reagent in 2 N NaOH for 20 min, and 50 microL of 64 mM NaIO4 for 20 min in a 96-well tissue culture plate followed by a measurement of absorbance at 550 nm with a plate reader. For SG-containing PS, conversion of SG to UG with 25 micro;L of 0.3 N NaOH, 1 h at room temperature for de-O-acetylation followed by 25 microL of 0.6 M H2SO4, 1 h at 80 degrees C for acid hydrolysis of PS precedes the periodate treatment in the purpald assay. The concentration of the samples can be calculated from the sample absorbance and the reference standard curve constructed from the reference concentrations of the same PS (well-characterized) and their corresponding absorbance values assayed in the same plate. The purpald assay provides a tool in addition to the existing ones for the measurement of glycol-containing PS. Among the usefulness of this method are the determinations of the glycerol content in the phospho-glycerol-containing PS and the SG and UG contents and structural integrity in PS and conjugate vaccines.

Human monocyte receptors involved in tumor necrosis factor responses to group B streptococcal products

Several group B streptococcal products have been previously found to stimulate human monocytes to produce tumor necrosis factor alpha. In order to identify the receptors involved in these responses, monocytes were stimulated with purified group- or type-specific carbohydrates or lipoteichoic acid in the presence of anti-receptor monoclonal antibodies, soluble CD14, or lipopolysaccharide-binding protein. Results indicate that CD14 plays an important role in tumor necrosis factor alpha responses to all of the stimuli tested. Moreover, both CD14 and complement receptor type 3 may be involved in responses to the group-antigen.

Estimation of group B streptococcus type III polysaccharide-specific antibody concentrations in human sera is antigen dependent

The presence of immunoglobulin G (IgG) antibodies against group B streptococcus (GBS) type III polysaccharide (PS) has been correlated with protection against GBS disease. The GBS type III PS is structurally similar to the pneumococcal type 14 PS, differing only in the presence of sialic acid residues. Four different preparations of GBS type III PS were evaluated for their specificity in enzyme-linked immunosorbent assay (ELISA): free PS, free PS mixed with methylated human serum albumin (mHSA), PS conjugated to biotin and PS conjugated to human serum albumin. Three groups of human sera were used to evaluate these PS preparations: sera from recipients of a GBS PS vaccine, sera from women receiving a GBS type III PS-tetanus toxoid conjugate vaccine, and sera from nonimmunized healthy women of childbearing age. Estimated antibody concentrations were different depending on the PS preparation used. Using any of the four preparations, we were able to measure </=0.05 micrograms of IgG antibody to the GBS type III PS per ml. The specificity of the assay was determined by competitive inhibition with homologous and heterologous PS. The pneumococcal type 14 PS did not inhibit binding of antibody to the native GBS type III PS in sera from adults receiving the GBS PS vaccine or in sera from nonimmunized adults (except serum G9). The pneumococcal type 14 PS inhibited 50% in sera from recipients of GBS type III conjugate vaccine and in serum G9 when GBS type III PS conjugated to biotin or to HSA was used as antigen in ELISA. These data show that free GBS type III PS or PS mixed with mHSA is a sensitive and specific antigen for ELISA and that conjugation can alter the antigenic specificity of a PS.

Decreased capacity for type-specific-antigen synthesis accounts for high prevalence of nontypeable strains of group B streptococci in Mexico

The low incidence of group B streptococcal (GBS) invasive neonatal disease in Mexico has been attributed to the low prevalence of serotype III strains, a major serotype in developed countries. In addition, nontypeable strains account for 12% of the isolates in Mexico and < 1% of the isolates in the United States. In this study, 57 GBS isolates (28 nontypeable by the Lancefield procedure) from carrier and infected neonates and women from Mexico were also examined for the presence of type-specific antigen by an enzymatic procedure using N-acetylmuramidase digestion of the cell wall to release soluble type-specific antigen. Of the 28 nontypeable strains from Mexico, 23 were typeable by the enzyme extraction procedure, with serotype III being the predominant serotype in invasive disease. These results suggest that nontypeable isolates of GBS should be further examined by the enzymatic extraction procedure to determine the presence of type-specific antigen. Furthermore, these limited results suggest that serotype III is likely a major serotype in invasive disease also in Mexico.

Soluble antigens from group B streptococci induce cytokine production in human blood cultures

Group B streptococcal antigens stimulated tumor necrosis factor alpha (TNF-alpha), interleukin-1 (IL-1), and IL-6 production in human blood cultures in a concentration- and time-dependent fashion. The minimal concentrations of type-specific polysaccharides, lipoteichoic acid, and group-specific polysaccharide required to produce these effects were, respectively, 0.01, 1, and 10 microg/ml. Cell separation experiments indicated that monocytes were the cell type mainly responsible for cytokine production. Time course studies indicated that TNF-alpha was released before the other cytokines. TNF-alpha, however, did not appear to directly induce IL-1beta, as shown by blockade experiments with anti-TNF-alpha antibodies. IL-6 levels were moderately but significantly decreased by anti-TNF-alpha. These data indicate that several products from group B streptococci are able to directly stimulate human monocytes to release TNF-alpha, IL-1beta, and IL-6. These findings may be clinically relevant, since proinflammatory cytokines can mediate pathophysiologic changes during sepsis.

Induction of tumor necrosis factor alpha by the group- and type-specific polysaccharides from type III group B streptococci

Previous studies suggested that circulating tumor necrosis factor alpha (TNF-alpha) may have a pathophysiologic role in experimental neonatal sepsis induced by group B streptococci (GBS). This study was undertaken to investigate the ability of the type III and group-specific polysaccharides of GBS to induce TNF-alpha production and TNF-alpha-dependent lethality in neonatal rats. The cytokine was detected in plasma samples by the L929 cytotoxicity assay. Intracardiac injections of either polysaccharide induced dose-dependent, transient elevations in plasma TNF-alpha levels that returned to baseline values after 5 h. The group-specific antigen induced significantly higher mean peak TNF-alpha levels than the type III antigen (125 +/- 47 versus 44 +/- 15 U/ml with 70 mg/kg of body weight). Glycogen (70 mg/kg), used as a negative control, did not induce TNF-alpha. The lipopolysaccharide-neutralizing agent polymyxin B did not decrease TNF-alpha levels induced by either polysaccharide, ruling out contamination with endotoxin as a possible cause of TNF-alpha induction. Fifty percent lethal doses of the type III and group-specific antigens given as intracardiac injections were 105 and 16 mg/kg, respectively. Salmonella endotoxin, used as a positive control, had a 50% lethal dose of 0.1 mg/kg. The lethal activities of GBS polysaccharides, as well as endotoxin, were completely prevented by pretreatment of neonatal rats with the respective specific antibodies or anti-murine TNF-alpha serum. To assess the relative importance of the type-specific substance in TNF-alpha induction by whole bacteria, two unrelated GBS transposon mutants devoid of only the type-specific capsular polysaccharide (COH1-13 and COH31-15) were employed. Each of the heat-killed unencapsulated mutants was able to produce plasma TNF-alpha level elevations or TNF-alpha-dependent lethality but was significantly less efficient in these activities than the corresponding encapsulated wild-type strain. These data suggest that the presence of type-specific material on GBS is not necessary for the stimulation of TNF-alpha production. Type III capsular polysaccharide, however, can significantly increase the ability of GBS to induce TNF-alpha. Further studies will be needed to assess the importance of TNF-alpha induction by the group- and type-specific antigens in the pathophysiology of GBS disease.

Comparison of group B streptococcal hyperimmune globulin and standard intravenously administered immune globulin in neonates

Standard intravenously administered immune globulin (IVIG) contains varying amounts of group B streptococcus (GBS) antibody. A GBS hyperimmune IVIG was produced by immunizing plasma donors. The GBS type-specific opsonic activity was > or = 90% in the hyperimmune IVIG at a 1280 dilution-1 versus at a 10 dilution-1 in standard IVIG. Suckling rat survival after GBS type-specific infection was 100% when the rats were treated with hyperimmune IVIG versus < or = 20% with standard IVIG. To evaluate the effect of this product on GBS antibody levels and clinical toxic effects, we randomly administered either GBS hyperimmune IVIG, 500, 250, or 100 mg/kg, or standard IVIG, 500 mg/kg, to 20 neonates with suspected sepsis. No adverse effects were observed. Total and subclass serum IgG levels reflected only the dose; serum GBS type-specific IgG and opsonic activity reflected both the product and dose of IVIG administered. Standard IVIG did not significantly increase serum GBS type-specific IgG, whereas hyperimmune IVIG, 500 mg/kg, produced a fourfold rise for > 6 weeks; more variable increases were observed after 250 and 100 mg/kg doses were given. Serum GBS type-specific opsonic activity correlated with serum GBS type-specific IgG levels (R2 = 0.74; p < 0.0001). Further studies of this or similar products will be necessary to determine whether GBS type-specific antibody improves the outcome of GBS-infected neonates.

Cytokine appearance and effects of anti-tumor necrosis factor alpha antibodies in a neonatal rat model of group B streptococcal infection

Cytokines are suspected of playing an important role in the pathophysiology of septic shock. This study was undertaken to determine whether tumor necrosis factor alpha (TNF-alpha) induces the production of other cytokines and mediates mortality in a neonatal rat model of sepsis caused by group B streptococci (GBS). We have measured TNF-alpha, interleukin-1 alpha (IL-1 alpha), interleukin-6 (IL-6), and gamma interferon (IFN-gamma) levels in neonatal rats infected with different strains (H738, 259, and 90) and doses (1 50% lethal dose [LD50] and 5 90% lethal doses [LD90]) of type III GBS. TNF-alpha and IL-6 were detected by the L929 cytotoxicity and the B9 proliferation assays, respectively, in serial plasma samples. IL-1 alpha and IFN-gamma were measured in spleen homogenates by enzyme-linked immunosorbent assay kits by using antibodies raised against the corresponding mouse cytokines. Plasma TNF-alpha levels significantly rose above baseline values within 12 h after intraperitoneal challenge with 5 LD90 of GBS strain H738, corresponding to 3 x 10(3) CFU. A mean peak TNF-alpha concentration of 232 +/- 124 U/ml was reached at 20 h. Peak IL-1 alpha and IL-6 levels of 766 +/- 404 U/g and 1,033 +/- 520 U/ml, respectively, were reached at 24 h after bacterial challenge. Maximal spleen concentrations of IFN-gamma (449 +/- 283 U/g) were measured at 36 h. Concentrations of TNF-alpha, but not other cytokines, remained significantly elevated at 72 h, a time when mortality approached 100%. Significant correlations were found between concentrations of each of the cytokines tested and the logs of CFU concentrations in the blood. In order to ascertain whether TNF-alpha influenced the production of other cytokines, rat pups received two injections of anti-murine TNF-alpha or normal rabbit serum at 2 h before and at 26 h after challenge with live GBS. Plasma TNF-alpha bioactivity was undetectable in anti-TNF-alpha-treated animals, while IL-6 and IFN-gamma, but not IL-1 alpha, levels were significantly reduced, compared with normal serum controls. Rat pups pretreated with anti-TNF-alpha serum and infected with 1 and 5 LD90 of strains H738 and 259 showed enhanced early (48 to 72 h) survival. However, by 96 h this protection was no longer apparent.

Intravenous immune globulin therapy for early-onset sepsis in premature neonates

Newborn infants may have IgG deficiencies that increase their susceptibility to bacterial infection. To determine whether intravenous immune globulin (IVIG) therapy improves survival rates in early-onset sepsis, we prospectively entered 753 neonates (birth weight 500 to 2000 gm, gestation less than or equal to 34 weeks, age less than or equal to 12 hours) into a multicenter, double-blind, controlled trial. Blood culture specimens were obtained and infants randomly assigned to receive 10 ml (per kilogram) intravenously of a selected IVIG (500 mg/kg) or albumin (5 mg/kg) preparation. Maternal and neonatal risk factors were not different between groups. Thirty-one babies (4.2%) had early-onset sepsis; the causative organisms were group B streptococcus (12 babies), Escherichia coli (6), and others (13). Of these 31 neonates, 7 (23%) died. Total serum IgG was higher for 7 days after IVIG therapy than after albumin treatment (p less than 0.05). During these 7 days, 5 (30%) of 17 albumin-treated and none of 14 IVIG-treated patients died (p less than 0.05). The survival rate at 56 days of age, however, was not significantly improved. Group B streptococcus type-specific IgG antibody was significantly increased after IVIG treatment and appeared to be related to the amount of IVIG specific antibody. Infusion-related adverse reactions were less frequent in patients receiving IVIG therapy (0.5%) than in those receiving albumin. The IVIG therapy in neonates with early-onset sepsis, while reducing the early mortality rate, did not significantly affect the overall survival rate. Further studies are necessary to confirm these findings and to determine more effective therapeutic regimens.

Isotype antibody response in cows to Streptococcus agalactiae group B polysaccharide-ovalbumin conjugate

Adult dairy cows were immunized with group B antigen (GBA) of Streptococcus agalactiae or GBA coupled to ovalbumin, both emulsified in incomplete Freund adjuvant, and their sera were examined by an enzyme-linked immunosorbent assay measuring bovine immunoglobulin isotypes (immunoglobulin G1 [IgG1], IgG2, and IgM) specific for GBA. All of the cows possessed naturally acquired antibodies against GBA, which implied that primary antibody responses could not be studied. At the highest dose tested (200 micrograms), free GBA elicited a slight increase in antibody titers only in the IgM isotype, to which most of the naturally acquired antibodies to GBA belonged. A second administration of antigen was not more effective. The conjugate was able to induce a strong humoral response against GBA, particularly in the IgG1 and IgG2 subisotypes, and a second injection of the conjugate induced a doubling of the peak antibody titers. Therefore, conjugation of GBA to a protein carrier markedly improved the antibody response, which showed the main characteristics of T-cell dependency. The opsonic activity of serum against an unencapsulated strain of S. agalactiae was reinforced by the immunization with the conjugate.

Specificity and Protective Activity of Murine Monoclonal Antibodies Directed Against the Capsular Polysaccharide of Type III Group B Streptococci

We have obtained 41 monoclonal antibodies directed against type III group B streptococci by immunizing Balb/c mice with formalin-killed bacteria. All of these antibodies reacted with purified type-specific carbohydrate by enzyme-linked immunosorbent assay and immunoprecipitation tests. The epitope recognized by all of these antibodies was associated with terminal sialic acid residues, as indicated by abrogation of immune reactions by treatment of the type-specific carbohydrate with neuraminidase. Two purified monoclonal antibodies (the IgM P9D8 and the IgG3 P4F12) were further characterized for their protective activity in a neonatal rat model of infection. P9D8 and P4F12 antibodies were significantly protective when administered in a dose of 0.5 and 2.5 mg/kg, respectively, at the same time as 3 x 10(5) colony forming units of type III streptococci. Protection was still observed when the antibodies were given up to 9 h after challenge. No protection was afforded against infections with type Ia/c and II streptococci. Similarly, both antibodies effectively opsonized type III, but not Ia, Ib or II bacteria, in an in vitro assay. These and similar, previously described, monoclonal antibodies may be useful, possibly after "humanization" by genetic engineering, for the therapy of neonatal group B streptococcal infections.

Directed immune globulin for the prevention or treatment of neonatal group B streptococcal infections: a review

Intravenous immune globulin (IVIG) is now used in many nurseries to prevent or treat neonatal infections. The most common cause of early-onset neonatal sepsis is the group B streptococcus (GBS). Commercially available IVIG preparations have variable levels of specific antibody directed against GBS. Therefore, to ensure high levels of anti-GBS antibody, we developed a polyvalent IVIG directed against GBS (GBS-IVIG) by immunizing plasma donors. This GBS-IVIG was superior to standard IVIG both in vitro using opsonic studies and in vivo using a lethal suckling rat model of GBS sepsis. GBS-IVIG also protected neonatal rhesus monkeys in a GBS sepsis model. Safety and pharmacokinetic studies have been completed in 20 neonates with suspected sepsis. Fifteen infants were randomized to receive 500, 250, or 100 mg/kg of GBS-IVIG and were compared with 5 infants given 500 mg/kg of standard IVIG. No adverse effects of standard IVIG or GBS-IVIG were observed. While total serum IgG and IgG subclasses reflected the dose administered, the specific GBS antibody reflected both the dose and IVIG preparation utilized. At 500 mg/kg, the GBS-specific antibody rises more than fourfold above baseline in all babies that were observed for greater than 42 days postinfusion, while standard IVIG provided a fourfold rise in less than 20% of babies for less than 1 day. These studies suggest that GBS-IVIG can effectively and reliably elevate GBS-specific antibody levels in neonates. Clinical trials are needed to evaluate the efficacy of GBS-IVIG in preventing or treating neonatal GBS infections.

Comparison of commercially available group B streptococcal latex agglutination assays

Detection of group B streptococcus (GBS) antigen in urine by latex particle agglutination (LPA) may facilitate the rapid diagnosis of GBS sepsis. We sought to compare three commercial LPA assays with specimens that were spiked with type-specific antigen, group-specific antigen, or type III organisms. There were sensitivity differences between the assays, but the Bactigen assay performed best, detecting as little as 1 ng of GBS group-specific antigen per ml in urine and as few as 10(5) CFU of GBS type III organisms per ml in urine, serum, and cerebrospinal fluid.

The alpha-L-(1----2)-trirhamnopyranoside epitope on the group-specific polysaccharide of group B streptococci

A number of epitope specificities associated with the group antigen (group B polysaccharide) of group B streptococci have been identified in a polyclonal antiserum induced in rabbits by a nonencapsulated variant strain of group B streptococci. This was achieved by using a series of oligosaccharide inhibitors, obtained by both synthetic and degradative procedures, to inhibit the binding of the group B polysaccharide to the polyclonal antiserum. While the dominant epitope expressed in the antiserum was alpha-L-Rhap(1----2)alpha-L-Rhap(1----2)alpha-L-Rhap, specificities associated with alpha-L-Rhap and alpha-L-Rhap(1----3)alpha-D-Galp(1----3)beta-D-Glcp-NAc(1----4)alp ha-L-Rhap were also identified. The dominant expression of the former epitope is consistent with its terminal location on the group antigen and also with highly branched multiantennary structure of this antigen. Antibodies specific for the alpha-L-trirhamnopyranoside epitope were purified by affinity chromatography, using the synthetic trisaccharide glucitol as the hapten. Oligosaccharide inhibition studies indicate that the specificity of these antibodies is identical to that of a murine monoclonal antibody induced by the same nonencapsulated strain of group B streptococci.

Quantitative measurement of group B streptococcal antibodies (serotypes Ia, Ib, II and III) in human cord sera by the indirect enzyme-linked immunosorbent assay

Cervical and vaginal carriage of group B streptococci (GBS) is normally associated with an appropriate immune response confining these organisms to a commensal state in this human habitat. A newly developed indirect enzyme-linked immunosorbent assay compares the antibody responses against two antigen preparations of GBS-serotypes Ia, Ib, II and III in the cord sera of cervico-vaginal GBS-carriers and non-carriers during pregnancy. Antibody responses in GBS-positive women against both antigen preparations were found to be significantly higher than in GBS-negative women (p less than 0.005). Antibody levels towards the EDTA-antigen were markedly lower than levels for the HCl-antigen thus indicating two different antibody responses.

Synthesis and immunological properties of conjugates composed of group B streptococcus type III capsular polysaccharide covalently bound to tetanus toxoid

A synthetic scheme for covalently binding group B streptococcus type III to tetanus toxoid (TT), using adipic acid dihydrazide as a spacer, is described. Type III alone or as a conjugate with TT was injected subcutaneously into laboratory mice, and the type-specific and TT antibody responses elicited by these immunogens were assayed. Type III-TT elicited significantly higher levels of type-specific antibodies after each immunization than did the type III alone. These levels were related to the dosage of the conjugate, enhanced by Freund adjuvant, and exhibited booster responses. Type III alone elicited only immunoglobulin M (IgM) antibodies in Swiss albino mice and mostly IgM and low levels of IgG antibodies of the IgG3 subclass in BALB/c mice. Type III-TT conjugates, in contrast, elicited mostly IgG antibodies in both strains of mice. IgA type III antibodies were not detected. The first two immunizations with the conjugates elicited type III antibodies in the IgG1 and in the IgG3 subclasses. Low levels of IgG2a type III antibodies were detected after a third injection of type III-TT. Conjugate-induced antibodies facilitated opsonization of group B streptococcus type III organisms and did not react with the structurally related pneumococcus type 14. TT alone or as a component of type III-TT induced mostly antibodies of the IgG class: IgG1 levels were the highest of the four subclasses. No IgA TT antibodies were detected. The conjugation procedure, therefore, enhanced the immunogenicity of and conferred T-cell dependent properties to the type III while preserving the immunogenicity of the TT component. The T-cell dependent properties of the conjugates were responsible for stimulating IgG type III antibodies which could be boosted. Evaluation of type III-TT conjugates in antibody-negative women of child-bearing age is planned.

Molecular species of R-protein antigens produced by clinical isolates of group B streptococci

Clinical isolates of group B streptococci from body fluids and mucosal surfaces were examined for production of a trypsin-resistant antigen known as R protein. R protein was extracted with 1% trypsin from cells grown in a semidefined medium. The extracts were tested by immunodiffusion in agarose with a panel of antisera for detection and precise identification of the four species of R protein described by Wilkinson. R antigen was present in 49 of 131 (37%) of the strains tested. Analysis by serotype revealed that 0 of 2 type Ia, 0 of 11 Ib, 1 of 16 (6%) Ia/c, 12 of 15 (80%) II, 0 of 20 II/c, 35 of 49 (71%) III, 0 of 6 IV, and 1 of 12 (8%) nontypeable strains produced R antigen. Production of the R protein and the trypsin-resistant or alpha component of the c protein appeared to be mutually exclusive. R antigen was more prevalent in isolates from blood (50%) than in those from mucosal sites (27%) for type II strains; no difference was seen for type III strains from these sites. Concordant results were obtained with five paired body fluid-mucosal surface isolates from individual patients and with isolates from 17 mother-baby pairs. The most frequent species of R antigen was R4 (45 of 49), followed by R1 (4 of 49). These two species of R protein were biochemically (trypsin resistant and pepsin sensitive) and immunologically identical to the R-protein antigens produced by prototype strains of groups A, B, and C streptococci.

[Isolation of group-specific polysaccharide complexes from group B streptococci by phenol-water extraction]

The group specific polysaccharide of Group B streptococci was isolated either by means of phenol-water extraction or by Lancefield extraction procedures. Two groups of rabbits were immunized with these substances to induce polyclonal antibodies. The phenol-water extract induced antisera had a significantly higher titer against B streptococci than against A-, D- and G streptococci in the agglutination reaction. The B-specific titers in rabbits immunized with phenol-water extract were significantly higher than those obtained in the rabbits immunized with Lancefield extract. In counter immunoelectrophoresis, only the antisera prepared by immunization with phenol-water extract reacted with standard antigen from group B streptococci. The serological specificity of the phenol-water extract antigen isolated from B streptococci was confirmed by counterimmunoelectrophoresis. The antigen was a heterologous fraction with a molecular mass of 8 x 10(4)-2 x 10(6) Dalton.

Adherence of group B streptococci to adult and neonatal epithelial cells mediated by lipoteichoic acid

We have investigated the role of lipoteichoic acid in mediating the adherence of different serotypes of group B streptococci to human adult and neonatal epithelial cells. Pretreatment of neonatal buccal and vaginal epithelial cells with lipoteichoic acid, but not with deacylated lipoteichoic acid, induced a marked inhibition in the adherence of all strains tested. Pretreatment of bacteria with substances known to bind lipoteichoic acid, such as monoclonal and polyclonal antipolyglycerophosphate antibodies and albumin, also resulted in adherence inhibition. Group B streptococci adhered in 6- to 10-fold-higher numbers to buccal epithelial cells from neonates older than 3 days than to those from neonates less than 1 day old. This increase in receptiveness for group B streptococci was paralleled by an increased ability of epithelial cells from older neonates to bind group B streptococcal lipoteichoic acid. These data suggest a role for the lipid portion of lipoteichoic acid in the adherence of different serotypes of group B streptococci to vaginal and neonatal epithelial cells.

Rapid detection of group B streptococcal antigen in human amniotic fluid

Infants exposed in utero to group B streptococcus (GBS)-infected human amniotic fluid (HAF) are at high risk for serious infection. Latex particle agglutination (LPA) tests are not approved for detection of GBS in HAF. Two LPA systems, Patho-Dx Strep B and Wellcogen Strep B, were used to test unfiltered sterile HAF and filtered HAF containing concentrations of GBS carbohydrate from 0.2 to 100 micrograms/ml. Four different processing techniques were used to prevent nonspecific LPA: EDTA, nitrous acid, enzyme, and nitrous acid-heat. GBS (10(2) CFU/ml) was inoculated into filtered HAF, incubated, sampled serially, processed with enzyme, and tested by LPA. Unprocessed, unfiltered HAF showed 33% nonspecific agglutination when tested by LPA. Processing of HAF removed nonspecific agglutination and improved GBS antigen detection. Without processing, LPA could not detect less than 100 micrograms of GBS carbohydrate per ml. With nitrous acid or enzyme processing, as little as 0.2 microgram/ml could be detected. Results were easier to read after enzyme processing than after nitrous acid processing. Although both LPA systems were equally efficient, testing was easier with the Patho-Dx system. After enzyme processing, LPA could detect as few as 10(4) CFU/ml when agglutination was read with a 4 X hand lens. Substances in HAF induce false-positive reactions during LPA testing. Processing removes the interference and improves the detection of GBS. LPA testing of HAF may allow earlier identification and treatment of infants at risk for serious GBS infection.

Absence of significant cellulase activity in microbial flora of the female genital tract

It has been postulated that toxic shock syndrome may be mediated by the hydrolysis of certain tampon fibers by bacteria of the female genital tract, leading to the release of glucose that would in turn serve as a substrate for the multiplication of staphylococci producing the toxic shock marker protein (TSST-1). We sought cellulolytic organisms among microorganisms isolated from the female genital tract throughout the menstrual cycle. A total of 288 aerobic and facultative vaginal isolates from 13 healthy female volunteers, aged 18 to 25, and 57 anaerobes from the same sources were screened for cellulase activity. No evidence of production of glucose or degradation of cellulose was found; hence, none of the strains could be described as cellulolytic. A total of 44 organisms (12.7%) showed weak endoglucanase activity as evidenced by minimal changes in the viscosity of the cellulose substrate, but this activity was not reproducible in all of the strains and was inconstantly observed on repeated examination. Five strains of Staphylococcus aureus isolated from cases of toxic shock syndrome also showed no cellulase activity. Cellulase activity does not appear to be a frequent or regular feature of the microflora of the human female genital tract.

The type-specific polysaccharide and the R protein antigens of the L-phase from a group B, type III Streptococcus

The type-specific polysaccharide and the R protein antigens from filtered culture supernatants of the bacterial phase and L-phase of the group B, type III streptococcal strain 76-043 were studied by several immunological methods. In the L-phase of growth, the two antigens were separate and distinct molecules which were found principally in the culture supernatant even on the 254th serial subculture in the cell-wall-defective state. Only trace amounts of these antigens were detected in extracts of L-phase cells. The type III polysaccharide antigens in the supernatant of cultures of the parent bacterium and the L-phase gave reactions of identity in immunodiffusion. Precipitin bands obtained by immunoelectrophoresis (IEP) revealed that the type-specific antigen of the bacterial phase of growth migrated toward the anode, whereas that of the L-phase remained near the antigen well. The R protein antigen in the L-phase supernatant was immunologically identical to the R protein of the supernatant and 1% trypsin-extracted antigens from whole cells of the parent bacterial strain, and other groups A, B and C streptococcal strains sharing a common R antigen. Immunologically, the R antigen appeared to be the species R4. The R protein of the L-phase and bacterial phase cultures was resistant to 5% trypsin but sensitive to 0.5% pepsin at 37 degrees C/2hr. Antiserum prepared in rabbits against L-phase cells contained an antibody reactive with the R protein antigens of the bacterial and L-phase cultures. The soluble, naturally released type III and R protein streptococcal antigens of the L-phase of growth permitted immunological confirmation of its bacterial origin.

Immunoglobulin G and M composition of naturally occurring antibody to type III group B streptococci

Human sera were examined by an enzyme-linked immunosorbent assay for immunoglobulin G (IgG) and IgM antibodies to purified type III polysaccharide of group B streptococci. The antigen-binding capacity of a reference human serum was determined by a radioimmunoassay, and the total antibody content was determined by quantitative precipitation. The serum was then depleted of IgM and IgA to determine the effect on the antigen-binding capacity. Duplicate samples of 81 sera were tested by the enzyme-linked assay in comparison with reference standard serum. Although levels of IgG antibody were greater in subjects who had carried type III streptococci during pregnancy, concentrations of this antibody were generally low. Only 2 of 28 sera (7%) from parturient subjects and 7 of 25 sera (28%) from adult volunteers contained greater than or equal to 1 microgram of IgG antibody per ml; the mean levels were 0.13 and 0.53 micrograms/ml, respectively. In contrast, 19 of 28 maternal sera (68%) and 22 of 25 (88%) volunteer adult sera contained greater than or equal to 1 microgram/ml of IgM antibody; mean levels were 1.33 and 1.54 micrograms/ml, respectively. The cord serum levels of IgG antibody were almost identical to maternal serum concentrations, whereas IgM antibody was essentially undetected.

Interaction of group B streptococcal type-specific polysaccharides with wheat germ agglutinin and other lectins

The group B streptococci (GBS) are known to have type-specific polysaccharides rich in N-acetylneuraminic acid end groups, which are thought to be important immunological determinants. Wheat germ agglutinin (WGA) has affinity for N-acetylneuraminic acid as well as N-acetylglucosamine, and readily precipitates the type but not the group polysaccharide. A WGA-Sepharose affinity column was used to isolate complete type polysaccharides of representative strains of the 4 major GBS types. WGA, other lectins, and rabbit antisera were then used to characterize the products of various extraction procedures and chemical degradations, including mild acid hydrolysis and treatment with neuraminidase. Results of lectin binding studies were consistent with proposed chemical structures of types Ia, Ib and II. Differences were noted, however, between the cross-reactive antigens of pneumococcus type 14 and the desialated GBS type III polysaccharide. Although structurally similar, indirect evidence from lectin binding studies suggest that these antigens may not be identical.

Type-specific capsular antigen is associated with virulence in late-onset group B Streptococcal type III disease

Strain differences have been postulated to explain the observation that group B Streptococcus type III (GBS III) late-onset disease occurs in only a fraction of colonized infants. To determine the distribution of type-specific polysaccharide antigen (Ag) in GBS III, Ag was measured by rocket immunoelectrophoresis in both supernatant fluids and EDTA extracts and by radial immunodiffusion in multiple HCl extracts of the pellet from cultures of 10 strains of GBS III. Capsular Ag was defined as the sum of Ag in EDTA extracts + Ag in multiple HCl extracts. Both Ag in EDTA extracts and Ag in supernatant fluids correlated with capsular Ag (r = 0.94). GBS III strains were obtained from the blood of 19 infants with late-onset sepsis, from the cerebrospinal fluid or blood of 22 infants with late-onset meningitis, and from mucosal surfaces of both 18 infants and 12 mothers of infants with low levels of type-specific antibody and asymptomatic colonization. Mean values of Ag in supernatant fluids in strains from infants with late-onset sepsis (1.50 +/- 0.08 micrograms/ml) and late-onset meningitis (1.67 +/- 0.09 micrograms/ml) were significantly greater than those in asymptomatic colonization strains (1.14 +/- 0.05 micrograms/ml; P less than 0.001). The number of organisms required for a 50% lethal dose in the chick embryo, determined in 29 strains, was inversely related to Ag in supernatant fluids (r = -0.60). The demonstration that the quantity of capsular Ag produced by GBS III strains is related to their virulence in chick embryos and to their invasiveness in susceptible infants supports the hypothesis that Ag is a virulence factor in humans.

Isolation and characterization of type III group B streptococcal mutants defective in biosynthesis of the type-specific antigen

Four classes of mutants of type III group B streptococcus were isolated by serial subculture of the wild-type strain in the presence of type III-specific rabbit antiserum. Class I mutants no longer synthesized sialic acid but still elaborated the core antigen. Class II mutants maintained the ability to synthesize sialic acid but could not attach it to the core antigen. Class III mutants did not produce the core antigen but still synthesized intracellular sialic acid. Class IV mutants synthesized the complete antigen; however, only approximately 4% of the antigen synthesized was found associated with the cell wall peptidoglycan (in the wild-type strain greater than 85% of the antigen synthesized is covalently attached to the cell wall peptidoglycan), whereas greater than 90% of the antigen was secreted into the growth medium. Production of other components (CAMP factor, group B antigen, beta-hemolysin, neuraminidase) by these mutants appeared similar to those of the wild-type strain. Mouse lethality studies of these strains indicated that all four classes have greater than 3 log10-higher 50% lethal dose values than that of the wild-type strain. To understand the basis for this variation, the invasive ability of the wild-type strain and the sialic acid-deficient mutant strain M-10 (class I) was examined. Mice received 10(5) CFU of each organism; they were then sacrificed at various times postinoculation, and viable group B streptococci from different organs were enumerated. Mice were able to clear M-10 more efficiently, with greater than 80% of M-10 cells being phagocytized by macrophages within 1 h, whereas the wild-type strain was able to evade phagocytic killing and disseminate to other tissues. These data, therefore, strongly indicate that the sialic acid moiety greatly enhances the virulence of the type III antigen. In addition, the level of cell-associated type-specific antigen appears to contribute significantly to the pathogenicity of the organism.

Isolation, chemical composition, and molecular size of extracellular type II and type Ia polysaccharides of group B streptococci

Polysaccharides carrying the type II- and type Ia-specific determinants of Lancefield group B streptococci were isolated and purified by anion-exchange chromatography and gel filtration from the supernatant culture medium after growth of strain 18RS21/67/1 (type II) and strain DS/1204/78 (type Ia), respectively. The average molecular weights of these polysaccharides were 97,000 (type II) and 94,000 (type Ia), as determined by reducing end group analyses. These molecular weights were in reasonably good agreement with molecular weights determined by gel filtration at high ionic strength on calibrated columns. The polysaccharides did not cross-react with antisera specific for the other type-specific determinants or with group B-specific antisera. Their content of galactose, glucose, glucosamine, and neuraminic acid (the last two calculated as N-acetyl derivatives) accounted for over 96% of their dry weight. The two polysaccharides differed from each other (and from type III polysaccharide) in their relative content of these monosaccharides. The molar ratios of galactose, glucose, and neuraminic acid to glucosamine were 3.3:2.3:1.35:1.0 for the type II polysaccharide and 2.0:0.8:1.4:1.0 for the type Ia polysaccharides. The results obtained indicate that these extracellular type II and Ia polysaccharides contain larger amounts of neuraminic acid than can be accounted for by previously proposed structures of their repeating units.

Immunochemical analysis and immunogenicity of the type II group B streptococcal capsular polysaccharide

The relationship between group B streptococcal (GBS) type-specific antisera and the type II-specific polysaccharide is evaluated from a structural and immunologic viewpoint. Although all GBS type-specific polysaccharides are composed of the same monosaccharides, the type II antigen is more complex structurally and contains these sugars in a molar ratio different from the other antigens. Type II polysaccharide has two side chains. One contains only sialic acid and is less susceptible to acid cleavage than sialic acid residues found on types III, Ia, and Ib polysaccharides. The other side chain is composed of galactose as the only sugar. Immunochemical studies demonstrate that the type II polysaccharide has several immunodeterminants. One of these determinants is likely to be the side-chain galactose, while sialic acid appears to comprise part of another immunodeterminant, more complex than sialic acid alone. A series of cross-reactions is demonstrated between the type II native antigen and antisera to serotypes Ia, III, and Ib by a sensitive radioactive antigen-binding assay, which account for additional, complex immunodeterminants. The strongest of these cross-reactions is with type Ia antiserum and the weakest with Ib antiserum. Since Ia and Ib polysaccharides differ in only one linkage, these findings suggest that the trisaccharide beta D-N-acetyl-glucosamine-p(1 leads to 3) beta D-galactose-p(1 leads to 4) beta D-glucose-p [[beta D-GlcNAcp(1 leads to 3) beta D-Galp(1 leads to 4)beta D-Glcap]] is the likely common site responsible for the interaction of the type II native polysaccharide and type Ia antiserum. Another cross-reaction is observed between type III antiserum and type II native antigen. Inhibition studies indicate that the most likely cross-reactive determinant in this case is [beta D-Galp(1 leads to 4)beta D-GlcNAcp]. Type II polysaccharide has been utilized in a human vaccine trial to test safety and immunogenicity. The polysaccharide is highly immunogenic, inducing an antibody response in 95% of recipients, and nontoxic, with side-effects confined to minimal local reactions. Despite the cross-reactions observed between type-specific antigens and antibody prepared by immunization of rabbits with whole bacteria, which suggest shared immunodeterminants, similar cross-reactions were not detected in human sera after immunization with purified type II polysaccharide.

Association of bacterial carbohydrate-specific cold agglutinin antibody production with immunization by group C, group B type III, and Streptococcus pneumoniae type XIV streptococcal vaccines

Rabbits immunized with group B type III, group C, and Streptococcus pneumoniae type XIV streptococcal vaccines developed autoantibodies reactive with autologous and isologous erythrocytes and human O-positive erythrocytes at reduced temperatures. The cold agglutinin antibodies were present in both the immunoglobulin M (IgM) and IgG fractions of group C streptococcal antiserum and in the IgM fraction of group B type III and S. pneumoniae type XIV antisera. BALB/c, CF1, and local strains of mice immunized with group B type III and S. pneumoniae type XIV streptococcal vaccines also produced a cold agglutinin antibody reactive with rabbit and human erythrocytes. The cold agglutinin antibodies were reactive with saccharide compounds representative of the determinants present on the individual bacterial carbohydrate structures, individual vaccine preparations, and isolated polysaccharides. The group C antibodies in rabbits were reactive with sugar ligands in the following order: N-acetylgalactosamine greater than melibiose greater than lactose greater than galactose greater than glucose. Group B type III and S. pneumoniae type XIV cold agglutinin antibodies in rabbit antisera, however, displayed reactivities different from group C antibodies and from each other. Group B type III antibodies reacted with galactose greater than lactose greater than N-acetylgalactosamine greater than glucose greater than rhamnose; S. pneumoniae type XIV antibodies reacted with lactose greater than melibiose greater than galactose greater than glucose greater than N-acetylgalactosamine. The same relative ligand specificity was observed for the cold agglutinin antibodies in S. pneumoniae type XIV mouse antisera. The cold agglutinin antibodies in group B type III and S. pneumoniae type XIV antiserum reacted with erythrocytes at higher temperatures (up to 31 degrees C) than did group C antibodies (up to 14 degrees C). In addition, S. pneumoniae type XIV antibodies did not discriminate between I- or i-bearing human erythrocytes to a significant extent. The results obtained provide substantial evidence that autoreactive cold agglutinin antibodies produced by immunization with these vaccines represent subpopulations of bacterial carbohydrate-specific antibodies that cross-react with mammalian carbohydrate structures.

Detection of group B streptococcal antigens in amniotic fluid of rhesus monkeys

To simulate group B streptococci (GBS) amniotic fluid infections common in humans and to examine bacterial growth and the appearance of GBS antigens in vivo, GBS were injected into the amniotic cavity of 19 near-term rhesus monkeys. Transabdominal aspirates of amniotic fluid were obtained before bacterial challenge, after 2 and 6 h, and during cesarean section delivery (24 h). Each fluid was quantitatively cultured for GBS. Specimens of amniotic fluid and gastric aspirate from each infant were tested for the presence of GBS antigens with a commercial latex particle agglutination test (Wellcogen Strep B; Wellcome Diagnostics, Dartford, England). To eliminate nonspecific latex particle agglutination reactivity, presumably caused by proteins, a processing procedure was required. Despite active proliferation of bacteria, only 12% of the 2-h amniotic specimens were latex particle agglutination positive. In contrast, 94% of th3 6-h and 100% of the 24-h specimens had detectable antigens, as did 89% of the gastric fluid specimens aspirated from the 19 newborns. Latex particle agglutination tests, after proper processing, will readily detect GBS antigens in amniotic or gastric aspirate fluid from experimentally infected rhesus monkeys.

Biosynthesis of cell wall peptidoglycan and polysaccharide antigens by protoplasts of type III group B Streptococcus

The formation of a nascent peptidoglycan-group-specific antigen of type III group B Streptococcus at the cell membrane level was demonstrated with an M-1 mutanolysin-prepared protoplast system. Protoplasts of group B streptococci in suitably stabilized medium (20% sucrose) readily incorporated [3H]acetate into cell surface macromolecules. Four major polysaccharides were isolated from the protoplast cultural supernatant fluid: the peptidoglycan group-specific antigen polymer, the group B-specific antigen, and the low-molecular-weight and high-molecular-weight forms of the type III polysaccharide antigen. Biosynthesis of all four polymers was not affected by the action of chloramphenicol, indicating protein synthesis was not required for the production of polysaccharide in this system. However, all but the low-molecular-weight type III antigen were inhibited by the action of bacitracin, suggesting that three of the polymers share a common synthesis-assembly site in the membrane. Attachment of the high-molecular-weight antigen to the nascent peptidoglycan-group B antigen complex did not occur in the protoplast system, suggesting that a more complex cell wall matrix may be necessary before linkage of the high-molecular-weight antigen takes place.

Quantitation of in vitro opsonic activity of human antibody induced by a vaccine consisting of the type III-specific polysaccharide of group B streptococcus

Human antibody, induced by a vaccine consisting of undegraded and highly purified extracellular type III-specific polysaccharide of group B streptococcus, was shown to increase the rate of phagocyte-mediated killing of bacteria of the homologous type. The bactericidal effect was mediated by type III-specific antibody and was complement dependent. An assay which permitted quantitation of "opsonic activity" was developed. In this assay, loss of CFUs occurred at a constant rate, and the rate constant was used as a measure of opsonic activity of antisera. A linear relationship between type III-specific antibody concentration (40 to 500 ng/ml) and the rate constant of killing was observed. When sets of immune sera were tested, some sera reacted anomalously, mediating significantly higher or lower rates than expected on the basis of their antibody content. Since type III-specific antibody in immune sera was found almost exclusively in the immunoglobulin G class, we hypothesize that differences in immunoglobulin G subclass distribution of specific antibody may have been the source of this variation.

Type-specific protection of neonatal rats from lethal group B streptococcal infection by immune sera obtained from human volunteers vaccinated with type III-specific polysaccharide

Sera obtained from human volunteers at 6 weeks after vaccination with highly purified type III polysaccharide antigen prepared from a group B Streptococcus, strain M732, were found to protect neonatal rats from otherwise lethal infection by the homologous strain. The specific antibody content of the sera, expressed in micrograms of antibody protein per milliliter, was determined by an enzyme-linked immunosorbent assay in conjunction with quantitative precipitin analysis. For two sera studied in detail, the protective dose of antibody for 50% of the animals was 0.4 micrograms. Immune serum obtained from a volunteer who received type II polysaccharide vaccine was not protective against type III infection. Absorption of anti-type III serum by quantitative precipitation of antibodies with type III polysaccharide completely removed the passive protective activity of the serum. The results show that antibodies induced in humans by purified type II polysaccharide give serotype-specific protection in an animal model of neonatal infection.

Immunospecificity and quantitation of an enzyme-linked immunosorbent assay for group B streptococcal antibody

Type-specific antigen was purified from the supernatant of type III group B streptococcal cultures, tyrosylated, and bound to microtiter wells for an enzyme-linked immunosorbent assay. The immunological specificity of the antigen and the assay was shown by (i) reaction only with homologous unabsorbed rabbit sera and (ii) inhibition after incubation of human serum with homologous but not heterologous purified antigen. The assay was quantitated by relating optical density readings to absolute amounts of human immunoglobulin G bound to the microtiter wells.

Monoclonal antibody to streptococcal group B carbohydrate: applications in latex agglutination and immunoprecipitin assays

Two monoclonal mouse antibodies with specificities for group B streptococcal capsular antigens were evaluated in assays for the identification of group B streptococci (GBS). One of these antibodies (A9) was shown to precipitate group B carbohydrate antigen in reactions with both purified group B antigen and antigen present in autoclave or enzyme extracts of GBS. A9 antibody was also specific for group B antigen in gel diffusion reactions with extracts of Lancefield group A, B, C, D, F, and G streptococci and was a highly sensitive reagent in detecting soluble group B antigen by counterimmunoelectrophoresis. Antigen extracted from all five serotypes of GBS was shown to be precipitated by A9 antibody. A second monoclonal antibody (C8) was reactive with intact GBS but did not precipitate soluble antigen in bacterial extracts. In contrast with what has been shown for polyclonal rabbit anti-group B antiserum, neither antibody was significantly inhibited in binding or precipitation assays by high concentrations of free rhamnose or other monosaccharides of carbohydrates found in group B antigen. Rhamnose, the most abundant carbohydrate of the group B antigen, does not appear therefore to be an immunodominant determinant in the binding of A9 or C8 antibody. The epitopes of both monoclonal antibodies are exposed on the surface of live as well as heat-fixed GBS cells. A9 antibody-coated latex particles were compared with a commercially available polyclonal latex agglutination reagent and shown to be equally sensitive and specific in the detection of soluble group B antigen in urine and cerebrospinal fluid from patients with GBS infections. Because of its uniformity and defined antigen specificity, which includes reactivity with all five serotypes of GBS, A9 antibody offers the potential of an improved immunodiagnostic reagent for the identification of GBS.

Group B, type III streptococcal cell wall: composition and structural aspects revealed through endo-N-acetylmuramidase-catalyzed hydrolysis

Cell walls from a group B, type III streptococcus strain were prepared, purified by extraction with sodium dodecyl sulfate, and solubilized by the M-1 fraction of mutanolysin, an endo-N-acetylmuramidase obtained from Streptomyces globisporus. The lysate was resolved into three fractions by ion-exchange chromatography: a fraction containing peptidoglycan (PG) fragments, free of neutral and acidic sugars and of phosphate; a complex of PG fragments and group B-specific polysaccharide; and a complex of PG fragments and group B-specific polysaccharide and type III-specific polysaccharide. The PG-polysaccharide complexes were large and heterogeneous in molecular size. When subjected to base-catalyzed beta-elimination, both complexes were disintegrated, and polysaccharides and low-molecular-weight PG fragments could then be separated by gel filtration. The low-molecular-weight PG fragment-containing fraction contained muramic acid, glucosamine, alanine, lysine, glutamic acid, and serine in molar ratios (to lysine) of 0.92:0.98:3.01:1.00:1.00:0.05. Wall-derived, purified group polysaccharide contained rhamnose, galactose, glucosamine, and phosphorus in molar ratios (to galactose) of 5.03:1.00:1.00:1.05. It also contained an unidentified sugar. Wall-derived, purified type III polysaccharide contained galactose, glucosamine, glucose, and N-acetylneuraminic acid in molar ratios (to glucose) of 1.94:0.85:1.00:1.39. On a dry-weight basis, the whole wall lysate contained 19.8 and 20.6% of group and type polysaccharide, respectively. Neither glycerol nor ribitol was found, and all of the cell wall phosphorus was accounted for as polysaccharide, indicating the absence of a wall teichoic acid.

Correlation between the production of extracellular substances by type III group B streptococcal strains and virulence in a mouse model

Twelve strains of serotype III group B streptococci (8 isolated from cases of neonatal disease, 3 isolated from asymptomatically colonized infants, and 1 laboratory reference strain) were examined for the vitro production of three potential extracellular virulence products: type-specific antigen, neuraminidase, and protease. In addition, virulence in a mouse model, expressed as 50% lethal dose, was determined for the 12 strains to determine whether a relationship existed between the production of any of the three extracellular products and virulence. Only production of extracellular type-specific antigen showed a correlation with virulence in the mouse model. The high producers of extracellular type-specific antigen were an average of 166-fold more virulent for mice than low producers of the same component. There was no correlation between virulence and either neuraminidase or protease production, nor was there a correlation between either of these two extracellular products and the levels of extracellular type-specific antigen. When levels of group B streptococci of each type (a high and low producer of extracellular type-specific antigen) in organs of infected mice were examined, comparable levels of organisms were found in the brain, spleen, and lungs of mice near death regardless of the initial inoculum. However, the high producer of extracellular type-specific antigen caused death in mice with a 2 to 3 log lower inoculum than the low producer, suggesting that these strains may be more invasive.

Factors influencing release of type III antigens by group B streptococci

The release of serotype III group B streptococcal polysaccharides into the supernatant fluid was examined under a variety of physiological conditions. Release of both high- and low-molecular-weight type III antigens was fairly constant throughout exponential growth, but increased markedly upon entering the stationary phase of growth. Increased glucose and decreased phosphate concentrations both caused a large increase in release of antigens. Inhibition of protein synthesis in exponentially growing cells by chloramphenicol (10 micrograms/ml) caused a condition of unbalanced growth in which antigen release was increased greatly over control values. Strain variability in antigen release was also observed. Strains which are known to be high neuraminidase producers released elevated levels of both low- and high-molecular-weight type III antigens. Non-neuraminidase-producing strains released considerably less high-molecular-weight antigen, but similar levels of the low-molecular-weight antigen compared with the high neuraminidase producers. Strain D136C, a type III non-neuraminidase producer, released negligible quantities of the high-molecular-weight antigen in the supernatant fluid. These results indicate that both the physiological environment and the type III strain are important in determining the quantity of type-specific antigen released into the culture fluid.

Extracellular antigens of serotype III group B streptococci

Two sialic acid-containing type III group B streptococcal antigens were obtained from a supernatant growth medium, purified by anion exchange or gel filtration, and found to be free of group B reactivity. Quantitation of the high-molecular-weight extracellular type III antigen indicated that approximately 20-fold more antigen was recoverable from the growth medium than could be obtained by neutral buffer extraction of whole cells.

Conservation of cell wall peptidoglycan by strains of Streptococcus mutans and Streptococcus sanguis

Turnover of the cell wall peptidoglycan fraction of six different strains of Streptococcus mutans and eight different strains of Streptococcus sanguis was examined. Cells were grown in the presence of [3H]lysine and [14C]leucine for at least eight generations and then chased in growth medium lacking the two labels. At intervals during the chase, samples of cultures were removed, and the amounts of the two labeled precursors remaining in the peptidoglycan and protein fractions were quantitated. Similar experiments were done in which the pulse-labeling technique was used. In addition, cells were labeled in the presence of tetracycline or penicillin, chased with growth medium containing no inhibitor, and assayed at intervals during the chase for the amount of [3H]lysine present in peptidoglycan fractions. Studies of cultures of S. mutans strains FA-1, OMZ-61, OMZ-176, 6715, GS-5, and Ingbritt and of S. sanguis strains 10558, M-5, Wicky, DL-101, DL-1, 71X26, and 71X48 maintained in the exponential phase of growth in a chemically defined medium failed to show evidence of loss of insoluble peptidoglycan via turnover. Similarly, for the strains of S. mutans, insoluble peptidoglycan assembled during 2 h of benzylpenicillin or tetracycline treatment was also conserved during recovery from growth inhibition.