Immunization of pregnant women with a polysaccharide vaccine of group B streptococcus

Immunization of pregnant women with a polysaccharide vaccine of group B streptococcus is a promising strategy for the prevention of perinatal infections caused by group B streptococci. To explore the feasibility of this strategy, we vaccinated 40 pregnant women at a mean gestation of 31 weeks with a single 50-microgram dose of the Type III capsular polysaccharide of group B streptococcus. The only adverse effect detected was a mild local reaction in nine women (22 percent). Of the 35 women with low or unprotective antibody levels before immunization (less than 2 micrograms per milliliter), 20 (57 percent) responded to the vaccine. The geometric mean antibody level rose from 1.3 to 7.1 micrograms per milliliter four weeks after vaccination (P less than 0.02), and these levels persisted at delivery and three months post partum. Sixty-two percent of the vaccine-induced immunoglobulin in the mothers was IgG, which readily crosses the placenta. Infant antibody levels in cord serum correlated directly with maternal antibody levels at delivery (r = 0.913, P less than 0.001). Of the 25 infants born to women who responded to the vaccine, 80 percent continued to have protective levels of antibody at one month of age and 64 percent had protective levels at three months. Serum samples from infants with greater than or equal to 2 micrograms of antibody to Type III group B streptococcus per milliliter uniformly promoted efficient opsonization, phagocytosis, and bacterial killing in vitro of Type III strains. This effect could be mediated exclusively by the alternative complement pathway. Although this vaccine with an overall response rate of 63 percent is not optimally immunogenic, we conclude that maternal immunization is feasible and can provide passive immunity against systemic infection with Type III group B streptococcus in the majority of newborns. Larger trials with better vaccines will be required to evaluate the safety and clinical effectiveness of this strategy.     

Preparation and characterization of monoclonal antibodies to group-specific antigenic determinant of group a streptococcus polysaccharide

Group A streptococcus polysaccharide contains at least two different group-specific determinants including N-acetyl-β-D-glucosamine (more important) and rhamnose. Monoclonal antibodies to group-specific determinants of group A streptococcus polysaccharide do not react with tissue antigens. Cross reactions with tissues were detected in tests with monoclonal antibodies to rhamnose-enriched epitopes of group A streptococcus polysaccharide. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 128, No. 10, pp. 433–436, October, 1999     

Shr is a broad-spectrum surface receptor that contributes to adherence and virulence in group A streptococcus

Group A streptococcus (GAS) is a common hemolytic pathogen that produces a range of suppurative infections and autoimmune sequelae in humans. Shr is an exported protein in GAS, which binds in vitro to hemoglobin, myoglobin, and the hemoglobin-haptoglobin complex. We previously reported that Shr is found in association with whole GAS cells and in culture supernatant. Here, we demonstrate that cell-associated Shr could not be released from the bacteria by the muralytic enzyme mutanolysin and was instead localized to the membrane. Shr was available, however, on the exterior of GAS, exposed to the extracellular environment. In vitro binding and competition assays demonstrated that in addition to hemoprotein binding, purified Shr specifically interacts with immobilized fibronectin and laminin. The absence of typical fibronectin-binding motifs indicates that a new protein pattern is involved in the binding of Shr to the extracellular matrix. Recombinant Lactococcus lactis cells expressing Shr on the bacterial surface gained the ability to bind to immobilized fibronectin, suggesting that Shr can function as an adhesin. The inactivation of shr resulted in a 40% reduction in the attachment to human epithelial cells in comparison to the parent strain. GAS infection elicited a high titer of Shr antibodies in sera from convalescent mice, demonstrating that Shr is expressed in vivo. The shr mutant was attenuated for virulence in an intramuscular zebrafish model system. In summary, this study identifies Shr as being a new microbial surface component recognizing adhesive matrix molecules in GAS that mediates attachment to epithelial cells and contributes to the infection process.     

Role of the specific determinant of group A streptococcus polysaccharide in inhibition of T-suppressor activity

Group A streptococcus polysaccharide is found to inhibit the activity of ConA-stimulated T suppressors. A-variant streptococcus polysaccharide, representing an L-rhamnose homopolymer which is identical to the rhamnose carcass of group A streptococcus polysaccharide, does not possess such an effect. The effect of group A streptococcus polysaccharide on the activity of T suppressors is considered to be associated with its determinant including N-acetylglucosamine as an obligatory component. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 119, N ^o 2, pp. 201–203, February, 1995 Presented by S. V. Prozorovskii, Member of the Russian Academy of Medical Sciences     

Immunoglobulin receptors of group a streptococcus

The use of the gel precipitation test showed that adsorption of preparations of human IgG, the Fc fragments isolated from them, and of preparations of rabbit IgG with cultures of group A streptococcus inhibits the reaction of these preparations with antiglobulin sera. No inhibition of reactions of F(ab')₂ fragments took place as a result of their adsorption by the same cultures. The results confirm that certain strains of group A streptoccocus contain immunoglobulin receptors (Ig receptors), capable of reacting with Fc sites of human and rabbit IgG. The Ig receptors were shown to be destroyed by pepsin. No Ig receptors could be found by the use of this method in hydrochloric acid extracts obtained from streptococci containing these receptors. The method used in the investigation is suitable for detecting the presence of Ig receptors in streptococcal cultures.Laboratory of Streptococcal Infections, N. F. Gamaleya Institute of Epidemiology and Microbiology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR P. A. Vershilova.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 88, No. 9, pp. 319–322, September, 1979.     

Pyopericardium due to group D streptococcus

Beta-hemolytic Enterococcus faecalis was isolated from the pericardial fluid obtained from a patient with pyopericardium. The patient was immunocompetent and had mild pleural effusion. He was treated with parenteral co-amoxiclav and amikacin, had underwent pericardiectomy with repeated pericardial aspiration, and recovered completely. To our knowledge, this is the first report of pyopericardium due to E. faecalis .     

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.     

Opsonin system of the group B streptococcus

The opsonization by polymorphonuclear leukocytes of group B streptococcal serotypes associated with neonatal sepsis and delayed meningitis was studied. A specific BIa opsonizing antibody (not related to the antipolysaccharide typing antibody) was present in only 10% of the population tested. Serotype BIa was not opsonized in the absence of this specific antibody. BIa antibody specificity was demonstrated by macroagglutination and absorption with BIa streptococci and extracts, but not by gel diffusion. The binding of complement by the BIa opsonin increased the mean phagocytic activity by 60%; complement was manifested via the classic and/or alternate C3-related pathway, but seldom by both concurrently. Serotypes BIb, BIc, BII, and BIII were naturally and nonspecifically opsonized in 95% of the human and baboon sera or plasma tested. Although similar levels of opsonization were present in hyperimmune rabbit sera, heat inactivation and homologous bacterial absorption did not reduce the level of phagocytic activity in the rabbit, human, or primate groups studied. These immunological studies confirmed previous findings that serotype BIa presents a serious hazard for neonatal sepsis, with a nearly 100% mortality. Exclusive isolation of BIII in delayed meningitis suggests that ingestion and subsequent killing by polymorphonuclear leukocytes of type III may differ from the other serotypes.     

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.     

Penicillin-binding protein 1a promotes resistance of group B streptococcus to antimicrobial peptides

Evasion of host immune defenses is critical for the progression of invasive infections caused by the leading neonatal pathogen, group B streptococcus (GBS). Upon characterizing the factors required for virulence in a neonatal rat sepsis model, we found that a surface-associated penicillin-binding protein (PBP1a), encoded by ponA, played an essential role in resistance of GBS to phagocytic clearance. In order to elucidate how PBP1a promotes resistance to innate immunity, we compared the susceptibility of wild-type GBS and an isogenic ponA mutant to the bactericidal components of human neutrophils. The isogenic strains were found to be equally capable of blocking complement activation on the bacterial surface and equally associated with phagocytes and susceptible to oxidative killing. In contrast, the ponA mutant was significantly more susceptible to killing by cationic antimicrobial peptides (AMPs) of the cathelicidin and defensin families, which are now recognized as integral components of innate host defense against invasive bacterial infection. These observations may help explain the sensitivity to phagocytic killing and attenuated virulence of the ponA mutant. This novel function for PBP1a in promoting resistance of GBS to AMP did not involve an alteration in bacterial surface charge or peptidoglycan cross-linking. While the peptidoglycan polymerization and cross-linking activity of PBPs are essential for bacterial survival, our study is the first to identify a role for a PBP in resistance to host AMPs.     

Molecular characterization of nontypeable group B streptococcus

Traditionally, the capsular polysaccharide (CPS) antigen has been used to distinguish between the nine known serotypes of group B streptococcus (GBS) by classical antibody-antigen reactions. In this study, we used PCR for all CPSs and selected protein antigens, multilocus sequencing typing (MLST), and pulsed-field gel electrophoresis (PFGE) to molecularly characterize 92 clinical isolates identified as nontypeable (NT) by CPS-specific antibody-antigen reactivity. The PCR and MLST were performed on blinded, randomly numbered isolates. All isolates contained the cfb gene coding for CAMP factor. While most (56.5%) contained a single CPS-specific gene, 40 isolates contained either two or three CPS-specific genes. Type V CPS-specific gene was present in 66% of the isolates, and all serotypes except types IV, VII, and VIII were represented. Most (44.5%) of the isolates contained a single protein antigen gene (bca, bac, rib, alp1, or alp3), and the remaining isolates had multiple protein antigen genes. Of the 61 isolates that had the V CPS-specific gene, 48 (78.6%) had the alp3 gene. PFGE analysis classified the isolates into 21 profile groups, while MLST analysis divided the isolates into 16 sequence types. Forty-two (69%) of 61 isolates with the V CPS-specific gene were in PFGE profile group 4; 41 of these 42 were sequence type 1 by MLST. These data shed new light on the antigenic complexity of NT GBS isolates, information that can be valuable in the formulation of an effective GBS vaccine.     

Pilot-scale production of group a and group C meningococcal polysaccharide immunogens

Methods have been developed for the pilot-scale production of group A and group C meningococcal polysaccharide immunogens based on the meningococcal strains, the medium, and the basic processing procedures used by Gotschlich et al. Physical and chemical assays on the final products obtained on a pilot-scale level indicate that these purified polysaccharides are entirely comparable to the Gotschlich preparations which proved to be immunogenic in man.     

Identification of a specific receptor for plasmin on a group A streptococcus

Certain group A streptococci demonstrate surface receptors that bind selectively to the key fibrinolytic enzyme, plasmin. These bacteria show no reactivity with the zymogen protein plasminogen or with other serine class proteases, such as trypsin or urokinase. Bacterium-bound plasmin retains its ability to cleave synthetic substrates and its ability to hydrolyze a fibrin clot. The bacterium-bound plasmin is not effectively regulated by its physiological regulator, alpha 2-plasmin inhibitor. This study is the first report of a bacterium-associated receptor for plasmin.     

Immunoglobulin M and G antibody responses and persistence of these antibodies in adults after vaccination with a combined meningococcal group A and group C polysaccharide vaccine.

Adult volunteers were injected with a combined meningococcal group A and group C polysaccharide vaccine. Immunoglobulin M (IgM) and IgG antibody levels against both polysaccharides were measured in serum samples taken 14 days as well as 3 years after vaccination. For both group A and group C polysaccharides, the IgM and IgG antibody levels at 14 days postvaccination were positively related. The IgM-to-IgG antibody ratio at 14 days postvaccination was an indicator for the persistence of both IgM and IgG antibodies during the next 3 years; a high ratio meant a short persistence, whereas a low ratio was associated with a long persistence.