Characterization of group B streptococcal invasion of human chorion and amnion epithelial cells In vitro

Spatial profiling of the placental chorioamniotic membranes reveals upregulation of immune checkpoint proteins during Group B Streptococcus infection in a nonhuman primate model

Background

Preterm birth is a leading cause of neonatal mortality, which is often complicated by intrauterine infection and inflammation. We have established a nonhuman primate model of Group B Streptococcus (GBS, Streptococcus agalactiae) infection-associated preterm birth. Immune checkpoints are modulators of the immune response by activating or suppressing leukocyte function and are understudied in preterm birth. The objective of this study was to spatially profile changes in immune protein expression at the maternal-fetal interface during a GBS infection with a focus on immune checkpoints.

Methods

Twelve nonhuman primates (pigtail macaques, Macaca nemestrina) received a choriodecidual inoculation of either: 1) 1-5 X 108 colony forming units (CFU) of hyperhemolytic/hypervirulent GBS (GBSΔcovR, N=4); 2) an isogenic/nonpigmented strain (GBS ΔcovRΔcylE, N=4); or, 3) saline (N=4). A Cesarean section was performed at preterm labor or 3 days after GBS infection or 7 days after saline inoculation. Nanostring GeoMx® Digital Spatial Profiling technology was used to segment protein expression within the amnion, chorion, and maternal decidua at the inoculation site using an immuno-oncology panel targeting 56 immunoproteins enriched in stimulatory and inhibitory immune checkpoint proteins or their protein ligands. Statistical analysis included R studio, Kruskal-Wallis, Pearson and Spearman tests.

Results

Both inhibitory and stimulatory immune checkpoint proteins were significantly upregulated within the chorioamniotic membranes and decidua (VISTA, LAG3, PD-1, CD40, GITR), as well as their ligands (PD-L1, PD-L2, CD40L; all p<0.05). Immunostaining for VISTA revealed positive (VISTA+) cells, predominantly in the chorion and decidua. There were strong correlations between VISTA and amniotic fluid concentrations of IL-1β, IL-6, IL-8, and TNF-α (all p<0.05), as well as maternal placental histopathology scores (p<0.05).

Conclusion

Differential regulation of multiple immune checkpoint proteins in the decidua at the site of a GBS infection indicates a major perturbation in immunologic homeostasis that could benefit the host by restricting immune-driven pathologies or the pathogen by limiting immune surveillance. Protein expression of VISTA, an inhibitory immune checkpoint, was upregulated in the chorion and decidua after GBS infection. Investigating the impact of innate immune cell expression of inhibitory immune checkpoints may reveal new insights into placental host-pathogen interactions at the maternal-fetal interface.

A group B Streptococcus indexed transposon mutant library to accelerate genetic research on an important perinatal pathogen

IMPORTANCE

Group B Streptococcus (GBS) is a significant global cause of serious infections, most of which affect pregnant women, newborns, and infants. Studying GBS genetic mutant strains is a valuable approach for learning more about how these infections are caused and is a key step toward developing more effective preventative and treatment strategies. In this resource report, we describe a newly created library of defined GBS genetic mutants, containing over 1,900 genetic variants, each with a unique disruption to its chromosome. An indexed library of this scale is unprecedented in the GBS field; it includes strains with mutations in hundreds of genes whose potential functions in human disease remain unknown. We have made this resource freely available to the broader research community through deposition in a publicly funded bacterial maintenance and distribution repository.

Group B Streptococcus and Pregnancy: Critical Concepts and Management Nuances

Importance

Group B Streptococcus (GBS) is a common pathogen with an effective treatment. However, it remains a significant cause of neonatal sepsis, morbidity, and mortality. The screening and management of this infection are some of the first concepts learned during medical training in obstetrics. However, effective screening and evidence-based management of GBS are nuanced with many critical caveats.

Objective

The objectives of this review are to discuss the essential aspects of GBS screening and management and to highlight recent changes to recommendations and guidelines.

Evidence Acquisition

Original research articles, review articles, and guidelines on GBS were reviewed.

Results

The following recommendations are based on review of the evidence and professional society guidelines. Screening for GBS should occur between 36 weeks and the end of the 37th week. The culture swab should go 2 cm into the vagina and 1 cm into the anus. Patients can perform their own swabs as well. Penicillin allergy testing has been shown to be safe in pregnancy. Patients with GBS in the urine should be treated at term with antibiotic prophylaxis, independent of the colony count of the culture. Patients who are GBS-positive with preterm and prelabor rupture of membranes after 34 weeks are not candidates for expectant management, as this population has higher rates of neonatal infectious complications. Patients with a history of GBS colonization in prior pregnancy who are GBS-unknown in this current pregnancy and present with labor should receive intrapartum prophylaxis. Work on the GBS vaccine continues.

Conclusions

Although all of the efforts and focus on neonatal early-onset GBS infection have led to lower rates of disease, GBS still remains a major cause of neonatal morbidity and mortality requiring continued vigilance from obstetric providers.

A group B Streptococcus alpha-like protein subunit vaccine induces functionally active antibodies in humans targeting homotypic and heterotypic strains

Maternal vaccination is a promising strategy for preventing neonatal disease caused by group B Streptococcus. The safety and immunogenicity of the prototype vaccine GBS-NN, a fusion protein consisting of the N-terminal domains of the alpha-like proteins (Alp) αC and Rib, were recently evaluated favorably in healthy adult women in a phase 1 trial. Here we demonstrate robust immunoglobulin G (IgG) and immunoglobulin A (IgA) responses against αC and Rib, as well as against the heterotypic Alp family members Alp1–Alp3. IgA and heterotypic IgG responses are more variable between subjects and correlate with pre-existing immunity. Vaccine-induced IgG mediates opsonophagocytic killing and prevents bacterial invasion of epithelial cells. Like the vaccine-induced response, naturally acquired IgG against the vaccine domains is dominated by IgG1. Consistent with the high IgG1 cross-placental transfer rate, naturally acquired IgG against both domains reaches higher concentrations in neonatal than maternal blood, as assessed in a separate group of non-vaccinated pregnant women and their babies.

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GBS-NN subunit vaccine broadly elicits IgG1 to homotypic αC and Rib N-terminal domains

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IgA and heterotypic IgG responses occur in vaccinees with pre-existing immunity

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Abs mediate opsonophagocytic killing and prevent bacterial epithelial cell invasion

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IgG against αC-N and Rib-N is transferred efficiently across the placenta

IgGFc-binding protein in pregnancies complicated by spontaneous preterm delivery: a retrospective cohort study

To determine the IgGFc-binding protein (FcgammaBP) concentration in amniotic and cervical fluids in preterm prelabor rupture of membranes (PPROM) and preterm labor with intact membranes (PTL) and to assess the diagnostic indices of FcgammaBP to predict intra-amniotic infection (the presence of both microbial invasion of the amniotic cavity and intra-amniotic inflammation). In this study, we included 170 and 79 women with PPROM and PTL, respectively. Paired cervical and amniotic fluid samples were obtained using a Dacron polyester swab and transabdominal amniocentesis, respectively. The FcgammaBP concentrations in the samples were assessed using an enzyme-linked immunosorbent assay. The presence of intra-amniotic infection was associated with elevated FcgammaBP concentrations in pregnancies with PPROM and PTL [PPROM—presence: 86 ng/mL vs. absence: 13 ng/mL, p < 0.0001, area under receiver operating characteristic curve (AUC) = 0.94; PTL—presence: 140 ng/mL vs. absence: 22 ng/mL, p < 0.0001, AUC = 0.86]. In cervical fluid, the concentrations of FcgammaBP were elevated in the presence of intra-amniotic infection in pregnancies with PPROM only (presence: 345 ng/mL vs. absence: 60 ng/mL, p < 0.0001, AUC = 0.93). FcgammaBP in amniotic fluid might be a marker of intra-amniotic infection in women with both PPROM and PTL However, in cervical fluid, it is only observed in women with PPROM.

Protein kinase D mediates inflammatory responses of human placental macrophages to Group B Streptococcus

PROBLEM

During pregnancy, Group B Streptococcus (GBS) can infect fetal membranes to cause chorioamnionitis, resulting in adverse pregnancy outcomes. Macrophages are the primary resident phagocyte in extraplacental membranes. Protein kinase D (PKD) was recently implicated in mediating pro-inflammatory macrophage responses to GBS outside of the reproductive system. This work aimed to characterize the human placental macrophage inflammatory response to GBS and address the extent to which PKD mediates such effects.

METHOD

Primary human placental macrophages were infected with GBS in the presence or absence of a specific, small molecule PKD inhibitor, CRT 0066101. Macrophage phenotypes were characterized by evaluating gene expression, cytokine release, assembly of the NLRP3 inflammasome, and NFκB activation.

RESULTS

GBS evoked a strong inflammatory phenotype characterized by the release of inflammatory cytokines (TNFα, IL-1β, IL-6 (P ≤ 0.05), NLRP3 inflammasome assembly (P ≤ 0.0005), and NFκB activation (P ≤ 0.05). Pharmacological inhibition of PKD suppressed these responses, newly implicating a role for PKD in mediating immune responses of primary human placental macrophages to GBS.

CONCLUSION

PKD plays a critical role in mediating placental macrophage inflammatory activation in response to GBS infection.

Causal role of group B Streptococcus-induced acute chorioamnionitis in intrauterine growth retardation and cerebral palsy-like impairments

Chorioamnionitis and intrauterine growth retardation (IUGR) are risk factors for cerebral palsy (CP). Common bacteria isolated in chorioamnionitis include group B Streptococcus (GBS) serotypes Ia and III. Little is known about the impact of placental inflammation induced by different bacteria, including different GBS strains. We aimed to test the impact of chorioamnionitis induced by two common GBS serotypes (GBSIa and GBSIII) on growth and neuromotor outcomes in the progeny. Dams were exposed at the end of gestation to either saline, inactivated GBSIa or GBSIII. Inactivated GBS bacteria invaded placentas and triggered a chorioamnionitis featured by massive polymorphonuclear cell infiltrations. Offspring exposed to GBSIII - but not to GBSIa - developed IUGR, persisting beyond adolescent age. Male rats in utero exposed to GBSIII traveled a lower distance in the Open Field test, which was correlating with their level of IUGR. GBSIII-exposed rats presented decreased startle responses to acoustic stimuli beyond adolescent age. GBS-exposed rats displayed a dysmyelinated white matter in the corpus callosum adjacent to thinner primary motor cortices. A decreased density of microglial cells was detected in the mature corpus callosum of GBSIII-exposed males - but not females - which was correlating positively with the primary motor cortex thickness. Altogether, our results demonstrate a causal link between pathogen-induced acute chorioamnionitis and (1) IUGR, (2) serotype- and sex-specific neuromotor impairments and (3) abnormal development of primary motor cortices, dysmyelinated white matter and decreased density of microglial cells.

Sex-Dependent Influence of Developmental Toxicant Exposure on Group B Streptococcus-Mediated Preterm Birth in a Murine Model

Infectious agents are a significant risk factor for preterm birth (PTB); however, the simple presence of bacteria is not sufficient to induce PTB in most women. Human and animal data suggest that environmental toxicant exposures may act in concert with other risk factors to promote PTB. Supporting this "second hit" hypothesis, we previously demonstrated exposure of fetal mice (F1 animals) to the environmental endocrine disruptor 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) leads to an increased risk of spontaneous and infection-mediated PTB in adult animals. Surprisingly, adult F1_males also confer an enhanced risk of PTB to their control partners. Herein, we used a recently established model of ascending group B Streptococcus (GBS) infection to explore the impact of a maternal versus paternal developmental TCDD exposure on infection-mediated PTB in adulthood. Group B Streptococcus is an important contributor to PTB in women and can have serious adverse effects on their infants. Our studies revealed that although gestation length was reduced in control mating pairs exposed to low-dose GBS, dams were able to clear the infection and bacterial transmission to pups was minimal. In contrast, exposure of pregnant F1_females to the same GBS inoculum resulted in 100% maternal and fetal mortality. Maternal health and gestation length were not impacted in control females mated to F1_males and exposed to GBS; however, neonatal survival was reduced compared to controls. Our data revealed a sex-dependent impact of parental TCDD exposure on placental expression of Toll-like receptor 2 and glycogen production, which may be responsible for the differential impact on fetal and maternal outcomes in response to GBS infection.

Perinatal Group B Streptococcal Infections: Virulence Factors, Immunity, and Prevention Strategies

Group B streptococcus (GBS) or Streptococcus agalactiae is a β-hemolytic, Gram-positive bacterium that is a leading cause of neonatal infections. GBS commonly colonizes the lower gastrointestinal and genital tracts and, during pregnancy, neonates are at risk of infection. Although intrapartum antibiotic prophylaxis during labor and delivery has decreased the incidence of early-onset neonatal infection, these measures do not prevent ascending infection that can occur earlier in pregnancy leading to preterm births, stillbirths, or late-onset neonatal infections. Prevention of GBS infection in pregnancy is complex and is likely influenced by multiple factors, including pathogenicity, host factors, vaginal microbiome, false-negative screening, and/or changes in antibiotic resistance. A deeper understanding of the mechanisms of GBS infections during pregnancy will facilitate the development of novel therapeutics and vaccines. Here, we summarize and discuss important advancements in our understanding of GBS vaginal colonization, ascending infection, and preterm birth.

Group B Streptococcus and perinatal mortality

The World Health Organization estimates that every year, one million neonatal deaths occur because of neonatal infection. Furthermore, an equal number of stillbirths are thought to be caused by infections. Here we discuss the role of Streptococcus agalactiae (group B Streptococcus, GBS) in neonatal disease and stillbirth.

Differential Secretion of Matrix Metalloproteinase-2 and -9 After Selective Infection With Group B Streptococci in Human Fetal Membranes

OBJECTIVE

This study evaluated the secretions of zymogen and active forms of matrix metalloproteinase (MMP)-9 and MMP-2 and their specific inhibitors, TIMP-1 and TIMP-2 by fetal membranes stimulated with group B Streptoccocci (GBS).

METHODS

We used an in vitro experimental model that allowed us to estimate the individual contribution of the amnion (AM) and the choriodecidua (CHD) to the microbial insult. Membranes were obtained after delivery by elective cesarean delivery from women at 37 to 40 weeks of gestation without evidence of either active labor or intrauterine infection. Membranes were mounted in Transwell devices (Costar, New York, NY), physically separating the upper and lower chambers; 1 x 10(6) CFU of GBS was added to either AM or CHD and the secretions and gelatinolytic activity of MMP-2 and MMP-9 were measured in both compartments by enzyme-linked immunosorbent assay (ELISA) and zymography. TIMPs secretion was measured by ELISA. Both MMPs were immunolocalized in tissue sections.

RESULTS

The simultaneous stimulation at both sides was followed by increases of proMMP-9 (85.0 +/- 18.63 pg/mL) and proMMP-2 (4.10 +/- 1.90 ng/mL) in the CHD (P <.05). When only one side of the membrane was stimulated, the secretion level of proMMP-2 increased 2.3-fold and that of proMMP-9 2.5-fold in the CHD. The active forms of both enzymes did not change with any modality of stimulation. The secretion level of both TIMPs remained without significant changes. CHD and AM were positive for immunoreactive MMP-2 and MMP-9.

CONCLUSION

We propose that infection of fetal membranes with GBS is followed by active secretion of MMP and the CHD is the principal source of these mediators of extracellular matrix degradation.

The bacterial etiology of preterm birth

Preterm birth is the leading cause of infant morbidity and mortality. Very preterm births, those occurring before 32 completed weeks of gestation, are associated with the greatest risks. The leading cause of very preterm birth is intrauterine infection, which can lead to an inflammatory response that triggers labor or preterm premature rupture of membranes. How bacteria invade the uterine cavity, which is normally a sterile environment, and the reasons why different species vary in their capacity to induce inflammation and preterm birth are still incompletely understood. However, advanced techniques that circumvent the need for cultivating bacteria, deep sequence analysis that allows for the comprehensive characterization of the microbiome of a given body site and detection of low-prevalence species, and transcriptomics and metabolomics approaches that shed light on the host response to bacterial invasion are all providing a more complete picture of the progression from vaginal colonization to uterine invasion to preterm labor and preterm birth.

Group B streptococcus alters properties of vaginal epithelial cells in pregnant women

BACKGROUND

Group B streptococcus (GBS) infection in pregnancy is a major cause of maternal and neonatal morbidity. An understanding of the mechanisms responsible for GBS persistence in the genital tract, as well as recognition of host defenses employed to combat its presence, are crucial to our efforts to reduce maternal GBS colonization and prevent the acquisition of neonatal infections. However, alterations in vaginal immunity in response to GBS colonization in pregnant women remain incompletely defined. Whether GBS modulates autophagy, a major host defense mechanism and contributor to the control of intracellular microbial infections, also remains unclear.

OBJECTIVE

We sought to identify differences in the extent of autophagy as well as in the concentration of biomarkers previously shown to be involved in vaginal innate immunity between GBS-positive and GBS-negative pregnant women.

STUDY DESIGN

We performed a prospective cohort study of healthy pregnant women, who had vaginal secretions obtained at 35-37 weeks of gestation, just prior to the standard GBS rectovaginal sample collection. The contents of the swabs were released into tubes containing 1 mL of sterile phosphate-buffered saline. Samples were centrifuged, and supernatant and cell pellet fractions were collected and stored separately at -80°C until used for analysis. Epithelial cells were then lysed, and the extent of autophagy was determined by measuring the residual level of p62 remaining in the cytoplasm. p62 is a protein that is consumed during autophagy, and so its concentration detectable in the cytoplasm is inversely related to the extent of autophagy induction. The intracellular level of the inducible 70-kDa heat shock protein (hsp70), an inhibitor of autophagy, was also measured. The cell-free fraction was assayed for D- and L-lactic acid, neutrophil gelatinase-associated lipocalin, extracellular matrix metalloproteinase inducer (EMMPRIN), matrix metalloproteinase (MMP)-8, alpha amylase, hyaluronan, and total protein. Laboratory personnel were blinded to all clinical data.

RESULTS

There were 145 women included in the study, of which 45 (31%) were culture-positive for GBS. Vaginal cells from GBS-positive women had elevated intracellular levels of p62 (2.1 vs 0.7 pg/mL, P < .01) and hsp70 (16.9 vs 9.6 ng/mL, P = .03) as compared to GBS-negative women. The p62 and hsp70 levels were highly correlated in both groups of subjects (P < .01). In vaginal fluid, concentrations of neutrophil gelatinase-associated lipocalin (1.1 vs 0.7 ng/μg total protein, P = .01), MMP-8 (21.9 vs 11.1 pg/μg total protein, P = .01), and extracellular MMP inducer (8.8 vs 7.2 pg/μg total protein, P = .03) were highest in GBS-positive women. There were no differences in the concentrations of D- and L-lactic acid, alpha amylase, or hyaluronan between the 2 groups of women.

CONCLUSION

The inhibition of autophagy in vaginal epithelial cells by GBS-induced hsp70 production is associated with its persistence. Concurrently, alterations in components known to influence vaginal bacterial colonization or facilitate microbial passage to the upper genital tract also occur in relation to GBS carriage.

Group B streptococcal infection and activation of human astrocytes

Background

Streptococcus agalactiae (Group B Streptococcus, GBS) is the leading cause of life-threatening meningitis in human newborns in industrialized countries. Meningitis results from neonatal infection that occurs when GBS leaves the bloodstream (bacteremia), crosses the blood-brain barrier (BBB), and enters the central nervous system (CNS), where the bacteria contact the meninges. Although GBS is known to invade the BBB, subsequent interaction with astrocytes that physically associate with brain endothelium has not been well studied.

Methodology/Principal Findings

We hypothesize that human astrocytes play a unique role in GBS infection and contribute to the development of meningitis. To address this, we used a well- characterized human fetal astrocyte cell line, SVG-A, and examined GBS infection in vitro. We observed that all GBS strains of representative clinically dominant serotypes (Ia, Ib, III, and V) were able to adhere to and invade astrocytes. Cellular invasion was dependent on host actin cytoskeleton rearrangements, and was specific to GBS as Streptococcus gordonii failed to enter astrocytes. Analysis of isogenic mutant GBS strains deficient in various cell surface organelles showed that anchored LTA, serine-rich repeat protein (Srr1) and fibronectin binding (SfbA) proteins all contribute to host cell internalization. Wild-type GBS also displayed an ability to persist and survive within an intracellular compartment for at least 12 h following invasion. Moreover, GBS infection resulted in increased astrocyte transcription of interleukin (IL)-1β, IL-6 and VEGF.

Conclusions/Significance

This study has further characterized the interaction of GBS with human astrocytes, and has identified the importance of specific virulence factors in these interactions. Understanding the role of astrocytes during GBS infection will provide important information regarding BBB disruption and the development of neonatal meningitis.

False vs True rupture of membranes

New medical nomenclature: False rupture of membranes or False ROM and Double rupture of membranes or Double ROM are being introduced into the English language. A single caregiver found about 1% of term births and 10% of term PROM involved False ROM, in which the chorion breaks while the amnion remains intact. Diagnostically, if meconium or vernix is observed, then both the chorionic and amniotic sacs have broken. In the absence of detection of vernix or meconium, an immediate accurate diagnostic test for False ROM is lacking and differentiating between True ROM from False ROM is possible only after leaking stops, which takes hours to days. The obvious benefit of differentiating between 'True' and 'False' ROM, is that in the case of False ROM, the amnion is intact and ascending infections are likely not at increased risk, although research is lacking as to whether False ROM is associated with an increased rate of ascending infection. Three cases of False ROM are presented and avenues for future research are enumerated.

Association and virulence gene expression vary among serotype III group B streptococcus isolates following exposure to decidual and lung epithelial cells

Group B Streptococcus (GBS) causes severe disease in neonates, the elderly, and immunocompromised individuals. GBS species are highly diverse and can be classified by serotype and multilocus sequence typing. Sequence type 17 (ST-17) strains cause invasive neonatal disease more frequently than strains of other STs. Attachment and invasion of host cells are key steps in GBS pathogenesis. We investigated whether four serotype III strains representing ST-17 (two strains), ST-19, and ST-23 differ in their abilities to attach to and invade both decidual cells and lung epithelial cells. Virulence gene expression following host cell association and exposure to amnion cells was also tested. The ST-17 strains differed in their abilities to attach to and invade decidual cells, whereas there were no differences with lung epithelial cells. The ST-19 and ST-23 strains, however, attached to and invaded decidual cells less than both ST-17 strains. Although the ST-23 strain attached to lung epithelial cells better than ST-17 and -19 strains, none of the strains effectively invaded the lung epithelial cells. Notably, the association with host cells resulted in the differential expression of several virulence genes relative to basal expression levels. Similar expression patterns of some genes were observed regardless of cell type used. Collectively, these results show that GBS strains differ in their abilities to attach to distinct host cell types and express key virulence genes that are relevant to the disease process. Enhancing our understanding of pathogenic mechanisms could aid in the identification of novel therapeutic targets or vaccine candidates that could potentially decrease morbidity and mortality associated with neonatal infections.

[Maternal and perinatal infections to Streptococcus agalactiae]

Streptococcus agalactiae (Group B Streptococcus, GBS) is a Gram-positive encapsulated bacterium, found in the digestive and vaginal tracts of 20-30% healthy individuals. It is the leading cause of neonatal invasive infections (septicaemia and meningitis). Two GBS-associated syndromes have been recognized in neonates, the early-onset disease (EOD) and the late-onset disease (LOD), which occur in the first week of life (age 0-6 days) and after (age 7 days-3 months), respectively. Since the establishment of early antibiotic prophylaxis there has been a decrease in the incidence of EOD. However, LOD incidence remains stable. Epidemiological studies revealed a strong association between LOD and a single capsular serotype III ST-17 clone. This ST-17 clone, referred to as the "hypervirulent" clone, possesses specific virulence factors that could account for its increased virulence and neonatal tropism. Conjugate vaccines directed against several capsular serotypes are being developed to prevent invasive disease. However, hypervirulent strains having made a switch to a capsular serotype not covered by such vaccines are emerging, reinforcing the need to identify new candidate vaccines.

A hemolytic pigment of Group B Streptococcus allows bacterial penetration of human placenta

Microbial infection of the amniotic fluid is a significant cause of fetal injury, preterm birth, and newborn infections. Group B Streptococcus (GBS) is an important human bacterial pathogen associated with preterm birth, fetal injury, and neonatal mortality. Although GBS has been isolated from amniotic fluid of women in preterm labor, mechanisms of in utero infection remain unknown. Previous studies indicated that GBS are unable to invade human amniotic epithelial cells (hAECs), which represent the last barrier to the amniotic cavity and fetus. We show that GBS invades hAECs and strains lacking the hemolysin repressor CovR/S accelerate amniotic barrier failure and penetrate chorioamniotic membranes in a hemolysin-dependent manner. Clinical GBS isolates obtained from women in preterm labor are hyperhemolytic and some are associated with covR/S mutations. We demonstrate for the first time that hemolytic and cytolytic activity of GBS is due to the ornithine rhamnolipid pigment and not due to a pore-forming protein toxin. Our studies emphasize the importance of the hemolytic GBS pigment in ascending infection and fetal injury.

Antimicrobial peptide response to group B Streptococcus in human extraplacental membranes in culture

OBJECTIVE

Streptococcus agalactiae (GBS) is an important cause of chorioamnionitis. This study characterizes GBS colonization and stimulation of antimicrobial responses in human extraplacental membranes using an ex vivo transwell two-compartment system of full-thickness membranes and live GBS.

STUDY DESIGN

Human extraplacental membranes were affixed to transwell frames (without synthetic membranes). Live GBS was added to the decidual side of membranes in transwell cultures, and cocultures were incubated for 4, 8 and 24 h. GBS recovery from homogenized membranes and culture medium was determined by enumerating colony forming units (CFU) on blood agar. Antimicrobial peptide expression was identified using immunohistochemistry and ELISA. GBS killing by HBDs was assessed in vitro by incubating GBS with different human beta defensins (HBDs) for 3 h, then enumerating CFU.

RESULTS

GBS recovery from membranes markedly decreased over time (P < 0.05). The antimicrobial peptides HBD-1, HBD-2, HBD-3, and lactoferrin were expressed in both GBS-exposed and non-exposed tissues. Notably, a pattern of localized increased HBD-2 in the amnion of GBS-infected tissue was observed. Moreover, GBS-treated membranes released increased amounts of HBD-2 into the amniotic and decidual compartments of the transwell cultures after 24 h (P < 0.05). In bacterial cultures, HBD-2 decreased GBS viability in a concentration-dependent manner (P < 0.05).

CONCLUSION

Innate immune responses in ex vivo human extraplacental membranes suppress GBS growth. HBD-2 was implicated in this GBS suppression with evidence of signal transduction across the tissue. Antimicrobial peptides may be important for innate immune defense against intrauterine GBS infections during pregnancy.

Advances in medical diagnosis of intra-amniotic infection

INTRODUCTION

Intrauterine infection is a global problem and a significant contributor to morbidity and perinatal death. The host response to infection causes an inflammatory state that acts synergistically with microbial insult to induce preterm birth and fetal damage. Prompt and accurate diagnosis of intra-amniotic infection in the asymptomatic stage of the disease is critical for improved maternal and neonatal outcomes.

AREAS COVERED

This article provides an overview of the most recent progress, challenges, and opportunities for discovery and clinical implementation of various maternal serum, cervicovaginal, and amniotic fluid biomarkers in pregnancies complicated by intra-amniotic infection.

EXPERT OPINION

Clinically relevant biomarkers are critical to the accurate diagnostic of intrauterine infection. Front-end implementation of such biomarkers will also translate in lower incidence of early-onset neonatal sepsis (EONS) which is an important determinant of neonatal morbidity and mortality associated with prematurity. However, of the hundreds of differentially expressed proteins, only few may have clinical utility and thus function as biomarkers. The small number of validation studies along with barriers to implementation of technological innovations in the clinical setting are current limitations.

Group B Streptococcus interactions with human meningeal cells and astrocytes in vitro

BACKGROUND

Streptococcus agalactiae (Group B Streptococcus, GBS) is a leading cause of life-threatening neonatal meningitis and survivors often suffer permanent neurological damage. How this organism interacts with the meninges and subsequently with astrocytes that constitute the underlying cortical glia limitans superficialis is not known.

METHODOLOGY/PRINCIPAL FINDINGS

In this paper, we demonstrate dose-dependent adherence of GBS over time to human meningioma cells and fetal astrocytes in vitro, which was not influenced by expression of either β-haemolysin/cytolysin (β-h/c) toxin, different capsule serotypes or by absence of capsule (p>0.05). Internalization of GBS by both cell types was, however, a slow and an infrequent event (only 0.02-0.4% of associated bacteria were internalised by 9 h). Expression of β-h/c toxin did not play a role in invasion (p>0.05), whereas capsule expression lead to a reduction (p<0.05) in the numbers of intracellular bacteria recovered. GBS strains induced cytotoxicity as demonstrated by the measurement of lactate dehydrogenase (LDH) enzyme release by 9 h and by viable staining. Increasing levels of meningioma cell death correlated with bacterial growth and the phenotype of β-h/c toxin production, i.e. from weakly, to normo- to hyper-haemolytic. However, cytotoxicity was significantly greater (p<0.05) towards astrocytes, and infection with initial MOI≥0.003 induced 70-100% LDH release. By comparing wild-type (β-h/c(+)) and mutant (ΔcylE β-h/c(-)) strains and β-h/c toxin extracts and by using the surfactant dipalmitoylphosphatidylcholine in cytotoxicity inhibition experiments, β-h/c toxin was demonstrated as principally responsible for cell death.

CONCLUSIONS/SIGNIFICANCE

This study has described key events in the interactions of GBS with meningeal cells and astrocytes in vitro and a major virulence role for β-h/c toxin. Understanding the mechanisms involved will help to identify potential therapies for improving patient survival and for reducing the incidence and severity of neurological sequelae.

An experimental mixed bacterial infection induced differential secretion of proinflammatory cytokines (IL-1β, TNFα) and proMMP-9 in human fetal membranes

Overall, 1-4% of all births in the US are complicated by choriamnionitis. Choriamnionitis is a polymicrobial infection most often due to ascending genital microbes which, in over 65% of positive amniotic fluid cultures, involves two or more organisms. In this study, we determine the cytokines expression (IL-1β, TNFα) and prometalloproteinase activation (proMMP-2 and proMMP-9) after double o single infection an in vitro model of human fetal membranes. Fetal membranes at term were mounted in the Transwell culture system and after 24 h of infection, choriodecidual, and amnion media was collected. IL-1β and TNFα were evaluated by ELISA, whereas proMMP-9 and proMMP-2 were determined by substrate gel zymography. The choriodecidual and amnion compartments actively respond to the infectious process, which induced the secretion of IL-1β, TNFα, and proMMP-9 after either mixed or single infection. The proMMP-2 secretion profile was the same after all experimental conditions. There was no synergy between Streptococcus agalactiae and Escherichia coli for inducing the secretion of inflammatory factors or degradative metalloproteinase. In conclusion, these two bacteria could initiate different pathways to induce chorioamnioitis.

Binding of group B streptococcal phosphoglycerate kinase to plasminogen and actin

The glycolytic enzyme, phosphoglycerate kinase (PGK) of group B streptococci (GBS), has previously been identified as expressed on the GBS cell surface. The data presented describes the ability of group B streptococcal phosphoglycerate kinase (GBS-PGK) to bind to plasminogen and to bind actin. GBS-PGK binding to plasminogen was inhibited by the lysine analogue, 6-aminocaproic acid, suggesting plasminogen binding is achieved through GBS-PGK lysine residues. In addition to GBS-PGK surface expression, GBS-PGK was also found to be released from the bacterial cell suggesting GBS-PGK may affect its environment independent of GBS. To determine the effect of GBS-PGK on the actin cytoskeleton within a host cell, GBS-PGK attached to green fluorescent protein was transfected into and expressed in HeLa cells. Transfected GBS-PGK disrupted the actin cytoskeleton resulting in a compact or ovoid shaped HeLa cell rather than a typical epithelioid appearance. In conclusion, we have shown GBS-PGK binds to plasminogen and actin. We have also shown that GBS-PGK can be released from the bacterial cell and that transfected GBS-PGK can alter the epithelial cell cytoskeleton.

Evidence of in vitro differential secretion of human beta-defensins-1, -2, and -3 after selective exposure to Streptococcus agalactiae in human fetal membranes

OBJECTIVE

The aim of this work was to characterize the individual contribution of the amnion (AMN) and choriodecidua (CHD) regions to the secretion of human beta defensins (HBD)-1, -2, and -3, after stimulation with Streptococcus agalactiae.

METHODS

Full-thickness membranes were mounted on a Transwell device, constituted by two independent chambers; 1 × 10(6) CFU/ml of S. agalactiae were added to either the AMN or CHD face or to both. Secretion profiles of HBD-1, HBD-2, and HBD-3 to the culture medium were quantified by enzyme-linked immunosorbent sandwich assay (ELISA).

RESULTS

Secretion profile of HBD-1 remained without significant changes; HBD-2 secretion level by the CHD increased 2.0 (2.73 ± 0.19 pg/μg) and 2.6 (3.62 ± 0.60 pg/μg) times when the stimulus was applied only to the CHD region and simultaneously to both compartments, respectively. The bacterial stimulation in the AMN induced a 2.0 times (2.06 ± 0.29 pg/μg) increase in this region. HBD-3 secretion level increased significantly in the CHD (15.65 ± 2.68 pg/μg) and the AMN (14.94 ± 1.85 pg/μg) only when both regions were stimulated simultaneously.

CONCLUSION

The stimulation of human fetal membranes with S. agalactiae induced a differential and tissue-specific profile of HBD-1, HBD-2, and HBD-3 secretion.

Choriodecidual inflammation: a harbinger of the preterm labor syndrome

Causal, cellular, and inflammatory links between choriodecidual infection with group B streptococcus (GBS) and preterm labor were assessed in a nonhuman primate model. Rhesus monkeys received varying doses of a clinical isolate of GBS, type III or saline, via an indwelling catheter placed between the chorion/decidua and myometrium in the lower pole of the uterus. Choriodecidual inoculation of GBS was followed by a graded response in amniotic fluid (AF) leukocytes, proinflammatory cytokines, prostaglandin E(2) and F(2alpha), and uterine activity (P < .05). The magnitude of the inflammatory response in AF was related, in part, to the initial inoculum size and whether AF cultures remained negative or became positive for GBS. Microbial invasion of AF was associated with advanced inflammation and preterm labor. We provide experimental evidence that choriodeciduitis is a transitional stage of intrauterine infection, which may be self-limited, remain dormant, or progress to intraamniotic infection. These data, coupled with clinical observations, suggest that choriodecidual inflammation is an antecedent event in the pathogenesis of premature cervical ripening (functional cervical insufficiency), premature rupture of the fetal membranes, or preterm labor.

The group B streptococcal serine-rich repeat 1 glycoprotein mediates penetration of the blood-brain barrier

BACKGROUND

Group B Streptococcus (GBS) is the leading cause of bacterial meningitis in newborn infants. Because GBS is able to invade, survive, and cross the blood-brain barrier, we sought to identify surface-expressed virulence factors that contribute to blood-brain barrier penetration and the pathogenesis of meningitis.

METHODS

Targeted deletion and insertional mutants were generated in different GBS clinical isolates. Wild-type and mutant bacteria were analyzed for their capacity to adhere to and invade human brain microvascular endothelial cells (hBMECs) and to penetrate the blood-brain barrier using our model of hematogenous meningitis.

RESULTS

Analysis of a GBS (serotype V) clinical isolate revealed the presence of a surface-anchored serine-rich protein, previously designated serine-rich repeat 1 (Srr-1). GBS Srr-1 is a glycosylated protein with high molecular weight. Deletion of srr1 in NCTC 10/84 resulted in a significant decrease in adherence to and invasion of hBMECs. Additional mutants in other GBS serotypes commonly associated with meningitis showed a similar decrease in hBMEC invasion, compared with parental strains. Finally, in mice, wild-type GBS penetrated the blood-brain barrier and established meningitis more frequently than did the Deltasrr1 mutant strain.

CONCLUSIONS

Our data suggest that GBS Srr glycoproteins play an important role in crossing the blood-brain barrier and in the development of streptococcal meningitis.

Recent advances in understanding the molecular basis of group B Streptococcus virulence

Group B Streptococcus commonly colonises healthy adults without symptoms, yet under certain circumstances displays the ability to invade host tissues, evade immune detection and cause serious invasive disease. Consequently, Group B Streptococcus remains a leading cause of neonatal pneumonia, sepsis and meningitis. Here we review recent information on the bacterial factors and mechanisms that direct host-pathogen interactions involved in the pathogenesis of Group B Streptococcus infection. New research on host signalling and inflammatory responses to Group B Streptococcus infection is summarised. An understanding of the complex interplay between Group B Streptococcus and host provides valuable insight into pathogen evolution and highlights molecular targets for therapeutic intervention.

Group B streptococcus induces trophoblast death

Group B streptococcus (GBS) is one of the leading causes of neonatal infection; however the molecular mechanisms involved are not clearly known. Here we used high and low hemolytic GBS isolates and mutant GBS that lacks beta-hemolysin expression and showed that GBS infection or exposure to GBS hemolysin extract induces primary human trophoblast, placental fibroblast and JEG3 trophoblast cell line death, and that GBS-induced trophoblast death was beta-hemolysin dependent. The fibroblasts and trophoblasts provide an innate immune barrier between fetal and maternal circulation in the placenta. These data suggest that GBS may disrupt this barrier to invade fetal circulation.

Group B Streptococcus: global incidence and vaccine development

An ongoing public health challenge is to develop vaccines that are effective against infectious diseases that have global relevance. Vaccines against serotypes of group B Streptococcus (GBS) that are prevalent in the United States and Europe are not optimally efficacious against serotypes common to other parts of the world. New technologies and innovative approaches are being used to identify GBS antigens that overcome serotype-specificity and that could form the basis of a globally effective vaccine against this opportunistic pathogen. This Review highlights efforts towards this goal and describes a template that can be followed to develop vaccines against other bacterial pathogens.

Outcomes in Gestations Between 20 and 25 Weeks with Preterm Premature Rupture of Membranes

BACKGROUND

Preterm deliveries complicate 11% of all births within the United States. In the urban inner city population, this figure approaches approximately 18%. In one quarter to one third of these deliveries, preterm premature rupture of the membranes (PPROM) has been a causative factor.

OBJECTIVE

The purpose of this study was to evaluate outcomes of pregnancies complicated by preterm premature rupture of membranes at less than or equal to 24 weeks gestation at our institution.

METHODS

A retrospective review of 300 charts was performed on patients delivered at our institution from December 2003 to December 2004. Patients with gestational ages between 20 and 24 weeks with ruptured membranes were included in the study. Maternal, fetal, placental, and neonatal characteristics were reviewed.

RESULTS

A total of 16 infants were delivered. Seven infants were live born. The latency period was 4 days. The mean gestational age was 22 1/7 weeks. The average life span of the live born infants was noted to be 20 days. Chorioamnionitis was demonstrated in 85% of the placental specimens; in 57% of these specimens, group B streptococcus was noted to be the etiologic agent. Of the 16 infants delivered, only one infant is still alive and neurologically intact.

CONCLUSION

Various pathogens have been associated with PPROM and subsequent preterm delivery. The findings of this study suggest that within our population, group B streptococcus appears to be the primary causal agent associated with PPROM. Prevention of infection by early surveillance and patient education may help to decrease the incidence, but further investigation is warranted.

Blood-brain barrier invasion by group B Streptococcus depends upon proper cell-surface anchoring of lipoteichoic acid

Group B streptococci (GBSs) are the leading cause of neonatal meningitis. GBSs enter the CNS by penetrating the blood-brain barrier (BBB), which consists of specialized human brain microvascular endothelial cells (hBMECs). To identify GBS factors required for BBB penetration, we generated random mutant libraries of a virulent strain and screened for loss of hBMEC invasion in vitro. Two independent hypo-invasive mutants possessed disruptions in the same gene, invasion associated gene (iagA), which encodes a glycosyltransferase homolog. Allelic replacement of iagA in the GBS chromosome produced a 4-fold decrease in hBMEC invasiveness. Mice challenged with the GBS DeltaiagA mutant developed bacteremia comparably to WT mice, yet mortality was significantly lower (20% vs. 90%), as was the incidence of meningitis. The glycolipid diglucosyldiacylglycerol, a cell membrane anchor for lipoteichoic acid (LTA) and predicted product of the IagA glycosyltransferase, was absent in the DeltaiagA mutant, which consequently shed LTA into the media. Attenuation of virulence of the DeltaiagA mutant was found to be independent of TLR2-mediated signaling, but bacterial supernatants from the DeltaiagA mutant containing released LTA inhibited hBMEC invasion by WT GBS. Our data suggest that LTA expression on the GBS surface plays a role in bacterial interaction with BBB endothelium and the pathogenesis of neonatal meningitis.

Growth rate and oxygen regulate the interactions of group B Streptococcus with polarized respiratory epithelial cells

We investigated growth conditions that regulate the ability of group B Streptococcus (GBS) to attach to, invade, and translocate through polarized human respiratory epithelial cells (RECs). GBS grown in a chemostat at a fast cell mass doubling time (t(d) = 1.8 h), invaded RECs from both the apical and basolateral surfaces in higher numbers compared with those held at a t(d) = 11 h. With the exception of adherence from the basolateral surface, GBS reached peak adherence to, invasion of, and translocation through RECs when held at the fast t(d) with 15% dissolved oxygen compared with 0% dissolved oxygen. Growth rate and oxygen level strongly influence the interaction of GBS with polarized RECs and likely GBS pathogenicity.

Surface proteins of Streptococcus agalactiae and related proteins in other bacterial pathogens

Streptococcus agalactiae (group B Streptococcus) is the major cause of invasive bacterial disease, including meningitis, in the neonatal period. Although prophylactic measures have contributed to a substantial reduction in the number of infections, development of a vaccine remains an important goal. While much work in this field has focused on the S. agalactiae polysaccharide capsule, which is an important virulence factor that elicits protective immunity, surface proteins have received increasing attention as potential virulence factors and vaccine components. Here, we summarize current knowledge about S. agalactiae surface proteins, with emphasis on proteins that have been characterized immunochemically and/or elicit protective immunity in animal models. These surface proteins have been implicated in interactions with human epithelial cells, binding to extracellular matrix components, and/or evasion of host immunity. Of note, several S. agalactiae surface proteins are related to surface proteins identified in other bacterial pathogens, emphasizing the general interest of the S. agalactiae proteins. Because some S. agalactiae surface proteins elicit protective immunity, they hold promise as components in a vaccine based only on proteins or as carriers in polysaccharide conjugate vaccines.

Molecular pathogenesis of neonatal group B streptococcal infection: no longer in its infancy

The process of human infection by group B Streptococcus (GBS) is complex and multifactorial. While this bacterium has adapted well to asymptomatic colonization of adult humans, it remains a potentially devastating pathogen to susceptible infants. Advances in molecular techniques and refinement of in vitro and in vivo model systems have elucidated key elements of the pathogenic process, from initial attachment to the maternal vaginal epithelium to penetration of the newborn blood-brain barrier. Sequencing of two complete GBS genomes has provided additional context for interpretation of experimental data and comparison to other well-studied pathogens. Here we review recent discoveries regarding GBS virulence mechanisms, many of which are revealed or magnified by the unique circumstances of the birthing process and the deficiencies of neonatal immune defence. Appreciation of the formidable array of GBS virulence factors underscores why this bacterium remains at the forefront of neonatal pathogens.

The fibrinogen receptor FbsA promotes adherence of Streptococcus agalactiae to human epithelial cells

Streptococcus agalactiae is a major cause of bacterial pneumonia, sepsis, and meningitis in human neonates. During the course of infection, S. agalactiae adheres to a variety of epithelial cells but the underlying mechanisms are only poorly understood. The present report demonstrates the importance of the fibrinogen receptor FbsA for the streptococcal adherence and invasion of epithelial cells. Deletion of the fbsA gene in various S. agalactiae strains substantially reduced their binding of soluble fibrinogen and their adherence to and invasion of epithelial cells, indicating a role of FbsA in these different processes. The adherence and invasiveness of an fbsA deletion mutant were partially restored by reintroducing the fbsA gene on an expression vector. Heterologous expression of fbsA in Lactococcus lactis enabled this bacterium to adhere to but not to invade epithelial cells, suggesting that FbsA is a streptococcal adhesin. Flow cytometry experiments revealed a dose-dependent binding of FbsA to the surface of epithelial cells. Furthermore, tissue culture experiments exhibited an intimate contact of FbsA-coated latex beads with the surfaces of human epithelial cells. Finally, host cell adherence and invasion were significantly blocked in competition experiments with either purified FbsA protein or a monoclonal antibody directed against the fibrinogen-binding epitope of FbsA. Taken together, our studies demonstrate that FbsA promotes the adherence of S. agalactiae to epithelial cells but that FbsA does not mediate the bacterial invasion into host cells. Our results also indicate that fibrinogen-binding epitopes within FbsA are involved in the adherence of S. agalactiae to epithelial cells.

The novel fibrinogen-binding protein FbsB promotes Streptococcus agalactiae invasion into epithelial cells

Streptococcus agalactiae is a major cause of bacterial sepsis and meningitis in human newborns. The interaction of S. agalactiae with host proteins and the entry into host cells thereby represent important virulence traits of these bacteria. The present report describes the identification of the fbsB gene, encoding a novel fibrinogen-binding protein that plays a crucial role in the invasion of S. agalactiae into human cells. In Western blots and enzyme-linked immunosorbent assay (ELISA) experiments, the FbsB protein was demonstrated to interact with soluble and immobilized fibrinogen. Binding studies showed the N-terminal 388 residues of FbsB and the Aalpha-subunit of human fibrinogen to recognize each other. By reverse transcription (RT)-PCR, the fbsB gene was shown to be cotranscribed with the gbs0851 gene in S. agalactiae. Deletion of the fbsB gene in the genome of S. agalactiae did not influence the binding of the bacteria to fibrinogen, suggesting that FbsB does not participate in the attachment of S. agalactiae to fibrinogen. In tissue culture experiments, however, the fbsB deletion mutant was severely impaired in its invasion into lung epithelial cells. Bacterial invasion could be reestablished by introducing the fbsB gene on a shuttle plasmid into the fbsB deletion mutant. Furthermore, treatment of lung epithelial cells with FbsB fusion protein blocked S. agalactiae invasion of epithelial cells in a dose-dependent fashion. These results suggest an important role of the FbsB protein in the overall process of host cell entry by S. agalactiae.

Translocation of Enterococcus faecalis strains across a monolayer of polarized human enterocyte-like T84 cells

We used a two-chamber system to study transcytosis of Enterococcus faecalis across monolayers of human colon carcinoma-derived T84 cells, which show structural resemblance to the native intestine. Among 16 E. faecalis isolates from different sources, the well-characterized strain OG1RF and 8 other isolates (2 endocarditis isolates, 1 urine isolate, and all 5 fecal isolates) showed translocation in this assay, while 6 clinical isolates (3 endocarditis and 3 urine isolates), the recipient strain JH2-2, and the control, Escherichia coli DH5alpha, had no detectable translocation. Of two OG1RF mutants involving the previously studied epa (enterococcal polysaccharide antigen) gene cluster, known to be needed for virulence and resistance to killing by polymorphonuclear leukocytes, one epa mutant (TX5179) was unable to translocate, while TX5180, with an epa disruption farther downstream, showed a moderate decrease in translocation relative to that of the wild-type strain OG1RF (P < 0.01), indicating that the epa gene cluster is important for translocation across a T84 monolayer. This observation was confirmed by complementation of the epa mutant (TX5179) with epa genes and restoration of its translocation ability. In conclusion, we have demonstrated translocation of at least some strains of E. faecalis across T84 monolayers, although strains differ considerably in this ability, and we have demonstrated that epa mutations can cause marked changes in successful translocation. These results suggest that this model may be a useful in vitro system for studying the process of translocation from the intestinal tract.

Alpha C protein of group B Streptococcus binds host cell surface glycosaminoglycan and enters cells by an actin-dependent mechanism

Group B Streptococcus (GBS) colonizes mucosal surfaces of the human gastrointestinal and gynecological tracts and causes disease in a wide range of patients. Invasive illness occurs after organisms traverse an epithelial boundary and enter deeper tissues. Previously we have reported that the alpha C protein (ACP) on the surface of GBS mediates GBS entry into ME180 cervical epithelial cells and GBS translocation across layers of these cells. We now demonstrate that ACP interacts with host cell glycosaminoglycan (GAG); the interaction of ACP with ME180 cells is inhibited if cells are pretreated with sodium chlorate, an inhibitor of sulfate incorporation, or with heparitinases. The interaction is also inhibited in the presence of soluble heparin or heparan sulfate or host cell-derived GAG. In addition, ACP binds soluble heparin specifically in inhibition and dot blot assays. After interaction with host GAG, soluble ACP enters ME180 cells and fractionates to the eukaryotic cell cytosol. These events are inhibited in cells pretreated with cytochalasin D or with Clostridium difficile toxin B. These data indicate that full-length ACP interacts with ME180 cell GAG and enters the eukaryotic cell cytosol by a mechanism that involves Rho GTPase-dependent actin rearrangements. We suggest that these molecular interactions drive ACP-mediated translocation of GBS across epithelial barriers, thereby facilitating invasive GBS infection.

Oxygen regulates invasiveness and virulence of group B streptococcus

The facultative anaerobe group B Streptococcus (GBS) is an opportunistic pathogen of pregnant women, newborns, and the elderly. Although several virulence factors have been identified, environmental factors that regulate the pathogenicity of GBS have not been well characterized. Using the dynamic in vitro attachment and invasion system (DIVAS), we examined the effect of oxygen on the ability of GBS to invade immortalized human epithelial cells. GBS type III strain M781 invaded human epithelial cells of primitive neurons, the cervix, the vagina, and the endometrium in 5- to 400-fold higher numbers when cultured at a cell mass doubling time (t(d)) of 1.8 h than at a slower t(d) of 11 h. Invasion was optimal when GBS was cultured at a t(d) of 1.8 h in the presence of >or=5% oxygen and was significantly reduced without oxygen. Moreover, GBS grown in a chemostat under highly invasive conditions (t(d) of 1.8 h, with oxygen) was more virulent in neonatal mice than was GBS grown under suboptimal invasion conditions (t(d) of 1.8 h, without oxygen), suggesting a positive association between in vitro invasiveness with DIVAS and virulence.

Group B streptococcus: prevention of early-onset neonatal sepsis

Group B streptococcus (GBS) was recognized as a major pathogen of neonatal disease in the 1970s. With a case-fatality rate of 5% to 20%, prevention of GBS neonatal disease has been an ongoing concern. The Centers for Disease Control and Prevention (CDC), and American College of Obstetricians and Gynecologists (ACOG) published guidelines for preventive strategies in 1996. These strategies, either a risk-based or a culture-based program, have been responsible for reduced incidence of GBS-newborn disease from 1.7 to 0.4 per 1,000 live births in the years 1993 to 1999. However, there has been considerable variability in practice patterns. Reanalysis now shows that a culture-based prevention strategy provides greater reduction in early-onset neonatal disease than a risk-based protocol. The CDC replacement guidelines of August 2002 recommend culture-based GBS prevention; the risk-based strategy is no longer supported. Continued efforts to eradicate GBS-newborn disease require an understanding of the pathogen, colonization, and transmission, GBS sampling and detection methods, and maternal therapy. Until a reliable vaccination against GBS is developed, prevention of neonatal GBS disease will rely upon intrapartum treatment of maternal carriers.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians

LEARNING OBJECTIVES

After completion of this article, the reader will be able to define the pathogen, describe the methods of transmission and detection, and outline the current recommendations for maternal group B streptococcus therapy.

The alpha C protein mediates internalization of group B Streptococcus within human cervical epithelial cells

Group B Streptococcus (GBS) is the leading cause of bacterial chorioamnionitis and neonatal pneumonia, sepsis, and meningitis. Deletion of the alpha C protein gene (bca) attenuates the virulence of GBS in an animal model; significant survival differences in the first 24 h of infection suggest a pathogenic role for the alpha C protein early in the infection process. We examined the role of alpha C protein in the association between GBS and mucosal surfaces using a human cervical epithelial cell line, ME180. Fluorescent and confocal microscopy and flow cytometry demonstrated that 9-repeat alpha C protein binds to the surface of ME180 cells. Isolated N-terminal region of this protein also binds to these cells and competitively inhibits binding of the full protein. Wild-type GBS strain A909 and the bca-null isogenic mutant JL2053 bound similarly to the surface of ME180 cells. However, A909 entered these cells threefold more. Internalization of A909 was inhibited with 2- and 9-repeat alpha C and with N-terminal region alone but not by repeat region-specific peptide. Translocation across polarized ME180 membranes was fivefold greater for A909 than for JL2053. These findings suggest a role for the alpha C protein in interaction with epithelial surfaces and initiation of infection.

The group B streptococcal C5a peptidase is both a specific protease and an invasin

The group B streptococcus (GBS) is a major cause of pneumonia, sepsis, and meningitis in neonates and a serious cause of mortality or morbidity in immunocompromised adults. Although these streptococci adhere efficiently and invade a variety of tissue-specific epithelial and endothelial cells, adhesins and invasins are still unknown. All serotypes of GBS studied to date express C5a peptidase (SCPB) on their surface. This investigation addresses the possibility that this relatively large surface protein has additional activities. Rabbit anti-SCPB serum inhibited invasion of lung epithelial A549 cells by the serotype Ia strain O90R, suggesting that SCPB is an invasin. This was confirmed by inserting an in-frame 25-amino-acid deletion into the scpB gene. Invasion of HEp2 and A549 human cell lines was significantly reduced by the mutation. Enzyme-linked immunosorbent assays were used to demonstrate that purified SCPB protein binds directly to HEp2 and A549 cells and also binds the extracellular matrix protein fibronectin. Binding was dose dependent and saturable. These results suggested that SCPB is one of several potential invasins essential for GBS colonization of damaged epithelium.

Endotoxin-neutralizing antimicrobial proteins of the human placenta

Microbial colonization and infection of placental tissues often lead to adverse pregnancy outcomes such as preterm birth, a leading cause of neonatal morbidity and mortality. The fetal membranes of the placenta, a physical and active barrier to microbial invasion, encapsulate the fetus and secure its intrauterine environment. To examine the innate defense system of the human placenta, antimicrobial peptides were isolated from the fetal membranes of human placenta and characterized biochemically. Two salt-resistant antimicrobial host proteins were purified to homogeneity using heparin-affinity and reversed-phase HPLC. Characterization of these proteins revealed that they are identical to histones H2A and H2B. Histones H2A and H2B showed dose-dependent inhibition of the endotoxin activity of LPS and inhibited this activity by binding to and therefore blocking both the core and lipid A moieties of LPS. Consistent with a role for histones in the establishment of placental innate defense, histones H2A and H2B were highly expressed in the cytoplasm of syncytiotrophoblasts and amnion cells, where the histone proteins were localized mainly to the epithelial surface. Furthermore, culturing of amnion-derived WISH cells led to the constitutive release of histone H2B, and histones H2A and H2B contribute to bactericidal activity of amniotic fluid. Our studies suggest that histones H2A and H2B may endow the epithelium of the placenta with an antimicrobial and endotoxin-neutralizing barrier against microorganisms that invade this immune-privileged site.

Definition of a type of abnormal vaginal flora that is distinct from bacterial vaginosis: aerobic vaginitis

OBJECTIVE

To define an entity of abnormal vaginal flora: aerobic vaginitis.

DESIGN

Observational study.

SETTING

University Hospital Gasthuisberg, Leuven, Belgium.

SAMPLE

631 women attending for routine prenatal care or attending vaginitis clinic.

METHODS

Samples were taken for fresh wet mount microscopy of vaginal fluid, vaginal cultures and measurement of lactate, succinate and cytokine levels in vaginal fluid. Smears deficient in lactobacilli and positive for clue cells were considered to indicate a diagnosis of bacterial vaginosis. Aerobic vaginitis was diagnosed if smears were deficient in lactobacilli, positive for cocci or coarse bacilli, positive for parabasal epithelial cells, and/or positive for vaginal leucocytes (plus their granular aspect).

RESULTS

Genital complaints include red inflammation, yellow discharge, vaginal dyspareunia. Group B streptococci, escherichia coli, staphylococcus aureus and trichomonas vaginalis are frequently cultured. Vaginal lactate concentration is severely depressed in women with aerobic vaginitis, as in bacterial vaginosis, but vaginal succinate is not produced. Also in contrast to bacterial vaginosis, aerobic vaginitis produces a host immune response that leads to high production of interleukin-6, interleukin-1-beta and leukaemia inhibitory factor in the vaginal fluid.

CONCLUSION

Aerobic vaginitis is associated with aerobic micro-organisms, mainly group B streptococci and E. coli. Its characteristics are different from those of bacterial vaginosis and elicit an important host response. The most severe form of aerobic vaginitis equals desquamative inflammatory vaginitis. In theory, aerobic vaginitis may be a better candidate than bacterial vaginosis as the cause of pregnancy complications, such as ascending chorioamnionitis, preterm rupture of the membranes and preterm delivery.

An immune hypothesis of sexual orientation

Sexual orientation is encoded within immune-cell subsets (ICS) of mucosal and epithelial tissues. Gender orientation may be encoded within other ICS. Many immune cells: recognize and react to H-Y and H-X antigens; and enact these perceptions and reactions in accord with the perceiver's and the perceived's MHC haplotype, XX or XY status, and immune-self recognition. Non-heterosexual orientations derive from excessive cross-priming, accompanied by clonal deletions, clonal expansions, anergy and tolerance. For at least some tissues, cross-priming sufficient to induce altered orientations may occur during critical periods of immunological development and can occur during fetal and infant development via maternal-fetal transfusion, placental pathology, and impaired maternal nutrient-status or via excessive peripheral apoptosis during postnatal illness. Mast cell interactions with neurons illustrate how mucosal perceptions can be transduced into neuronal signals that modulate CNS events. This hypothesis is testable by mixed-lymphocyte reactions in appropriate cell subsets. Dendritic-cell immunizations are a potential therapy.