Progress toward a group B streptococcal vaccine

Recombinant lactococcal-based oral vaccine for protection against Streptococcus agalactiae infections in tilapia (Oreochromis niloticus)

Streptococcosis outbreaks caused by Streptococcus agalactiae infection in tilapia aquaculture have been consistently reported and associated with high mortality and morbidity leading to significant economic losses. Existing vaccine candidates against Streptococcus spp. are designed for intraperitoneal injections that are not practical and labor-intensive which have prompted farmers to protect aquatic animals with antibiotics, thus encouraging the emergence of multidrug resistant bacteria. In this study, a live recombinant L. lactis vaccine expressing a 1403 bp surface immunogenic protein (SIP) and a 1100 bp truncated SIP (tSIP) gene was developed and evaluated against S. agalactiae infection in tilapia. Both SIP and tSIP sequences were cloned and transformed into L. lactis. The recombinant L.lactis vaccine was orally administered to juvenile tilapia for a month. Detection of SIP-specific serum IgM in vaccinated groups compared to control groups indicated that recombinant proteins expressed from L. lactis could elicit immunogenic reactions in tilapia. Fish immunized with the tSIP vaccine also showed the highest level of protection compared to other test groups, and the mortality rate was significantly reduced compared to both control groups. The relative percentage of survival (RPS) against S. agalactiae for both SIP and tSIP-vaccinated groups was 50 % and 89 %, respectively, at 14 days post-challenge. Significant up-regulation of IgM, IL-1β, IL-10, TNF-α and IFN-γ were observed at day 34 between the vaccinated and control groups. These results indicated that the recombinant lactococcal tSIP vaccine can elicit both cell-mediated and humoral responses and is recommended as a potential oral vaccine against S. agalactiae infection. Future work will include further in vivo challenge assessments of this vaccine candidate fused with adjuvants to boost immunogenicity levels in tilapia.

Genomics-driven prophylactic measures to increase streptococcosis resistance in tilapia

Streptococcosis caused by Streptococcus agalactiae and S. iniae is a significant problem that affects the success of tilapia aquaculture industries worldwide. In this critical review, we summarize the applicable practical strategies which may effectively enhance the world tilapia aquaculture development. Recently, the effect of vaccination and selective breeding programmes has been recognized as valuable tools to control the target disease and other consequent negative impacts caused by chemical and drug application. Advances in sequencing and molecular technologies are vital helpful factors with which to develop robust vaccines and increase the selective breeding programme's precision against streptococcosis. The genomic selection for streptococcosis-resistant tilapia strains and crucial genomic application for genomics' contribution to the development of novel Streptococcus vaccine, comparative genomics approach identifying vaccine candidates by reverse vaccinology, and next-generation vaccine design were described. Information from our review is encouraging for practical implementation of the development of vaccination and genomic selection in tilapia for streptococcosis resistance, which may be vital factors to sustain the world tilapia aquaculture industry effectively.

Calibration of a serum reference standard for Group B streptococcal polysaccharide conjugate vaccine development using surface plasmon resonance

Group B streptococcus (GBS) is a leading cause of neonatal morbidity and mortality worldwide. Development of a maternal vaccine to protect newborns through placentally transferred antibody is considered feasible based on the well-established relationship between anti-GBS capsular polysaccharide (CPS) IgG levels at birth and reduced risk of neonatal invasive GBS. An accurately calibrated serum reference standard that can be used to measure anti-CPS concentrations is critical for estimation of protective antibody levels across serotypes and potential vaccine performance. For this, precise weight-based measurement of anti-CPS IgG in sera is required. Here, we report an improved approach for determining serum anti-CPS IgG levels using surface plasmon resonance with monoclonal antibody standards, coupled with a direct Luminex-based immunoassay. This technique was used to quantify serotype-specific anti-CPS IgG levels in a human serum reference pool derived from subjects immunized with an investigational six-valent GBS glycoconjugate vaccine.

Serotype Distribution, Virulence Determinants and Antimicrobial Susceptibility of Streptococcus agalactiae Isolated from Young Infants

Background: Streptococcus agalactiae (Group B Streptococcus, GBS) is the most common cause of serious infections in the first 3 months of life worldwide. The pathogenicity of GBS is closely related to serotypes, surface proteins and virulence factors, and the distribution of them may vary temporally and geographically. However, data related to GBS surface proteins and virulence determinants in China are very few. The aim of this study is to investigate the genetic characteristics of clinical GBS isolates from infected infants. Methods: We recovered GBS isolates from infected infants younger than 3 months during 2017−2021 at Maternal and Child Health Hospital of Hubei Province in China. We assessed the GBS serotypes, surface proteins, virulence determinants and antibiotic resistance genes distribution, by Multilocus sequence typing (MLST) and whole-genome sequencing analysis. Results: Among 97 isolates (81 EOD and 16 LOD), 5 serotypes were detected. Serotype III was the most represented (49.5%), followed by type Ib (20.6%). The isolates belonged to 17 different sequence types (STs) that grouped into the 8 clonal complexes (CCs). The most frequently identified ST was ST17 (23.7%). The most predominant surface protein of alpha-protein-like (alp) family (one of the protein components of the GBS surface antigen, resistant to trypsin) present was Rib (41.2%), which was mainly detected in serotype III. The srr1, which encodes Srr1 protein, was identified in 54.6% of isolates. The hvgA encoding for hypervirulent GBS adhesin can be detected in all 24 serotype III GBS. Among the pilus islands genes, 50% and 58.8% of the isolates were positive for pi-1 and pi-2a genes, respectively. The presence of pi-2b was mainly associated with serotype III/CC17 strains; 56.7% of isolates carried tetM, tetO/tetL, ermB antibiotic resistant genes. Among all the virulence genes detected, the cfb-cylE-lmb-pavA pattern was the main virulence gene profile (81.4%), mainly in serotype III/CC17. Conclusions: The whole genomic sequencing data revealed the high variation in surface proteins, determining virulence and antibiotic resistance in clinical isolates from 97 GBS infected infants. These data provide insightful characteristics of genetic features of GBS. Constant epidemiological surveillance is warranted to provide information on the GBS pathogenic dynamics and antibiotic resistance profiles in the surveyed areas for improving therapeutic outcomes.

Identifying large-scale recombination and capsular switching events in Streptococcus agalactiae strains causing disease in adults in the UK between 2014 and 2015

Cases of invasive group B streptococcal infection in the adult UK population have steadily increased over recent years, with the most common serotypes being V, III and Ia, but less is known of the genetic background of these strains. We have carried out in-depth analysis of the whole-genome sequences of 193 clinically important group B Streptococcus (GBS) isolates (184 were from invasive infection, 8 were from non-invasive infection and 1 had no information on isolation site) isolated from adults and submitted to the National Reference Laboratory at the UK Health Security Agency between January 2014 and December 2015. We have determined that capsular serotypes III (26.9%), Ia (26.4%) and V (15.0%) were most commonly identified, with slight differences in gender and age distribution. Most isolates (n=182) grouped to five clonal complexes (CCs), CC1, CC8/CC10, CC17, CC19 and CC23, with common associations between specific serotypes and virulence genes. Additionally, we have identified large recombination events mediating potential capsular switching events between sequence type (ST)1 serotype V and serotypes Ib (n=2 isolates), II (n=2 isolates) and VI (n=2 isolates); between ST19 serotype III and serotype V (n=5 isolates); and between CC17 serotype III and serotype IV (n=1 isolate). The high genetic diversity of disease-causing isolates and multiple recombination events reported in this study highlight the need for routine surveillance of the circulating disease-causing GBS strains. This information is crucial to better understand the global spread of GBS serotypes and genotypes, and will form the baseline information for any future GBS vaccine research in the UK and worldwide.

Determination of Capsular Serotypes, Antibiotic Susceptibility Pattern, and Molecular Mechanism of Erythromycin Resistance among Clinical Isolates of Group B Streptococcus in Isfahan, Iran

Background:

Documented streptococcal resistance to erythromycin has recently been raised. The aim of this study is to identify the molecular mechanism of erythromycin resistance among group B Streptococcus (GBS) strains and to correlate with the clinical origin of strains.

Materials and Methods:

A total number of 134 colonizing (n = 36), invasive (n = 36), noninvasive (n = 46), and asymptomatic (n = 16) GBS isolates were characterized by the detection of dltS gene, capsular serotyping, antibiotic susceptibility profiles using disc diffusion method, and screening of the ermB, ermTR, and mefA resistance genes.

Results:

The distribution of capsular serotypes was as follow: serotype III (24.6%), Ia (21.6%), V (17.9%), Ib (14.9%), II (8.9%), IV (8.9%), VI (1.5%), and VII (1.5%). From 134 GBS isolates, 51 (38%) isolates were resistant to erythromycin. The constitutive macrolide lincosamide streptogrmin B (MLSB) was the most common resistance phenotype (62.7%), followed by inducible MLSB (27.4%) and M phenotype (9.8%). Erythromycin resistance rate was higher among asymptomatic GBS strains (13/16, 81.2%). Serotype III was the most prevalent type among resistant isolates (41.1%). The ermB gene highly distributed among resistant strains (64.7%), followed by ermTR (21.5%) and mefA (9.8%). The ermB gene was related to constitutive MLSB phenotype (84.3%, P < 0.05) and serotypes III (61.9%), Ib (87.5%), and V (83.3%). All M phenotype strains harbored mefA gene and were in association with serotype Ia (90%).

Conclusion:

The current study suggests that ribosomal modification with erm genes is the main mechanism of erythromycin resistance. Because of relatively high prevalence of erythromycin resistance, double disc test highly recommended for GBS disease treatment and intrapartum prophylaxis among penicillin intolerant patients in our region.

Defeating meningitis by 2030 - an ambitious target

Acute bacterial meningitis remains a major cause of mortality and morbidity, especially in lower-income countries. Thus, in 2017, a group of people concerned with this continuing problem came together to plan a way forward. A task force was established, a baseline situation analysis undertaken and a road map for a new initiative ‘Defeating Meningitis by 2030’ prepared. This road map will be launched officially in September 2021. Additional finances for meningitis control will be needed, together with the support of many different institutions and people with different skills, if the ‘Defeating Meningitis by 2030’ initiative is to achieve its ambitious goals.

Molecular Characteristics of IS1216 Carrying Multidrug Resistance Gene Cluster in Serotype III/Sequence Type 19 Group B Streptococcus

Streptococcus agalactiae is the leading cause of meningitis in newborns and a significant cause of invasive diseases in pregnant women and adults with underlying diseases. Antibiotic resistance against erythromycin and clindamycin in group B streptococcus (GBS) isolates has been increasing worldwide. GBS expresses the Srr1 and Srr2 proteins, which have important roles in bacterial infection. They have been investigated as novel vaccine candidates against GBS infection, with promising results. But a recent study detected non-srr1/2-expressing clinical isolates belonging to serotype III. Thus, we aimed to analyze the genotypes of non-srr1/2 GBS clinical isolates collected between 2013 and 2016 in South Korea. Forty-one (13.4%) of the 305 serotype III isolates were identified as non-srr1/2 strains, including sequence type 19 (ST19) (n = 16) and ST27 (n = 18) strains. The results of the comparative genomic analysis of the ST19/serotype III/non-srr1/2 strains further revealed four unique gene clusters. Site 4 in the srr1 gene locus was replaced by an lsa(E)-lnu(B)-aadK-aac-aph-aadE-carrying multidrug-resistant gene cluster flanked by two IS1216 transposases with 99% homology to the enterococcal plasmid pKUB3007-1. Despite the Srr1 and Srr2 deficiencies, which resulted in reduced fibrinogen binding, the adherence of non-srr1/2 strains to endothelial and epithelial cells was comparable to that of Srr1- or Srr2-expressing strains. Moreover, their virulence in mouse models of meningitis was not significantly affected. Furthermore, additional adhesin-encoding genes, including a gene encoding a BspA-like protein, which may contribute to colonization by non-srr1/2 strains, were identified via whole-genome analysis. Thus, our study provides important findings that can aid in the development of vaccines and antibiotics against GBS. IMPORTANCE Most previously isolated group B streptococcus (GBS) strains express either the Srr1 or Srr2 glycoprotein, which plays an important role in bacterial colonization and invasion. These glycoproteins are potential protein vaccine candidates. In this study, we first report GBS clinical isolates in which the srr1/2 gene was deleted or replaced with foreign genes. Despite Srr1/2 deficiency, in vitro adherence to mammalian cells and in vivo virulence in murine models were not affected, suggesting that the isolates might have another adherence mechanism that enhanced their virulence aside from Srr1/2-fibrinogen-mediated adherence. In addition, several non-srr1/2 isolates replaced the srr1/2 gene with the lnu(B) and lsa(E) antibiotic resistance genes flanked by IS1216, effectively causing multidrug resistance. Collectively, we believe that our study identifies the underlying genes responsible for the pathogenesis of new GBS serotype III. Furthermore, our study emphasizes the need for alternative antibiotics for patients who are allergic to β-lactams and for those who are pregnant.

Development and Validation of Enzyme-Linked Immunosorbent Assay for Group B Streptococcal Polysaccharide Vaccine

Streptococcus agalactiae (group B Streptococcus, GBS) is a leading cause of neonatal sepsis and meningitis in infants. Limitations of prenatal GBS screening and intrapartum antibiotic prophylaxis render developing GBS vaccines a high priority. In this study, we developed an enzyme-linked immunosorbent assay (ELISA) for the practical and large-scale evaluation of GBS capsular polysaccharide (PS) vaccine immunogenicity against three main serotypes, Ia, III, and V. GBS-ELISA was developed and subsequently validated using a standardized curve-fitting four-parameter logistic method. Specificity was measured using adsorption of serum with homologous and heterologous PS. Homologous adsorption showed a ≥75% inhibition of all three serotypes, whereas with heterologous PS, IgG GBS-ELISA inhibited only ≤25% of serotypes III and V. However, with serotype Ia, IgG antibody levels decreased by >50%, even after adsorption with heterologous PS (III or V). In comparison, the inhibition opsonophagocytic killing assay (OPA) of serotypes Ia GBS exhibited a reduction in opsonophagocytic activity of only 20% and 1.1% for serotypes III and V GBS, respectively. The precision of the GBS-ELISA was assessed in five independent experiments using four serum samples. The coefficient of variation was <5% for all three serotypes. This standardized GBS-ELISA would be useful for GBS vaccine development and its evaluation.

A Narrative Review of the Molecular Epidemiology and Laboratory Surveillance of Vaccine Preventable Bacterial Meningitis Agents: Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae and Streptococcus agalactiae

This narrative review describes the public health importance of four most common bacterial meningitis agents, Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae, and S. agalactiae (group B Streptococcus). Three of them are strict human pathogens that normally colonize the nasopharynx and may invade the blood stream to cause systemic infections and meningitis. S. agalactiae colonizes the genito-gastrointestinal tract and is an important meningitis agent in newborns, but also causes invasive infections in infants or adults. These four bacteria have polysaccharide capsules that protect them against the host complement defense. Currently licensed conjugate vaccines (against S. pneumoniae, H. influenza, and N. meningitidis only but not S. agalactiae) can induce protective serum antibodies in infants as young as two months old offering protection to the most vulnerable groups, and the ability to eliminate carriage of homologous serotype strains in vaccinated subjects lending further protection to those not vaccinated through herd immunity. However, the serotype-specific nature of these vaccines have driven the bacteria to adapt by mechanisms that affect the capsule antigens through either capsule switching or capsule replacement in addition to the possibility of unmasking of strains or serotypes not covered by the vaccines. The post-vaccine molecular epidemiology of vaccine-preventable bacterial meningitis is discussed based on findings obtained with newer genomic laboratory surveillance methods.

Trends in molecular characteristics and antimicrobial resistance of group B streptococci: a multicenter study in Serbia, 2015-2020

Group B Streptococcus (GBS) is a major cause of neonatal morbidity and mortality. Serbia has not fully implemented preventive measures against GBS neonatal diseases. Therefore, we aimed to assess the maternal GBS colonisation and invasive neonatal disease rate, to reveal the trends of antimicrobial resistance and serotype distribution of GBS from various patient groups. Randomly selected non-invasive (n = 991) and all invasive GBS (n = 80) collected throughout Serbia from 2015 to 2020 were tested for antimicrobial susceptibility, capsular typing, and hvgA detection. Overall, 877/5621 (15.6%) pregnant women were colonised with GBS. Invasive GBS infections incidence in infants (0.18/1000 live births) showed a decreasing trend (0.3 to 0.1/1000 live births). Type III was overrepresented in infants with invasive infections (n = 35, 58.3%), whereas type V predominated among colonised adults (n = 224, 25.5%) and those with noninvasive (n = 37, 32.5%) and invasive infections (n = 8, 40%). The hypervirulent clone III/ST17 was highly associated with invasive infections (n = 28, 35%), particularly late-onset disease (n = 9, 47.4%), showing an increase from 12.3 to 14.8%. The GBS resistance to erythromycin and clindamycin was 26.7% and 22.1%, respectively, with an upward trend. The emergence of the hypervirulent clone III/ST17 and the escalation in GBS resistance highlight an urgent need for continuous monitoring of GBS infections.

Systematic review of Group B Streptococcal capsular types, sequence types and surface proteins as potential vaccine candidates

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Most comprehensive review of Group B Streptococcal serotypes through 2018.

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First systematic review of Group B Streptococcal strain type and protein data.

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Theoretically candidate vaccines may protect against 93-99% disease-causing strains.

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More studies on GBS strains in low- and middle-income countries are needed.

Background

21 million pregnant women worldwide (18%) are estimated to carry Group B Streptococcus (GBS), which is a risk for invasive disease in newborns, pregnant women, and stillbirths. Adults ≥ 60 years or with underlying health conditions are also vulnerable to invasive GBS disease. We undertook systematic reviews on GBS organism characteristics including: capsular polysaccharide (serotype), sequence type (multi-locus sequence types (MLST)), and virulence proteins. We synthesised data by at-risk populations, to inform vaccine development.

Methods

We conducted systematic reviews and meta-analyses to estimate proportions of GBS serotypes for at risk populations: maternal colonisation, invasive disease in pregnant women, stillbirths, infants 0–90 days age, and older adults (≥60 years). We considered regional variation and time trends (2001–2018). For these at-risk population groups, we summarised reported MLST and surface proteins.

Results

Based on 198 studies (29247isolates), 93–99% of GBS isolates were serotypes Ia, Ib, II, III, IV and V. Regional variation is likely, but data gaps are apparent, even for maternal colonisation which has most data. Serotype III dominates for infant invasive disease (60%) and GBS-associated stillbirths (41%). ST17 accounted for a high proportion of infant invasive disease (41%; 95%CI: 35–47) and was found almost exclusively in serotype III strains, less present in maternal colonisation (9%; 95%CI:6–13),(4%; 95%CI:0–11) infant colonisation, and adult invasive disease (4%, 95%CI:2–6). Percentages of strains with at least one of alp 1, alp2/3, alpha C or Rib surface protein targets were 87% of maternal colonisation, 97% infant colonisation, 93% infant disease and 99% adult invasive disease. At least one of three pilus islands proteins were reported in all strains.

Discussion

A hexavalent vaccine (serotypes Ia, Ib, II, III, IV and V) might provide comprehensive cover for all at-risk populations. Surveillance of circulating, disease-causing target proteins is useful to inform vaccines not targeting capsular polysaccharide. Addressing data gaps especially by world region and some at-risk populations (notably stillbirths) is fundamental to evidence-based decision-making during vaccine design.

Asymptomatic GBS bacteriuria during antenatal visits: To treat or not to treat?

Inconsistencies persist regarding the efficacy of treating asymptomatic group B Streptococcus bacteriuria in pregnant individuals with colony counts below 10 (100,000) CFU/mL. Despite these discrepancies, treatment still occurs. This article examines the role of screening and treatment, evidence-based guidelines, and practice patterns to provide clarification and resolve local practice disparities.

Global Perspectives on Immunization During Pregnancy and Priorities for Future Research and Development: An International Consensus Statement

Immunization during pregnancy has been recommended in an increasing number of countries. The aim of this strategy is to protect pregnant women and infants from severe infectious disease, morbidity and mortality and is currently limited to tetanus, inactivated influenza, and pertussis-containing vaccines. There have been recent advancements in the development of vaccines designed primarily for use in pregnant women (respiratory syncytial virus and group B Streptococcus vaccines). Although there is increasing evidence to support vaccination in pregnancy, important gaps in knowledge still exist and need to be addressed by future studies. This collaborative consensus paper provides a review of the current literature on immunization during pregnancy and highlights the gaps in knowledge and a consensus of priorities for future research initiatives, in order to optimize protection for both the mother and the infant.

Preparing to introduce new maternal immunizations in low- and lower-middle-income countries: A report from the Bill & Melinda Gates Foundation convening "Allies in Maternal and Newborn Care"; May 3-4, 2018

New strategies will be critical to reduce infant mortality and severe morbidity - there are still 5.2 million newborn deaths and stillbirths each year. The decline in newborn mortality has not kept pace with the reduction in under-five deaths and is slowest in low- and lower-middle-income countries (LMICs). Maternal immunization is a promising intervention to protect infants when they are most vulnerable - in utero and their first few months of life, before they can receive their own vaccines. Successfully introducing new vaccines for pregnant women in LMICs will require collaboration between two fields - (1) immunization and (2) maternal, newborn and child health - that use different service delivery approaches, operate under different policy and funding paradigms, and are not always integrated. In May 2018, stakeholders from these distinct communities convened to identify challenges and opportunities associated with delivering new maternal immunizations. Participants agreed that antenatal care is a logical platform. However, in many resource-constrained settings, antenatal care providers are already overburdened, and most women do not receive the recommended number of antenatal visits. Implementing maternal immunization could help increase antenatal care attendance by offering an additional safe and effective intervention that women value. Substantial effort is needed to demonstrate the benefits of maternal immunization to decision-makers and providers, and to ensure that countries and health systems are ready for introduction. To that end, participants identified the following priorities: assure coherence of policies for introducing new vaccines for pregnant women and strengthen maternal health interventions; generate demand for existing, recommended, and new maternal vaccines; conduct socio-behavioral, health systems and implementation research to shape optimal vaccine delivery strategies; and strengthen antenatal and perinatal care quality. To achieve these aims, collaboration across fields will be essential. Given that new maternal vaccines are advancing in clinical development, time is of the essence.

Prevalence and capsular type distribution of group B Streptococcus isolated from vagina of pregnant women in Nghe An province, Vietnam

BACKGROUND AND OBJECTIVES

Identification of GBS serotypes provides helpful information for appropriate the development of suitable vaccines; however, no reports from Vietnam have been published. This study has been performed to find the prevalence and serotypes of group B Streptococcus isolated from vagina of pregnant women in Nghe An province, Vietnam.

MATERIALS AND METHODS

Vaginal swabs were collected from pregnant women at 35-37 weeks of gestation at the Nghe An Obstetrics and Pediatrics Hospital, Vietnam between May 2018 and July 2019. The swabs were cultured on 5% sheep blood agar for isolation of GBS. All isolates were identified using the Gram staining, CAMP test and specific PCR. GBS strains were serotyped using the multiplex PCR assays.

RESULTS

The prevalence of vaginal GBS colonization was 9.20% of 750 participants. Among the isolates, serotypes III (39.13%) and V (31.89%) were the most frequent, followed by serotypes Ia (11.59%), VI (11.59%), Ib (2.90%), II (1.45%) and VII (1.45%), respectively. Serotypes IV, VIII and IX were not found.

CONCLUSION

The prevalence of GBS in the Nghe An province of central Vietnam was similar to reports from other parts of the world. The predominat GBS serotypes (III, V, Ia and VI) were slightly different from those previously described from other regions around the world. The high frequency of serotype VI was a notable feature of the strains from pregnant women in Vietnam.

Age-stratified analysis of serotype-specific baseline immunity against group B streptococcus

Group B streptococcus (GBS) vaccines are currently under development. Data on the natural immunity in diverse age groups will aid establishing the GBS immunization policy. In this study, thirty serum samples were collected from three age groups (neonates/infants, pregnant women, and the elderly) between August 2016 and July 2017. Serotype-specific opsonophagocytic activity (OPA) was assessed using a GBS multiplex opsonophagocytic killing assay (MOPA) against serotypes Ia, III, and V. The mean OPA titers for serotype Ia of the three age groups were not significantly different (p = .156), but tended to be lower in neonates/infants (mean ± standard deviation, 137 ± 278). For serotype III and V, the mean OPA titer of neonates/infants (338 ± 623 and 161 ± 445, respectively) was significantly lower than that of pregnant women (1377 ± 1167 and 9414 ± 6394) and the elderly (1350 ± 1741 and 3669 ± 5597) (p = .002). In conclusion, the lower levels of OPA titers against all tested serotypes in neonates/infants, despite high maternal titers, indicates that intrapartum GBS vaccinations may be required for efficient placental transfer of serotype-specific GBS antibodies with high avidity.

The 100 top-cited studies on vaccine: a bibliometric analysis

Objective: The objective of this study was to analyze the 100 most cited studies on vaccine.Methods: A comprehensive search of studies on vaccine was performed in the Web of Science Core Collection without year or language restrictions. The 100 top-cited studies were retrieved after screening abstracts or full-texts. The outcomes of bibliometric analysis included citation time, citation density, journal name, impact factor, publication year, article type, category, open access, and country of origin.Results: The citation times for the 100 top-cited studies ranged from 593 to 2406, with a median citation times of 834. The 100 top-cited studies were published in 32 journals, and the journal with the most studies was New England Journal of Medicine (n = 20). They were published between 1969 and 2012, and 4 authors published at least 2 studies as the first author. The USA contributed the most studies (n = 70), followed by Switzerland (n = 4), England (n = 4) and Finland (n = 4). Eighty-one studies were published as Article, while 19 were Review. Eleven studies were about vaccine for therapeutic and 68 studies were about vaccine for prophylactic.Conclusions: This is the first bibliometric analysis to provide a detailed list of the 100 most-cited studies on vaccine and helps to recognize the quality of the works, discoveries, and trends in the field.

Group B Streptococcus: Trials and Tribulations

Group B Streptococcus (GBS) is estimated to have caused 319,000 cases of neonatal disease resulting in 90,000 infant deaths globally in 2015. It is also associated with maternal sepsis, preterm births, stillbirths and neonatal encephalopathy. There is a significant burden of neurologic impairment among survivors of infant GBS disease. Intrapartum antibiotic prophylaxis strategies have reduced the incidence of newborn early-onset GBS (occurring days 0-6) in some settings, but they are not feasible in many low and middle-income countries. A maternal vaccine given to pregnant women to stimulate passive transplacental transfer of protective antibodies has the potential to reduce maternal disease, adverse pregnancy outcomes and newborn disease. Phase I and II vaccine studies are occurring, but conducting phase III efficacy studies of a GBS vaccine candidate would require very large numbers due to the relatively low incidence of invasive GBS disease. It has therefore been proposed that alternative pathways to vaccine licensure should be explored, for example, through use of a regulatory approved correlate of protection and safety evaluation in mothers, fetuses and infants. These studies would then be followed-up with post-licensure phase IV studies in which vaccine effectiveness is evaluated.

Group B streptococcus prevalence, serotype distribution and colonization dynamics in Western Australian pregnant women

PURPOSE

Streptococcus agalactiae, or group B streptococcus (GBS), is a leading neonatal pathogen that causes sepsis, meningitis and pneumonia. Globally, strategies have been implemented to address vertical transmission, and in Western Australia (WA), culture-based screening at 35-37 weeks' gestation is part of routine care and guides antibiotic administration. Previous Australian studies have focused on other regions or included low sample-size representatives; we aimed to describe antenatal GBS colonization in WA.

METHODOLOGY

A cohort of 814 pregnant women attending antenatal clinics (2015-2017) self-collected vaginal and rectal swabs at ≤22 weeks (n=814) and ≥33 weeks' (n=567) gestation. These were assessed for GBS presence using culture and PCR, and serotyping was conducted using molecular methods. Lifestyle questionnaires and medical data were collected.

RESULTS

We observed an overall GBS colonization rate of 24%, with 10.6  % of positive participants transiently colonized. Ethnicity (Aboriginal, Torres Strait Islander and African), maternal age ≥25 years, vitamin use, frequent sexual intercourse (≥5 times/week) and use of sex toys were associated with GBS colonization. The dominant serotypes identified were Ia (27.9%), III (20.9%), II (16.3%), V (15.8%), Ib (8.4%), VI (5.1%), IV (2.8%), NT (1.9), VIII (0.5%) and IX (0.5%) at visit one, with V (18.9%) preceding serotype II (18.2%) at visit two. Serotype VII was not detected.

CONCLUSION

This is the first cohort study to assess GBS colonization in Western Australian pregnant women and will be highly beneficial for guiding clinical practice and future therapeutic options, in particular, the selection of suitable vaccine candidates.

Characterization and expression of galectin-3 after Streptococcus agalactiae and Aeromonas hydrophila challenge in GIFT strain Nile tilapia (Oreochromis niloticus)

In mammals, Galectin-3 has been revealed to be widely expressed in immune cells and played important role in immune reactions. However, Galectin-3 is frequently less reported in teleost. In the present study, a molecular characterization and expression analysis of galectin-3 were conducted in GIFT strain Nile tilapia. The full-length cDNA is 1034 bp with 690 bp of protein coding sequences. The result of qRT-PCR showed that the mRNA of galectin-3 was widely expressed in various tissues (heart, liver, spleen, gill, kidney, brain, intestine, skin, muscle, and ovary), and the higher expression was observed in immune-related tissues (liver and spleen). The time-course expression analysis revealed that galectin-3 was significantly up-regulated in intestine (5 h, 50 h, and 7 d), liver (5 h, 50 h, and 7 d), spleen (5 and 50 h), head-kidney (5 and 50 h), gill (5 h and 7 d) after Streptococcus agalactiae challenge, and significantly up-regulated in intestine (18, 24, 36, 72, and 96 h), liver (6, 18, 24, 96 h, and 6 d), spleen (18, 24, 36, 72, and 96 h), head-kidney (6, 12, 18, 24, 36, 72, and 96 h), and gill (12, 18, 24, and 36 h) after Aeromonas hydrophila challenge. Taken together, these data suggest that galectin-3 plays a role in immune responses in Nile tilapia after bacterial challenge.

An increasing trend of neonatal invasive multidrug-resistant group B streptococcus infections in southern China, 2011-2017

Background

A multidrug-resistant (MDR) RR2 gene cluster was identified by whole-genome sequencing in several highly virulent (ST-17) Group B streptococcus (GBS) isolates, which caused neonatal invasive infections in southern China in 2016. Tracing the transmission and distribution of MDR isolates in this area is important for the effective management of future infections. The aim of this study was to obtain longitudinal data of MDR isolates to monitor epidemiological trends of general common isolates in southern China, and provide evidence for future characterization of antimicrobial resistance mechanisms.

Methods

Clinical information and antimicrobial susceptibility of GBS isolates were acquired from electronic information management system databases of the hospital under study between January 2011 and December 2017. To confirm the presence of intact RR2, the tetO, ant6, lnuB, and ant9 genes located upstream, midstream, and downstream of RR2 were detected by PCR and DNA sequencing.

Results

A total of 149 cases of neonatal invasive GBS infection were identified during the period 2011–2017. Among them, 119 cases (79.9%) were caused by MDR isolates, with a general increasing trend over the past 7 years. Further characterization of 11 isolates showed that six isolates causing late-onset disease (LOD) carry the tetO, ant6, and lnuB genes, which are located on RR2. Moreover, lnuB and ant9 consistently co-occurred in GBS isolates, which suggests their close proximity to one another in the RR2 gene cluster.

Conclusion

The MDR GBS is responsible for a large number of neonatal invasive infections and occurs with increasing frequency over time. Particularly, the MDR GBS isolates that cause LOD are more likely to carry the RR2 gene cluster, compared with those that cause early-onset disease. The rise in number of MDR GBS isolates emphasizes the pressing need for continuous surveillance to monitor their antibiotic susceptibility and epidemiology.