Bactericidal Assay Research Articles

Comparing the meningococcal serogroup C immune response elicited by a tetanus toxoid conjugate quadrivalent meningococcal vaccine (MenACYW-TT) versus a quadrivalent or monovalent C tetanus toxoid conjugate meningococcal vaccine in healthy meningococcal vaccine-naïve toddlers: A randomised, controlled trial

ABSTRACT MenACYW-TT (MenQuadfi®) is a quadrivalent meningococcal tetanus toxoid conjugate vaccine licensed in Europe for use in individuals ≥12 months. This study assessed whether serogroup C immune responses with MenACYW-TT were at least non-inferior, or superior, to those of quadrivalent meningococcal ACWY (MCV4-TT; Nimenrix®) and monovalent meningococcal C (MenC-TT; NeisVac-C®) vaccines in toddlers (12–23 months). In this modified, double-blind Phase III study (NCT03890367), 701 toddlers received one dose of MenACYW-TT (n = 230), MCV4-TT (n = 232) or MenC-TT (n = 239). Serum bactericidal assays with human (hSBA) and baby rabbit (rSBA) complement were used to measure anti-meningococcal serogroup C antibodies at baseline and 30 days post-vaccination. A sequential statistical approach was used for primary and secondary objectives. For the primary objectives, superiority of serogroup C was assessed in terms of hSBA seroprotection rates (defined as titers ≥1:8) and GMTs for MenACYW-TT compared to MCV4-TT, and rSBA GMTs compared to MenC-TT. The safety of all vaccines within 30 days post-vaccination was described. When administered as a single dose to meningococcal vaccine-naïve healthy toddlers the superiority of the MenACYW-TT serogroup C immune response versus MCV4-TT was demonstrated for hSBA GMTs (ratio 16.3 [12.7–21.0]) and seroprotection (difference 10.43% [5.68–16.20]); and versus MenC-TT in terms of rSBA GMTs (ratio 1.32 [1.06–1.64]). The safety profiles of a single dose of MenACYW-TT, MCV4-TT and MenC-TT were similar. In meningococcal vaccine-naïve toddlers, MenACYW-TT induced superior immune responses to serogroup C versus MCV4-TT in terms of hSBA seroprotection and GMTs and versus MenC-TT in terms of rSBA GMTs.

Novel Antibacterial Properties of the Human Dental Pulp Multipotent Mesenchymal Stromal Cell Secretome

It is well recognized that clearance of bacterial infection within the dental pulp precedes pulpal regeneration. However, although the regenerative potential of the human dental pulp has been investigated extensively, its antimicrobial potential remains to be examined in detail. In the current study bactericidal assays were used to demonstrate that the secretome of dental pulp multipotent mesenchymal stromal cells (MSCs) has direct antibacterial activity against the archetypal Gram-positive and Gram-negative bacteria, Staphylococcus aureus and Escherichia coli, respectively, as well as the oral pathogens Streptococcus mutans, Lactobacillus acidophilus, and Fusobacterium nucleatum. Furthermore, a cytokine/growth factor array, enzyme-linked immunosorbent assays, and antibody blocking were used to show that cytokines and growth factors present in the dental pulp MSC secretome, including hepatocyte growth factor, angiopoietin-1, IL-6, and IL-8, contribute to this novel antibacterial activity. This study elucidated a novel and diverse antimicrobial secretome from human dental pulp MSCs, suggesting that these cells contribute to the antibacterial properties of the dental pulp. With this improved understanding of the secretome of dental pulp MSCs and its novel antibacterial activity, new evidence for the ability of the dental pulp to fight infection and restore functional competence is emerging, providing further support for the biological basis of pulpal repair and regeneration.

Silver impregnated bacterial cellulose-chitosan composite hydrogels for antibacterial and catalytic applications

The current study was aimed to develop bacterial cellulose (BC) composites synergistically with polymer (Chitosan (chi)) and a nanomaterial (green synthesized silver nanoparticles (AgNPs) using an Azadirachta indica leaves extract). BC-Chi-Ag composites were developed through ex-situ composite development strategy and evaluated for their structural, biological and catalytic activities. Field emission scanning electron microscopy (FE-SEM) displayed the impregnation of Chi and AgNPs in porous BC network. The composite formulation was further confirmed by the X-ray diffraction (XRD) analysis which showed the presence of additional crystallinic peaks together with pure BC ones. Bactericidal assays of BC-Chi-Ag composites against modern pathogen including Staphylococcus aureus and Escherichia coli depicted significant reduction in growth results compared to pure BC. Kapp value were found to be 0.37081 min−1 and 0.35108 min−1 for catalytic reduction of Rh B and 4-NP, respectively. High bactericidal and catalytic potentials of synthesized BC-Chi-Ag composites seriously justify their potential applications in medical and environmental fields.

Snap-freezing in the Field: Effect of Sample Holding Time on Performance of Bactericidal Assays.

Comparative analyses in biology rely on the quality of available data. Methodological differences among studies may introduce variation in results that obscure patterns. In the field of eco-immunology, functional immune assays such as antimicrobial capacity assays are widely used for among-species applications. Sample storage time and animal handling time can influence assay results in some species, but how sample holding time prior to freezing influences assay results is unknown. Sample holding time can vary widely in field studies on wild animals, prompting the need to understand the implications of such variation on assay results. We investigated the hypothesis that sample holding time prior to freezing influences assay results in six species (Leiocephalus carinatus, Iguana iguana, Loxodonta africana, Ceratotherium simum, Columba livia, and Buteo swainsoni) by comparing antibacterial capacity of serum with varying processing times prior to snap-freezing. Blood was collected once from each individual and aliquots were placed on ice and assigned different holding times (0, 30, 60, 180, and 240 min), after which each sample was centrifuged, then serum was separated and snap-frozen on dry ice and stored at -80ºC for 60 days prior to assaying. For each aliquot, we conducted antibacterial capacity assays with serial dilutions of serum inoculated with E. coli and extracted the dilution at 50% antibacterial capacity for analysis. We found a decrease in antibacterial capacity with increased holding time in one of the six species tested (B. swainsoni), driven in part by complete loss of antibacterial capacity in some individuals at the 240-min time point. While the majority of species' antibacterial capacity were not affected, our results demonstrate the need to conduct pilot assays spanning the anticipated variation in sample holding times to develop appropriate field protocols.

Synthesis and antimicrobial activity of vancomycin–conjugated zinc coordination polymer nanoparticles against methicillin-resistant staphylococcusaureus

Due to the overuse of antimicrobial drugs, Methicillin-resistant Staphylococcus aureus (MRSA) has caused a serious burden worldwide. Herein, we report a novel one-pot hydrothermal route to synthesize a vancomycin-encapsulated Zn-BTC-coordination polymer. FTIR and PXRD confirmed the composites and crystal structure of coordination polymer. The VAC-Zn-BTC-coordination polymer had a mean diameter, polydispersity index (PDI), zeta potential, and encapsulation efficiency of 59.6 ± 2.98 nm, 0.295 ± 0.0147, −11 ±-0.55 mV and 68.24 ± 3.412%, respectively at physiological pH. The safety of MTT in vitro in Human embryonic kidney 293 cells (HEK-293), adenocarcinomic human alveolar basal epithelial cells (A-549), and Michigan Cancer Foundation-7 (MCF-7) cell lines and the hemolytic assay of VAC-Zn-BTC-coordination polymer was evaluated. The in vitro results of the MTT assay were revealed to be safe in all three cell lines and non-hemolytic, thus indicating their biosafety. Molecular dynamics simulations (MDS) showed that higher binding and interaction energies were seen. The VAC release from the VAC-Zn-BTC-coordination polymer was slower than the powder VAC after 48 h. The VAC-Zn-BTC-coordination polymer revealed a lower MIC value of 1.02 μg/mL against MRSA with a 10-fold antimicrobial enhancement. The bactericidal time-kill kinetics assay showed that VAC-Zn-BTC-coordination polymer combinations showed good bactericidal effects over 24 h compared to bare VAC powder. These findings suggest that VAC-Zn-BTC-coordination polymer could be used as excellent potential for the improvement and management of bacterial contagions instigated by MRSA.

Viral vectors expressing group B meningococcal outer membrane proteins induce strong antibody responses but fail to induce functional bactericidal activity

Adenoviral vectored vaccines, with the appropriate gene insert, induce cellular and antibody responses against viruses, parasites and intracellular pathogens such as Mycobacterium tuberculosis. Here we explored their capacity to induce functional antibody responses to meningococcal transmembrane outer membrane proteins. Vectors expressing porin A and ferric enterobactin receptor A antigens were generated, and their immunogenicity assessed in mice using binding and bactericidal assays. The viral vectors expressed the bacterial proteins in an in vitro cell-infection assay and, after immunisation of mice, induced higher titres (>105 end-point titre) and longer lasting (>32 weeks) transgene-specific antibody responses in vivo than did outer membrane vesicles containing the same antigens. However, bactericidal antibodies, which are the primary surrogate of protection against meningococcus, were undetectable, despite different designs to support the presentation of the protective B-cell epitopes. These results demonstrate that, while the transmembrane bacterial proteins expressed by the viral vector induced strong and persistent antigen-specific antibodies, this platform failed to induce bactericidal antibodies. The results suggest that conformation or post-translational modifications of bacterial outer membrane antigens produced in eukaryote cells might not result in presentation of the necessary epitopes for induction of functional antibodies.

Resistome and virulome accretion in an NDM-1-producing ST147 sublineage of Klebsiella pneumoniae associated with an outbreak in Tuscany, Italy: a genotypic and phenotypic characterisation

Carbapenemase-producing Enterobacterales (CPE), particularly those producing metallo-β-lactamases, are among the most challenging antibiotic-resistant pathogens, causing outbreaks of difficult-to-treat nosocomial infections worldwide. Since November 2018, an outbreak of New Delhi metallo-β-lactamases-positive CPE (NDM-CPE) has emerged in Tuscany, Italy. In this study, we aimed to investigate the NDM-CPE associated with the outbreak and characterise the responsible Klebsiella pneumoniae clone. We used whole-genome sequencing and bioinformatic analysis to characterise NDM-CPE isolates that caused bloodstream infections in 53 patients at 11 hospitals in Tuscany and that were collected between Jan 1, 2018, and July 5, 2019 (ie, the early phase of the outbreak and preceding months). The CPE isolates characterised in this study were isolated and identified at the species level and as NDM producers by six diagnostic microbiology laboratories that serve the 11 hospitals. We used comparative genomic analysis, antimicrobial susceptibility testing, plasmid conjugal transfer assays, evaluation of virulence potential in the Galleria mellonella infection model, and serum bactericidal assays to further characterise the clone causing the outbreak. The outbreak was sustained by an ST147 K pneumoniae producing NDM-1, which had a complex resistome that mediated resistance to most antimicrobials (except cefiderocol, the aztreonam-avibactam combination, colistin, and fosfomycin). The clone belonged to a sublineage of probably recent evolution, occurred by the sequential acquisition of an integrative and conjugative element encoding the yersiniabactin siderophore, an FIB(pQil)-type multiresistance plasmid carrying blaNDM-1, and a transferable chimeric plasmid, derived from virulence elements of hypervirulent K pneumoniae, carrying several resistance and virulence determinants. Infection of G mellonella larvae revealed a variable virulence potential. The behaviour in serum bactericidal assays was different from typical hypervirulent K pneumoniae strains, with variable grades of serum resistance apparently associated with mutations in specific chromosomal loci (csrD, pal, and ramR). This description of a sublineage of ST147 K pneumoniae with a complex resistome and virulome that is capable of sustaining a large regional outbreak adds to existing research on the evolutionary trajectories within high-risk clones of K pneumoniae. Global surveillance programmes are warranted to track the dissemination of these lineages, and to prevent and control their spread. Italian Ministry of Health and Department of Experimental and Clinical Medicine, University of Florence.

A Mouse Immunogenicity Model for the Evaluation of Meningococcal Conjugate Vaccines.

The identification of an appropriate animal model for use in the development of meningococcal vaccines has been a challenge as humans are the only natural host for Neisseria meningitidis. Small animal models have been developed and are widely used to study the efficacy or immunogenicity of vaccine formulations generated against various diseases. Here, we describe the development and optimization of a mouse model for assessing the immunogenicity of candidate tetravalent meningococcal polysaccharide (MenACYW-TT) protein conjugate vaccines. Three inbred (BALB/c [H-2d], C3H/HeN [H-2k], or C57BL/6 [H-2b]) and one outbred (ICR [H-2g7]) mouse strains were assessed using serial two-fold dose dilutions (from 2 µg to 0.03125 µg per dose of polysaccharide for each serogroup) of candidate meningococcal conjugate vaccines. Groups of 10 mice received two doses of the candidate vaccine 14 days apart with serum samples obtained 14 days after the last dose for the evaluation of serogroup-specific anti-polysaccharide IgG by ELISA and bactericidal antibody by serum bactericidal assay (SBA). C3H/HeN and ICR mice had a more dose-dependent antibody response to all four serogroups than BALB/c and C57Bl/6 mice. In general, ICR mice had the greatest antibody dose-response range (both anti-polysaccharide IgG and bactericidal antibodies) to all four serogroups and were chosen as the model of choice. The 0.25 µg per serogroup dose was chosen as optimal since this was in the dynamic range of the serogroup-specific dose-response curves in most of the mouse strains evaluated. We demonstrate that the optimized mouse immunogenicity model is sufficiently sensitive to differentiate between conjugated polysaccharides, against unconjugated free polysaccharides and, to degradation of the vaccine formulations. Following optimization, this optimized mouse immunogenicity model has been used to assess the impact of different conjugation chemistries on immunogenicity, and to screen and stratify various candidate meningococcal conjugate vaccines to identify those with the most desirable profile to progress to clinical trials.

Antibacterial activity of Myrtus communis L. and Melaleuca leucadendron var. cajaputi essential oils against antibiotic-resistant bacterial strains

Background: Antimicrobial resistance (AMR) is a global threat to public health. There is a dire need for new antibiotics as AMR threatens our last-resort antibiotics efficacy.1,2 Myrtle plants have been used in folk medicine for centuries. Essential oils from these plants demonstrated therapeutics effects. This study aims to examine the antibacterial activity of essential oils extracted from Myrtus communis L and Melaleuca leucadendron against clinically relevant bacterial pathogens.3Methods: Bacterial growth curves and bactericidal assays were performed on antibiotic-sensitive Staphylococcus aureus (SA) and antibiotic low and high resistant Methicillin-resistant Staphylococcus aureus (MRSA) strains; sensitive and resistant Klebsiella pneumoniae strains (KPS and KPR). Minimum bactericidal concentration (MBC) was performed on 4 strains of colistin sensitive E. coli and 4 colistin resistant E. coli strains. Results: Myrtle essential oils demonstrated a dose-dependent antibacterial activity against all tested strains and inhibited growth even after 24 hours. The tested oils dilutions ranged from 6.15 μl/ml up to 50 μl/ml and inhibited bacterial growth of both antibiotic sensitive and resistant strains of SA, MRSA (Figure 1), and Klebsiella. Further, the incubation of colistin sensitive and colistin-resistant E. coli strains with 50 μl/ml of Myrtle oil for one hour inhibited the growth of all tested strains. The viability of bacteria was tested by spotting on agar plates and further incubation overnight. The data suggest that Myrtle essential oils can effectively kill bacterial pathogens. Conclusion: Essential oils from Myrtus communis L. and Melaleuca leucadendron var. cajaputi possess potent antibacterial activity against antibiotic sensitive and resistant bacterial pathogens. There is a potential for utilizing these antibacterial oils as topical treatment of wound infections.

The role of antibiotic resistance mobile genetic element MCR-1 in enhancing bacterial survival in macrophages

Background: Antimicrobial resistance (AMR) determinants such as mobile colistin resistance (MCR-1) that encodes colistin resistance are increasingly spreading in healthcare-associated and community-acquired infections.1 Colistin, a cationic peptide antibiotic, resistance is encoded by the MCR-1 gene that functions as phosphoethanolamine (PEA) transferase which adds a PEA moiety to lipid A head group rendering it resistant to host antimicrobial cationic peptides (AMPs).2,3 The given hypothesis is that MCR-1 harboring bacteria survive longer in macrophages by evading AMPs. This study aims to investigate the role of MCR-1 in enhancing bacterial survival in macrophages. Methods: Eight E. coli strains were used in the study in which 4 strains were MCR-1 positive and 4 strains were negative. MCR-1 was confirmed by Polymerase Chain Reaction (PCR), and colistin and polymyxin minimal inhibitory concentrations (MICs) were determined using the microdilution method. Macrophage bactericidal assay was employed to examine bacterial survival using adherent murine RAW264 macrophages in an in-vitro bacterial infection model. Briefly, Macrophages were infected with E. coli strains at a multiplicity of infection (MOI) of 50 for 1 hour. The survival of bacteria associated with macrophages was quantified by agar plating method to calculate colony forming units (CFU/ml). Cytokines released from infected macrophages were quantified using ELISA method respectively. Results: Colistin MICs for MCR-1 positive E. coli strains were >25 μg/ml, whereas MCR-1 negative E. coli MICs < 6.2 μg/ml. E. coli strains encoding MCR-1 survived significantly more in association with macrophages (p = 0.024) compared to MCR-1 negative E. coli strains. Further, E.coli strains encoding MCR-1 induced slightly less IL-1β release from infected macrophages compared to E. coli strains without MCR-1 (p = 0.05). Taken together, the data suggest that MCR-1 enhanced bacterial survival in association with macrophages and modulated innate immune responses which may lead to treatment failure. Conclusion: MCR-1 encoding E. coli strains conferred resistance to colistin and survived more in association with macrophages.

Streptococcus gordonii DL1 evades polymorphonuclear leukocyte-mediated killing via resistance to lysozyme.

Streptococcus gordonii is an etiological bacterial agent of infective endocarditis. Although the pathogenesis mechanisms are not well understood, the interaction between streptococci and phagocytes is considered important for the development of infective endocarditis. Previous studies show that some S. gordonii strains, including DL1, survive in polymorphonuclear leukocytes (PMNs), whereas other strains such as SK12 are sensitive to PMN-dependent killing. In this study, we assessed the differences between the sensitivity of S. gordonii DL1 and S. gordonii SK12 to PMN-dependent killing. S. gordonii DL1 showed a higher survival when treated with PMNs than SK12. Both S. gordonii DL1 and S. gordonii SK12 showed high resistance to low pH condition. Compared to S. gordonii SK12, S. gordonii DL1 was sensitive to hydrogen peroxide. However, the resistance of S. gordonii DL1 to the tested bactericidal agents, especially lysozyme, was higher than that of SK12. Furthermore, we performed a bactericidal assay by treating a mixture of S. gordonii DL1 and SK12 with PMNs. S. gordonii DL1 did not enhance the survival of S. gordonii SK12 exposed to PMNs. These results indicated that S. gordonii DL1 is resistant to bactericidal agents that degrade bacteria in phagolysosomes. In addition, there was no secretory factor involved in the resistance to bactericidal agents. The findings of this study may help develop treatments for infective endocarditis caused by S. gordonii.

Effects of Increasing Concentrations of Rifampicin on Different Mycobacterium tuberculosis Lineages in a Whole-Blood Bactericidal Activity Assay.

High-dose rifampicin improved bactericidal activity and culture conversion in early-phase tuberculosis (TB) trials, done mainly in Africa. We performed a whole-blood bactericidal activity (WBA) study to determine whether the effects of high-dose rifampicin differ across globally relevant TB strains and whether effects are similar in dormant bacilli that will be required for enhancing cure. Whole blood from healthy volunteers was spiked with rifampicin (range, 0.63 to 60 mg/L) and incubated with one of four Mycobacterium tuberculosis clinical strains (Haarlem, Latin American-Mediterranean [LAM], East African-Indian [EAI], and Beijing lineages) or a dormant strain (streptomycin-starved 18b [ss18b]). Change in bacterial CFU was estimated after inoculation of WBA cultures in MGIT. WBA increased with higher concentrations of rifampicin in all strains. At rifampicin concentrations up to 5 mg/L, the rates of increase in WBA per unit increase in rifampicin concentration were similar in all 4 clinical strains (P > 0.51). Above 5 mg/L, EAI (P < 0.001) and Beijing (P = 0.007) strains showed greater increases in WBA than did LAM; Haarlem was similar to LAM. The dormant strain showed a lower rate of increase in WBA than clinical strains at rifampicin concentrations up to 5 mg/L; above 5 mg/L, the rate of increase was similar to those in the LAM, Beijing, and Haarlem strains. Increasing rifampicin concentration enhanced WBA in all strains; the greatest effects were seen in strains common in Asia, suggesting that early-phase trial findings may be generalizable beyond Africa. Similar effects of high concentrations of rifampicin on the dormant strain support the concept that this intervention may enhance sterilizing activity.

01. Serum Bactericidal Activity Against Circulating and Reference Strains of Meningococcal Serogroup B in the United States: A Review of Meningococcal Serogroup B (MenB) Vaccines in Adolescents and Young Adults

BackgroundUS adolescents and young adults are at particular risk of invasive meningococcal disease (IMD). In 2018, menincococcal serogroup B was responsible for 36% of IMD cases in the US overall and for 66% of cases in adolescents and young adults. This age group is at high risk of IMD during outbreaks, which result in significant response-related costs. MenB vaccine efficacy against IMD relies on its ability to provide broad protection against diverse disease-causing strains. MenB-FHbp (Trumenba) and MenB-4C (Bexsero) are MenB vaccines licensed in the US as 2-dose series with an interval of 6 mo or 1 mo, respectively, recommended in healthy adolescents and young adults. We review available data on vaccine coverage of serogroup B strains.MethodsA literature review identified relevant information from peer-reviewed publications, congress presentations, and ClinicalTrials.gov. Previously presented but unpublished data from phase 2/3 studies were included.ResultsAfter 2 MenB-FHbp doses, percentages of adolescents and young adults achieving serum bactericidal activity assay using human complement (hSBA) titers ≥1:8 were 79%–99% for 4 heterologous representative test strains and 71%–97% for 10 additional strains, confirming cross-protection against a diverse strain panel (Figure 1; unpublished data). These 14 heterologous strains collectively represent ~80% of disease-causing strains in the US and Europe. In a published study with limited sample size, 44%–78% of subjects had hSBA titers ≥1:8 against strains from 4 US college outbreaks after 2 MenB-FHbp doses. After 2 MenB-4C doses, percentages of 10–25-year-olds achieving hSBA titers ≥1:5 against 3 reference strains homologous to the vaccine antigen were 82%–93% (published data); 15%–100% of adolescents achieved hSBA titers ≥1:4 against a panel of 14 strains (unpublished data). Of college students who received 2 MenB-4C doses, 53%–93% achieved hSBA titers ≥1:4 against 5 US outbreak strains (4/5 strains had antigenic similarity to MenB-4C; published data). ConclusionMenB-FHbp and MenB-4C protect against various serogroup B strains. As for the breadth of coverage provided by these vaccines, available data show that MenB-FHbp elicits robust immune responses to a wide variety of disease-causing strains prevalent in the US (Figure 2). Disclosures Tamera Coyne-Beasley, MD, MPH, Pfizer Inc and GlaxoSmithKline (Advisor or Review Panel member) Joseph Bocchini, MD, Pfizer Inc and Dynavax (Advisor or Review Panel member) Alejandro Cane, M.D., Pfizer Inc (Employee, Shareholder) Cindy Burman, PharmD, Pfizer Inc (Employee, Shareholder) Maria J. Tort, PhD, Pfizer Inc (Employee, Shareholder) Jessica Presa, MD, Pfizer Inc (Employee, Shareholder)

03. Immunogenicity and Safety of a Quadrivalent Meningococcal Conjugate Vaccine (MenACYW-TT) Administered as a Booster Dose in Adults and Adolescents Vaccinated Against Meningococcal Disease 3 - 6 Years Earlier

BackgroundBooster doses of meningococcal conjugate vaccines may induce long-term protection against invasive meningococcal disease. MenACYW-TT [MenQuadfi®] is a quadrivalent meningococcal conjugate vaccine, licensed for use in ages 2 years and older in USA. The vaccine is also licensed in ages 12 months and older in EU and other countries.MethodsA phase IIIb study (NCT04084769) was conducted to evaluate the persistence of immune response in adults and adolescents primed 3-6 years earlier with either MenACYW-TT or MCV4-CRM (Menveo®) and, safety and immunogenicity of MenACYW-TT when administered as a booster dose with or without concomitant administration with MenB vaccines (Bexsero® and Trumenba®). Serum bactericidal assays with human complement (hSBA) and baby rabbit complement (rSBA) were used to measure antibodies against vaccine serogroups at baseline (Day 0 [D0]), D06 (in a subset) and 30 days post-vaccination (D30). Safety data were collected up to 6 months post-vaccination.ResultsAt D0, the GMTs were higher in subjects primed with MenACYW-TT vs MCV4-CRM for serogroups C, Y and W, and were comparable for serogroup A. At D0, all hSBA GMTs were higher than those observed pre-priming dose, suggesting persistence of immunity. Sufficiency of hSBA seroresponse ( >75%) was demonstrated following administration of MenACYW-TT booster dose regardless of the priming vaccine administered 3-6 years earlier. Vaccine seroresponse in a subset of participants at D06 ranged from 77.8% (95%CI 62.9%; 88.8%) for serogroup A to 97.8% (88.5%; 99.9%) for serogroup W suggesting a quick onset of immune response post-booster. Post-vaccination (D30) hSBA GMTs were comparable for serogroups A, Y and W regardless of the nature of the priming vaccine and were higher for serogroup C in subjects primed with MenACYW-TT vaccine. The MenACYW-TT booster dose was well-tolerated and had similar safety profiles regardless of the priming vaccine. The safety profiles were comparable regardless of the MenB vaccine co-administered with MenACYW-TT vaccine.ConclusionMenACYW-TT used as priming vaccine was able to demonstrate persistence of immune response 3-6 years later. MenACYW-TT elicits robust booster responses in adults and adolescents primed with MenACYW-TT or MCV4-CRMDisclosures Betzana Zambrano, MD, Sanofi Pasteur (Employee) Germán Áñez, MD, Sanofi Pasteur (Other Financial or Material Support, Former employee) Sue Jiayuan, MSc, Sanofi Pasteur (Independent Contractor) Judy Pan, PhD, Sanofi Pasteur (Employee) Habiba Arroum, MD, Sanofi Pasteur (Employee) Kucku Varghese, PhD, Sanofi Pasteur (Employee) Emilia Jordanov, MD, Sanofi Pasteur (Employee, Shareholder) Mandeep S. Dhingra, MD, Sanofi Pasteur (Employee, Shareholder)

04. Immunogenicity and Safety of a Quadrivalent Meningococcal Conjugate Vaccine (MenACYW-TT) Administered in Meningococcal Vaccine-Naive Participants Across a Broad Age Range (2-55 Years) in Japan

BackgroundMenACYW-TT [MenQuadfi®] is a quadrivalent meningococcal conjugate vaccine, licensed for use in ages 2 years and older in USA. The vaccine is also licensed in ages 12 months and older in EU and certain other countries. We evaluated the safety and immunogenicity of MenACYW-TT compared to a licensed quadrivalent conjugate meningococcal vaccine (MenACWY-DT [Menactra®]) in Japanese children, adolescents and adults (2-55 years of age).MethodsA phase III modified double-blind, randomized study (NCT04368429) to evaluate the immunogenicity and safety of a single dose of MenACYW-TT versus MenACWY-DT was conducted in 360 participants (ratio 1:1) between ages 2 and 55 years in Japan. Serum bactericidal assays with human complement (hSBA) were used to measure antibodies against vaccine serogroups at baseline (Day 0) and 30 days post-vaccination (D30). Safety data were collected up to 30 days post-vaccination.ResultsNon-inferiority of immune responses for all four serogroups, based on percentages of participants achieving hSBA vaccine seroresponse as primary endpoint, was demonstrated for MenACYW-TT compared to MenACWY-DT at Day 30 in comparison to baseline: 85.6% vs 65.4% for serogroup A, 96.6% vs 62.6% for serogroup C, 87.4% vs 49.2% for serogroup W, and 97.7% vs 63.5% for serogroup Y. The proportions of individuals with hSBA titers ≥ 1:8 following MenACYW-TT administration were higher than those after MenACWY-DT administration for serogroups C (98.9% vs 81.0%), W (99.4% vs 91.1%) and Y (100 % vs 89.4%) and comparable for serogroup A (96.6% vs 92.7%). The hSBA GMTs were higher following administration of MenACYW-TT for all four serogroups. Immunogenicity results in participants 10 to 17 years of age and ≥ 18 years of age were comparable to those in the whole population (2-55 years). The safety profiles of MenACYW-TT and MenACWY-DT were comparable. There were no immediate adverse events (AEs), no AEs leading to study discontinuation, and no vaccine-related serious adverse events reported in the study.ConclusionMenACYW-TT vaccine was well tolerated and demonstrated a non-inferior immune response compared to that for the licensed MenACWY-DT vaccine when administered as a single dose to meningococcal vaccine-naïve children, adolescents, and adults in Japan.Disclosures Osamu Matsuoka, MD, Sanofi Pasteur (Scientific Research Study Investigator, Research Grant or Support) Mugen Ujiie, MD, Sanofi Pasteur (Scientific Research Study Investigator, Research Grant or Support) Hitoshi Kikuchi, MD, Sanofi Pasteur (Scientific Research Study Investigator)Sanofi Pasteur (Research Grant or Support) Danaya Chansinghakul, MD, Sanofi Pasteur (Employee) Takahiro Inoue, MSc, Sanofi Pasteur (Employee) Kucku Varghese, PhD, Sanofi Pasteur (Employee) Nuchra Sirisuphmitr, MSc, Sanofi Pasteur (Employee) Tomoyuki Hashiguchi, MSc, Sanofi Pasteur (Employee) Betzana Zambrano, MD, Sanofi Pasteur (Employee) Takahiro Nakama, MD, Sanofi Pasteur (Employee) Carina Frago, MD, Sanofi Pasteur (Employee, Shareholder) Emilia Jordanov, MD, Sanofi Pasteur (Employee, Shareholder) Mandeep S. Dhingra, MD, Sanofi Pasteur (Employee, Shareholder)

1046. Immunogenicity and Safety of a Quadrivalent Meningococcal Conjugate Vaccine (MenACYW-TT) Administered as a Booster to Adults ≥ 59 Years of Age

Abstract Background MenACYW-TT (MenQuadfi®, Sanofi) is a quadrivalent (serogroups A, C, W, and Y) meningococcal tetanus toxoid conjugate vaccine. It was recently approved for use in persons aged ≥ 2 years in the US and persons aged ≥ 1 year in Europe and certain other countries; trials in infants as young as 6 weeks are ongoing. This study evaluated seroresponse after a MenACYW-TT booster given to adults who received either quadrivalent meningococcal polysaccharide vaccine (MSPV4) or MenACYW-TT three years earlier at age ≥ 56 years. Immune persistence up to 7 years after primary vaccination was also evaluated. Methods This was a Phase 3 randomized, open-label study (NCT04142242) of adults aged ≥ 59 years who participated in previous studies of MenACYW-TT vs MPSV4 (NCT01732627 and NCT02842866). The study was conducted in the US and Puerto Rico. Immune response and persistence were assessed with a serum bactericidal assay using human complement (hSBA). Sufficiency of the vaccine seroresponse was considered demonstrated if the lower limit of the 1-sided 97.5% CI for the percentage of subjects with an hSBA vaccine seroresponse against serogroups A, C, W and Y was &amp;gt; 40%. Safety data were collected up to 30 days after booster vaccination. Results A total of 471 persons were enrolled. Sufficiency of a MenACYW-TT booster was demonstrated for MPSV4- and for MenACYW-TT-primed subjects. hSBA seroresponse rates were higher among MenACYW-TT- vs MPSV4-primed subjects (79.3%–93.1% vs 49.2%–60.8%, respectively). Three to 7 years after primary vaccination, hSBA geometric mean titers (GMTs) and seroprotection rates (SPRs) declined in both MenACYW-TT- and MPSV4-primed subjects, with hSBA GMTs and SPRs for serogroups C, W, and Y generally remaining higher for MenACYW-TT- vs MPSV4-primed subjects; those for serogroup A were similar regardless of priming vaccine. Rates of adverse events following a MenACYW-TT booster were similar between MenACYW-TT- and MPSV4-primed subjects. No safety concerns were identified. Conclusion A MenACYW-TT booster was well tolerated and immunogenic when administered to either MPSV4- or MenACYW-primed adults aged ≥ 59 years. Up to 7 years after primary vaccination, immune persistence for serogroups C, W, and Y tended to be greater for MenACYW-TT vs MPSV4. Disclosures Corwin A. Robertson, MD, MPH, FACP, Sanofi Pasteur (Employee, Other Financial or Material Support, Stockholder) Alexandre Selmani, PhD, Sanofi Pasteur (Employee) Katherine Galarza, MD, Sanofi Pasteur (Employee) Philipp Oster, MD, Sanofi Pasteur (Employee, Stockholder)

632. Clinical Experience with a New Fully Liquid Presentation of the MenACWY-CRM Vaccine. Results from Two Multicenter, Randomized, Controlled, Observer-Blind, Phase 2b Studies

Abstract Background Currently, licensed MenACWY-CRM conjugate vaccine presentation (Lyo/Liq) consists of two vials (lyophilized MenA, liquid MenCWY) to be reconstituted before injection. A new, fully liquid, single vial formulation has been developed and evaluated in two clinical studies in adolescents and adults aimed at demonstrating immunological non-inferiority of the liquid presentation for MenA. Methods Overall, 1337 subjects, 10 to 40 years of age (y), were exposed to a single 0.5 mL intramuscular dose of MenACWY Liquid and 1332 to MenACWY-CRM(Lyo/Liq). MenACWY-CRM Liquid was aged before administration, to test the vaccine immunogenicity at the end of the intended shelf-life and establish release and end of shelf life specifications. MenACWY-CRM(Lyo/Liq) was used as comparator and was not aged. In study 1 (NCT03652610), the Liquid vaccine underwent an ageing process under controlled conditions to reach ~30% MenA free saccharide (FS). In study 2 (NCT03433482), the Liquid vaccine was naturally aged at 2–8°C for approximately 24 and 30 months. Primary immunogenicity objective in both studies was non-inferiority of MenACWY-CRM liquid to licensed vaccine, as measured by human serum bactericidal assay (hSBA) geometric mean titers (GMTs) against MenA, 1-month post-vaccination. Results In both studies, for each between-group ratio of MenA hSBA GMTs, lower limits of the 95% confidence intervals (CIs) were greater than the prespecified non-inferiority margin (0.5), thus meeting the non-inferiority immunogenicity objective. Irrespectively of the vaccine presentation tested, over 82% of participants achieved MenA hSBA titers ≥ 8 in study 1 and at least 92% in study 2. The immunogenicity of MenACWY-CRM Liquid was similar to that of MenACWY-CRM(Lyo/Liq) when analyzed by serogroup, overall. No related serious adverse events were reported for both presentations. Conclusion After ageing, the new MenACWY-CRM Liquid demonstrated the ability to elicit non-inferior bactericidal responses against MenA compared to licensed formulation. The new full-liquid presentation is expected to increase the user-friendliness of the vaccine as well as to reduce reconstitution errors in the future, with a similar safety profile to that of the licensed vaccine presentation. Disclosures Javier Díez-Domingo, MD, PhD, GSK (Grant/Research Support)Sanofi (Grant/Research Support) Corinne Vandermeulen, MD PhD, GSK (Grant/Research Support)MSD (Grant/Research Support)Pfizer (Grant/Research Support) Tauseefullah Akhund, MD, MSc, MPH, GSK (Employee, Shareholder) Marco Costantini, MSc, MBA, EMPHA, GSK (Employee) Puneet Vir Singh, MBBS, PGDCD, GSK (Employee, Shareholder) Venere Basile, MSc, GSK (Employee, Shareholder) Elena Fragapane, MD, GSK (Employee, Shareholder) Maria Lattanzi, MD, PhD, GSK (Employee, Shareholder) Michele Pellegrini, MD, PhD, Michele Pellegrini (Employee, Shareholder)

Antibacterial activity and action mechanism of a novel chitosan oligosaccharide derivative against dominant spoilage bacteria isolated from shrimp Penaeus vannamei

With the aim of exploring the potential application of a novel chitosan oligosaccharide derivative (COS-All-Tio) in shrimp preservation, six dominant spoilage bacteria in the spoiled shrimp (Penaeus vannamei) were isolated and identified as Shewanella putrefaciens (RMS1), S. putrefaciens (S2), Pseudomonas weihenstephanensis (P1), P. gessardii (P2), Aeromonas bestiarum (A1) and Aeromonas molluscorum (A2). The antibacterial effect of COS-All-Tio against the six bacterial isolates were studied. Bacterial inhibition zone determination, and minimum inhibitory concentration and minimum bactericidal concentration assays indicated that the antibacterial activity of COS-All-Tio was greatly improved when compared to that of chitosan oligosaccharide (COS). The antibacterial mechanism investigation against S. putrefaciens (RMS1) revealed that COS-All-Tio could inhibit bacterial growth by influencing of membrane integrity. Such disturbance of membrane structure resulted in the leakage of intracellular substance of the bacteria. A strong synergistic antibacterial effect against S. putrefaciens (RMS1) was observed when COS-All-Tio was used in combination with food preservatives (e.g. ε-polylysine hydrochloride). Therefore, COS-All-Tio might have potential in shrimp preservation.

Assessment of Serum Bactericidal and Opsonophagocytic Activity of Antibodies to Gonococcal Vaccine Targets.

There is no vaccine available to prevent Neisseria gonorrhoeae infection, however there is currently a high level of interest in developing gonococcal vaccines due to the increasing number of cases and continuing emergence of antimicrobial resistance worldwide. A key aspect of vaccine development is the investigation of the functional immune response raised to the vaccine targets under investigation. Here, we describe two assays used to assess the functional immune response raised against gonococcal vaccine targets: the serum bactericidal assay (SBA) and the opsonophagocytic assay (OPA).

An adsorption method to prepare specific antibody-depleted normal human serum as a source of complement for human serum bactericidal assays for Salmonella

Serum bactericidal assays (SBA) are valuable for assessing the functional activity of natural and vaccine-induced antibodies against many Gram-negative bacteria, such as meningococcus and Salmonella. However, SBA often require an exogenous source of complement and the presence of pre-existing naturally acquired antibodies limits the use of human complement for this purpose. To remove pre-existing Salmonella-specific antibodies, in the context of SBA for Salmonella vaccine research, we incubated human sera with preparations of Salmonella. By incubating at 4 °C, pre-existing antibodies were adsorbed onto the Salmonella bacteria with only minimal complement deposition. We assessed the effects of adsorption on specific antibody levels, complement activity and the bactericidal activity of sera using flow cytometry, SBA and haemolytic assays. Adsorption removed Salmonella-specific antibodies and bactericidal activity against Salmonella from whole serum but was not detrimental to serum complement activity, even after five adsorption cycles. Bactericidal activity could be reconstituted in the adsorbed serum by the addition of exogenous specific antibodies. Sera preadsorbed with Salmonella are suitable as a source of human complement to measure the bactericidal activity of Salmonella antibodies. The adsorption method can be used to deplete, simply and rapidly, specific antibodies from serum to prepare a source of human complement for use in SBA for vaccine research and assessment.