A GMMA-CPS-Based Vaccine for Non-Typhoidal Salmonella

Outer membrane vesicles as a platform for the discovery of antibodies to bacterial pathogens

Bacterial outer membrane vesicles (OMVs) are nanosized spheroidal particles shed by gram-negative bacteria that contain biomolecules derived from the periplasmic space, the bacterial outer membrane, and possibly other compartments. OMVs can be purified from bacterial culture supernatants, and by genetically manipulating the bacterial cells that produce them, they can be engineered to harbor cargoes and/or display molecules of interest on their surfaces including antigens that are immunogenic in mammals. Since OMV bilayer-embedded components presumably maintain their native structures, OMVs may represent highly useful tools for generating antibodies to bacterial outer membrane targets. OMVs have historically been utilized as vaccines or vaccine constituents. Antibodies that target bacterial surfaces are increasingly being explored as antimicrobial agents either in unmodified form or as targeting moieties for bactericidal compounds. Here, we review the properties of OMVs, their use as immunogens, and their ability to elicit antibody responses against bacterial antigens. We highlight antigens from bacterial pathogens that have been successfully targeted using antibodies derived from OMV-based immunization and describe opportunities and limitations for OMVs as a platform for antimicrobial antibody development. KEY POINTS: • Outer membrane vesicles (OMVs) of gram-negative bacteria bear cell-surface molecules • OMV immunization allows rapid antibody (Ab) isolation to bacterial membrane targets • Review and analysis of OMV-based immunogens for antimicrobial Ab development.

Prevalence and distribution of non-typhoidal Salmonella enterica serogroups and serovars isolated from normally sterile sites: A global systematic review

To inform coverage by potential vaccines, we aimed to systematically review evidence on the prevalence and distribution of non-typhoidal Salmonella enterica serogroups and serovars. We searched four databases from inception through 4 June 2021. Articles were included that reported at least one non-typhoidal S. enterica strain by serogroup or serovar isolated from a normally sterile site. Of serogrouped isolates, we pooled the prevalence of serogroup O:4, serogroup O:9, and other serogroups using random-effects meta-analyses. Of serotyped isolates, we pooled the prevalence of Salmonella Typhimurium (member of serogroup O:4), Salmonella Enteritidis (member of serogroup O:9), and other serovars. Of 82 studies yielding 24,253 serogrouped isolates, the pooled prevalence (95% CI) was 44.6% (36.2%-48.2%) for serogroup O:4, 45.5% (37.0%-49.1%) for serogroup O:9, and 9.9% (6.1%-13.3%) for other serogroups. Of serotyped isolates, the pooled prevalence (95%CI) was 36.8% (29.9%-44.0%) for Salmonella Typhimurium, 37.8% (33.2%-42.4%) for Salmonella Enteritidis, and 18.4% (11.4%-22.9%) for other serovars. Of global serogrouped non-typhoidal Salmonella isolates from normally sterile sites, serogroup O:4 and O:9 together accounted for 90%, and among serotyped isolates, serovars Typhimurium and Enteritidis together accounted for 75%. Vaccine development strategies covering serogroups O:4 and O:9, or serovars Typhimurium and Enteritidis, have the potential to prevent the majority of non-typhoidal Salmonella invasive disease.

Is it time to move on to gene-based Salmonella typing: Evidence and implications

Non-typhoidal Salmonella (NTS) is the major cause of foodborne infections globally, with considerable morbidity and mortality. The accurate identification of Salmonella serovars is important in disease management and public health surveillance. However, traditional serotyping methods are laborious, time-consuming and may produce ambiguous results. In this study, we evaluated traditional serotyping and seven gene-based multilocus sequence typing (MLST) methods to determine the serogroups of Salmonella strains. This study analysis suggests that MLST based serotyping is accurate in serogroup identification and discrimination of Salmonella serovars compared to the traditional serotyping method and can be implemented in routine clinical practice.

Synthetic Glycans to Improve Current Glycoconjugate Vaccines and Fight Antimicrobial Resistance

Antimicrobial resistance (AMR) is emerging as the next potential pandemic. Different microorganisms, including the bacteria Acinetobacter baumannii, Clostridioides difficile, Escherichia coli, Enterococcus faecium, Klebsiella pneumoniae, Neisseria gonorrhoeae, Pseudomonas aeruginosa, non-typhoidal Salmonella, and Staphylococcus aureus, and the fungus Candida auris, have been identified by the WHO and CDC as urgent or serious AMR threats. Others, such as group A and B Streptococci, are classified as concerning threats. Glycoconjugate vaccines have been demonstrated to be an efficacious and cost-effective measure to combat infections against Haemophilus influenzae, Neisseria meningitis, Streptococcus pneumoniae, and, more recently, Salmonella typhi. Recent times have seen enormous progress in methodologies for the assembly of complex glycans and glycoconjugates, with developments in synthetic, chemoenzymatic, and glycoengineering methodologies. This review analyzes the advancement of glycoconjugate vaccines based on synthetic carbohydrates to improve existing vaccines and identify novel candidates to combat AMR. Through this literature survey we built an overview of structure-immunogenicity relationships from available data and identify gaps and areas for further research to better exploit the peculiar role of carbohydrates as vaccine targets and create the next generation of synthetic carbohydrate-based vaccines.

Polysaccharide Vaccines: A Perspective on Non-Typhoidal Salmonella

Polysaccharides are often the most abundant antigens found on the extracellular surfaces of bacterial cells. These polysaccharides play key roles in interactions with the outside world, and for many bacterial pathogens, they represent what is presented to the human immune system. As a result, many vaccines have been or currently are being developed against carbohydrate antigens. In this review, we explore the diversity of capsular polysaccharides (CPS) in Salmonella and other selected bacterial species and explain the classification and function of CPS as vaccine antigens. Despite many vaccines being developed using carbohydrate antigens, the low immunogenicity and the diversity of infecting strains and serovars present an antigen formulation challenge to manufacturers. Vaccines tend to focus on common serovars or have changing formulations over time, reflecting the trends in human infection, which can be costly and time-consuming. We summarize the approaches to generate carbohydrate-based vaccines for Salmonella, describe vaccines that are in development and emphasize the need for an effective vaccine against non-typhoidal Salmonella strains.