Glycoconjugate vaccines against Salmonella enterica serovars and Shigella species: existing and emerging methods for their analysis

Abstract

The global spread of enteric disease, the increasingly limited options for antimicrobial treatment and the need for effective eradication programs have resulted in an increased demand for glycoconjugate enteric vaccines, made with carbohydrate-based membrane components of the pathogen, and their precise characterisation. A set of physico-chemical and immunological tests are employed for complete vaccine characterisation and to ensure their consistency, potency, safety and stability, following the relevant World Health Organization and Pharmacopoeia guidelines. Variable requirements for analytical methods are linked to conjugate structure, carrier protein nature and size and O-acetyl content of polysaccharide. We investigated a key stability-indicating method which measures the percent free saccharide of Salmonella enterica subspecies enterica serovar Typhi capsular polysaccharide, by detergent precipitation, depolymerisation and HPAEC-PAD quantitation. Together with modern computational approaches, a more precise design of glycoconjugates is possible, allowing for improvements in solubility, structural conformation and stability, and immunogenicity of antigens, which may be applicable to a broad spectrum of vaccines. More validation experiments are required to establish the most effective and suitable methods for glycoconjugate analysis to bring uniformity to the existing protocols, although the need for product-specific approaches will apply, especially for the more complex vaccines. An overview of current and emerging analytical approaches for the characterisation of vaccines against Salmonella Typhi and Shigella species is described in this paper. This study should aid the development and licensing of new glycoconjugate vaccines aimed at the prevention of enteric diseases.

Development of high-resolution melting (HRM) assay to differentiate the species of Shigella isolates from stool and food samples

“…Four species of Shigella including S. dysenteriae , S. flexneri , S. Boydii, and S. sonnei are among the main public health threats and food safety concerns around the world in developing and developed countries 3 , 5 . Nowadays, rapid and conventional methods such as hybridisation probes, multiplex PCR with species-specific primers, biochemical identification and serologic tests, which are so expensive or time consuming, have been developed and used to identify and differentiate four species of Shigella in food and clinical isolates 10 , 14 , 16 . Elahi et al recently reported the development of a fluorescence DNA probe nano-biosensor method based on iron and gold nanoparticle to identify different species of Shigella 31 .…”

“…However, they are also expensive and complicated in their implementation. We conclude that a simple, rapid, inexpensive, accurate, specific, and sensitive method must be designed and developed for differentiation of Shigella species isolated from stool and food samples 10 , 15 , 16 .…”

Biophysical Reviews— 2021, the year that was

“…The "Meet the Editors" piece was contributed by Prof. Addmore Shohnai, a Zimbabwean scientist now working in South Africa as a professor (and head) of the Department of Biochemistry at the University of Venda (Shonhai 2021). Of the scientific content articles appearing in this Issue, I would like highlight the following four which involved a scientific letter concerning the use of optical tweezers in a diagnostic assay of sickle cell anemia based on red blood cell plasticity, contributed by a collaborative team of laser physicists and clinicians based in Iran (Mohi et al 2021); a review article submitted by a team from Germany that explored biophysical methods for characterizing the directed movement of immune cells essential to carrying out their role in "immune surveillance" (Vesperini et al 2021); a review article by a group from the UK exploring the biophysical and analytical procedures for characterizing the eliciting glycoconjugate antigens used in the development of novel classes of vaccines for enteric bacteria (such as salmonella) (Bazhenova et al 2021); and finally, a review article by a New Zealand government scientist who discussed molecular biology procedures for engineering protein ligation relays -biochemical pathways in which one protein is attached with extreme specificity to another through a cascade of intermediate shuttle protein reactions (Mabbitt 2021).…”

Evidence of Extended Thermo-Stability of Typhoid Polysaccharide Conjugate Vaccines

“…The subsequent program of the World Health Organization (WHO) to strengthen the development of typhoid conjugate vaccines (TCVs) for vaccination programs led to manufacturing initiatives, human challenge trials, and field studies that have resulted in the rollout of vaccines in Africa and Southeast Asia [6][7][8][9]. Numerous vaccines have been licensed, including Typbar TCV (Bharat Biotech International Limited (BBIL), Hyderabad, India) in 2013, PedaTyph (BioMed, Ghaziabad, India) in 2008, and a TCV produced by Zydus Cadila (Ahmedabad, India) and licensed in 2017 [8], all of which consist of Vi PS, either from S. Typhi conjugated to tetanus toxoid (TT), conjugates with diphtheria toxoid [10], CRM 197 (cross-reacting material 197, a non-toxic variant of diphtheria toxin [11]), and recombinant exotoxin A of Pseudomonas aeruginosa (rEPA) amongst others [12].…”

“…Key stability indicators for TCV that are required for ECTC study include the vaccine's identity, molecular size and integrity of the conjugate (free Vi PS), O-acetylation content of Vi PS, and pH [12]. In this report, the manufacturer conducted a formal ECTC study and also collaborated with a control laboratory for independent evaluation of the vaccine's thermostability.…”