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Title of Thesis

Preparation of Multiple Conjugates (LPS- Protein) for Immunization Against Typhoidal Diseases


Aamir Ali

Institute/University/Department Details
National Institute for Biotechnology and Genetic Engineering (NIBGE), Faisalabad & Quaid-i-Azam University, Islamabad
Biotechnology and Genetic Engineering
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
Preparation, Multiple, Conjugates, LPS- Protein, Immunization, Typhoidal, Diseases, pathogens, lipopolysaccharide

Classically Salmonella enterica serovar Typhi (S. Typhi) is associated with typhoid, a major health problem in developing countries. However, in recent years Salmonella enterica serovar Paratyphi A (S. Paratyphi A) and Vi negative variants of S. Typhi have emerged rapidly. For development of multiple protein-polysaccharide conjugates with potential to be used as vaccines, we needed to have a first hand knowledge of local distribution of these pathogens. For this purpose, we developed a nested multiplex PCR targeting 5 different genes for differential diagnosis of typhoidal pathogens which has been optimized to be directly applicable on clinical blood samples. Out of 42 multiplex PCR positive blood samples, 26, 9, and 2 were Vi-positive S. Typhi, Vi-negative S. Typhi and S. Paratyphi A, respectively and 5 patients were found to have mixed infection. Seventeen patients grew Salmonella from blood culture and the remaining 25 were positive in the Salmonella specific PCR. Tests with several common pathogens confirmed the specificity of the assay. We conclude that the proposed multiplex PCR is rapid, sensitive and specific for the diagnosis of typhoidal pathogens directly from blood samples. Detection of Vi negative strains of S. Typhi and S. Paratyphi A among typhoidal patients suggested the need to work on vaccines which are not based on Vi polysaccharide only. Therefore, O-specific polysaccharides (OSP) purified from lipopolysaccharides (LPS) of S. Typhi and S. Paratyphi A were conjugated with diphtheria toxoid (DT) using adipic acid dihydrazide (ADH) as linker, and evaluated for immunogenicity in mice. Use of DT as carrier protein for Salmonellae has not been reported before. S. Typhi OSP-AH-DT conjugate 1 and 2 elicited significantly higher IgG anti-LPS ELISA titer (P = 0.0241 and 0.0245 respectively) than polysaccharide alone. The injection schedule-B (three injections with 4-weeks interval) was found better than schedule-A (three injections with 2-weeks interval). The conjugate of S. Paratyphi A OSP with DT without linker molecule did not elicit sufficient immune response to be used as conjugate vaccine candidate while antibody response against S. Paratyphi A OSP-AH-DT onjugate was found significantly higher (P = 0.0446) than polysaccharide alone.

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S. No. Chapter Title of the Chapters Page Size (KB)


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1.1 The genus Salmonella
1.2 Epidemiology
1.3 Pathogenesis
1.4 Clinical features
1.5 Drug resistance
1.6 Diagnosis
1.7 First research objective
1.8 Vaccines against typhoidal Salmonella
1.9 Bacterial polysaccharide-protein conjugate vaccines
1.10 Second research objective

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2.1 Bacterial isolates
2.2 Purification of the strains
2.3 Biochemical identification of the bacterial strains
2.4 Studies on patients
2.5 Molecular analysis
2.6 Polymerase chain reaction (PCR)
2.7 Agarose gel electrophoresis

2.8 Bacterial strains
2.9 Fermentation
2.10 Phenol extraction of lipopolysaccharides (LPS) from S. Typhi and S. Paratyphi A
2.11 Acid hydorlysis of S. Typhi LPS to purify O-specific polysaccharides (OSP)
2.12 Acid hydorlysis of S. Paratyphi A LPS to purify O-specific polysaccharides (OSP)
2.13 Derivatization of S. Typhi OSP with adipic acid dihydrazide (ADH)
2.14 Derivatization of S. Paratyphi A OSP with adipic acid dihydrazide (ADH)
2.15 Diphtheria toxoid (DT) as a carrier protein for conjugation with Salmonella polysaccharides
2.16 Conjugation of S. Typhi OSP-AH with diphtheria toxoid
2.17 Conjugation of S. Paratyphi OSP with diphtheria toxoid
2.18 Conjugation of derivatized S. Paratyphi A OSP (S. Paratyphi A OSP-AH) with diphtheria toxoid (DT)
2.19 High performance liquid chromatography (HPLC) analyses
2.20 Development of standard hyper immune sera against whole cell of S. Typhi and S. Paratyphi A in mice
2.21 Immunogenicity evaluation of the prepared conjugates through mice immunization
2.22 Immuno assay for determination of mice serum IgG antibody levels by enzyme linked immumo orbant assay (ELISA)

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3.1 Salmonella strains
3.2 Studies on patients
3.3 Polymerase chain reaction (PCR)
3.4 Preparation of O-specific polysaccharides (OSP) from Salmonella
3.5 Derivatization of Salmonella OSP with ADH
3.6 Conjugation of S. Typhi OSP-AH with DT
3.7 Conjugation of S. Paratyphi A OSP with DT
3.8 High performance liquid chromatography (HPLC) analyses
3.9 Development of high titer mice antisera (hyper immune sera) against S. Typhi and S. Paratyphi A LPS
3.10 Immunogenicity evaluation of the conjugates in mice

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4.1 Diagnosis
4.2 Vaccines

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