Immunological evaluation of vi-vapsular polysaccharide of Salmonella typhi vaccine by serum bactericidal assay

Abstract number: P1328

Ahmadi H., Tabaraiee B., Siadat S.D., Poor mirza gholi F., Norouzian D., Nejati M., Hedayati M.H., Mahmoodi K., Sharifat Salmani A., Abbasi M., Karbasian M., Adli Moghadam A.

Objectives:Salmonella typhi Vi-capsular polysaccharide (Vi-CPS) is an essential virulence factor and a safe and reliable vaccine against typhoid fever (Acharya et al, 1975: Szu et al, 1994: Yang et al, 2001). Since there is no any animal model for Salmonella typhi fever to evaluate protective efficacy of Vi-CPS vaccine, we recommend, serum bactericidal assay (SBA) as a golden standard to evaluate its potency.

Methods: Vi-CPS was extracted from Salmonella typhi Ty6S (CSBPI-B-191) according to the modified Gotschlich method (Ahmadi et al, 1999). Fifty mg of purified Vi-CPS was injected intramuscularly into three groups of five rabbits, Groups 2 and 3 were received additional booster dose of 50 mg Vi-CPS on day 15 and days 15 and 30 respectively.

Each group of pooled serum was tested by SBA on days 0, 15, 30 and 45.

Results: The titers of SBA of anti Vi-CPS were 4, 16 and 16 for group 1 and 4, 32 and 32 for group 2 and 16, 64 and 64 for group 3 in days 15, 30 and 45 respectively.

Our investigation reveals that; Vi-CPS is a potent immunogen. Because, at even one does of 50 mg, could show an excellent bactericidal effect against pathogenic Salmonella typhi.

Conclusions: Though Vi-CPS is a reliable vaccine against typhoid fever but sometimes depolymerisation take place during purification and may cause low potency. This draw back can be resolved through potency test. Since passive hemaglutination test recommended by WHO., does not indicate potency of the vaccine, we recommend SBA method to evaluate the ability of Vi-CPS to kill pathogenic Salmonella typhi, as it has been shown in our present results.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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