Characterization of Citrobacter sp. line 328 as a source of Vi for a Vi-CRM197 glycoconjugate vaccine against Salmonella Typhi

Simona Rondini,Luisa Lanzilao,Francesca Micoli,Allan J Saul,Vito Di Cioccio,Ivan Pisoni,Laura B Martin

doi:10.3855/jidc.2495

Abstract

Salmonella enterica serovar Typhi is the causative agent of typhoid fever with over 22 million cases and over 200,000 deaths reported annually. A vaccine is much needed for use in young children and the Novartis Vaccines Institute for Global Health (NVGH) is developing a conjugate vaccine which targets S. Typhi Vi capsular polysaccharide. Here we describe a method suitable for industrial scale production of the Vi antigen based on expression by a Citrobacter line. We optimized the production of Vi by selecting a suitable Citrobacter strain (Citrobacter 328) that yields high and stable expression of Vi in chemically defined medium under industrial-scale fermentation conditions. Vi-CRM197 made using Vi from Citrobacter 328 elicited high anti-Vi antibody levels in mice and rabbits. Citrobacter 328 is a suitable strain for production of Vi for conjugate anti-Typhi vaccines. Being a BSL-1 organism, which grows in defined medium and stably produces high yields of Vi, it offers excellent potential for safe production of inexpensive vaccines for populations at risk of typhoid fever.

Highlights

Salmonella enterica serovar Typhi is the causative agent of typhoid fever with over 22 million cases and over 200,000 deaths reported annually
We have identified a wild type Citrobacter line 328 that showed both homogeneity and stability of Vi expression, and whose Vi was released into the culture supernatant when grown in chemically defined medium
We evaluated antibody responses of Vi-CRM197 conjugate (in text defined as Vi(328)-CRM197) elicited in sera of mice and rabbits, compared with a previously synthesized CRM197conjugate with Vi derived from WR7011 (in text defined as Vi(WR7011)-CRM197)

Summary

Introduction

Salmonella enterica serovar Typhi is the causative agent of typhoid fever with over 22 million cases and over 200,000 deaths reported annually. Methodology: Here we describe a method suitable for industrial scale production of the Vi antigen based on expression by a Citrobacter line. We optimized the production of Vi by selecting a suitable Citrobacter strain (Citrobacter 328) that yields high and stable expression of Vi in chemically defined medium under industrial-scale fermentation conditions. Conclusions: Citrobacter 328 is a suitable strain for production of Vi for conjugate anti-Typhi vaccines. Being a BSL-1 organism, which grows in defined medium and stably produces high yields of Vi, it offers excellent potential for the safe production of inexpensive vaccines for populations at risk of typhoid fever. Vi consists of repeating ([alpha]14),2-deoxy-2-N-acetyl galacturonic acid moieties, variably O-acetylated at C3 position, and is a target of protective immunity against typhoid fever [5]

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Conclusion