Development and Properties of Francisella tularensis Subsp. holarctica 15 NIIEG Vaccine Strain without the recD Gene.

Vitaly Pavlov,Galina Titareva,Tatiana Gapelchenkova,Galina Vakhrameeva,Mikhail E Platonov,Tatiana Kombarova,Raisa Mironova,Alexander Mokrievich,Ivan Dyatlov

doi:10.3390/vaccines10010108

Vitaly Pavlov, Galina Titareva + Show 7 more

Open Access

https://doi.org/10.3390/vaccines10010108

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Abstract

The genomic analysis of all subspecies F. tularensis, as found in Gen Bank NCBI, reveals the presence of genes encoding proteins like to the multifunctional RecBCD enzyme complex in E. coli and other bacteria. To date, the role of the recD gene in F. tularensis, which encodes the alpha chain of exonuclease V, in DNA metabolism processes, has not been studied either in vitro or in vivo. F. tularensis subsp. holarctica 15 NIIEG, a vaccine strain, served as the basis to create the F. tularensis 15D strain with recD deletion. The lack of the recD gene suppresses the integration of suicide plasmids with F. tularensis genome fragments into the chromosome. The modified strain showed reduced growth in vitro and in vivo. This study shows that such deletion significantly reduces the virulence of the strain in BALB/c mice.

Highlights

Tularemia is an acute infectious disease in humans and animals that is etiologically caused by the bacteria Francisella tularensis; humans’ high susceptibility to the pathogen makes this disease extremely dangerous for subspecies of F. tularensis subsp. tularensis [1,2]
At the N-terminus of the RecD protein in F. tularensis subsp. holarctica and F. philomiragia, there is a 9 amino acid deletion, which distinguishes these species from others
One of the possible directions for stabilizing and reactogenicity reducing of existing tularemia vaccines is the modification or deletion of genes, the products of which are involved in repair processes and intragenomic rearrangements

Summary

Introduction

Tularemia is an acute infectious disease in humans and animals that is etiologically caused by the bacteria Francisella tularensis; humans’ high susceptibility to the pathogen makes this disease extremely dangerous for subspecies of F. tularensis subsp. tularensis (mortality rate of up to 60% in untreated cases) [1,2]. Endemic areas of Russia use a live vaccine based on the F. tularensis subsp. F. tularensis LVS (live vaccine strain) in case of an emergency, which is obtained by a series of passages of F. tularensis 15 in vitro [4]. The LVS strain has the same shortcomings: besides reactogenicity, the culture exhibits some dissociation during culturing [6,7] All of this prevents the FDA from licensing a live tularemia vaccine in the USA [8]. In the LVS and 15 NIIEG strains, the recD gene forms a single operon with the recB (FTL_0669). The genomes of all F. tularensis subspecies have a recD-like nucleotide sequences: FTL_0670. We describe the construction of F. tularensis 15 NIIEG strain without recD gene and further research of its properties. Complementation of the deletion restores the molecular and biological properties of the modified strain

Materials and Methods

Results and Discussion

Tularensis Strain

Discussion