Genotypic and In vivo assessment of Environmental Escherichia coli Isolates as a potential vaccine against Shigellosis

In a previous study, a number of environmental E. coli isolates showed cross-reactivity with number of group- and type-specific Shigella antisera due to sharing common surface proteins and LPS. Our collection of serologically cross-reactive isolates have covered a number of serotypes which are prevalence in ourbreaks and thus can be included in vaccine development regime. These isolates has already been assessed for its potential as vaccine combating shigellosis (unpublished data). The sero cross reactivity was screened by slide aglutination method and confirmed by Western blot analysis. Multiplex PCR assays were conducted for detection of five adhesin genes and nine E. coli - Shigella spp. specific virulent genes. None of the isolates were PCR positive for virulent genes, hence characterized as avirulent E. coli. The lack of virulent properties of the environmental isolates and serological similarities could make them a potential candidate for development as a live vaccine against shigellosis. In this research, we planned to assess the safety by molecular analyses i.e., sequencing the virulence associated genes and gene cassettes, pathogenicity islands and related domains of the chromosome by next generation sequencing techniques. Isolates which would found non pathogenic will be assessed for in vivo analyses. Sereny test, rabbit ileal loop test and intra peritoneal infection of chicks will be performed for the safety assessment and selection of appropriate animal model for further analysis. After selection and optimization of the animal models, immunization will be performed with virulent Shigella spp. and E. coli vaccine candidates to assess the cross protection and serological reactions. Vaccine research to combat Shigellosis has initiated long before but a satisfactory vaccine is still not in market. Models used by previous studies are mice, chicken, rabbit, guinea pigs and monkeys. We have also planned to assess these models and select a suitable model for immunization and challenge considering suitability, availability and costs. The methodology using animal models will be sent for ethical approval and performed according to ethical regulations.