Chaperones Promote Remarkable Solubilization of Salmonella enterica serovar Enteritidis Flagellin Expressed in Escherichia coli

BACKGROUND

Flagellin of Salmonella enterica serovar Enteritidis (SEF) stimulates immune responses to both itself and coapplied antigens. It is therefore used in vaccine development and immunotherapy. Removal of pathogenic S. enterica ser. Enteritidis from SEF production process is advantageous due to the process safety improvement. The protein solubility analysis using SDS-PAGE indicated that 53.49% of SEF expressed in Escherichia coli formed inclusion bodies. However, the protein recovery from inclusion bodies requires a complex process with a low yield.

OBJECTIVE

We thus aim to study possibility of enhancing SEF expression in E. coli in soluble form using chemical and molecular chaperones.

METHODS

Chemical chaperones including arginine, sorbitol, trehalose, sodium chloride and benzyl alcohol were used as cultivation medium additives during SEF expression. SEF solubilization by coexpression of molecular chaperones DnaK, DnaJ, and GrpE was also investigated.

RESULTS

All of the chemical chaperones were effective in improving SEF solubility. However, sorbitol showed the most profound effect. SEF solubilization by molecular chaperones was slightly better than that using sorbitol and this approach enhanced noticeably SEF soluble concentration and SEF solubility percentage to almost two folds and 96.37% respectively. Results of limited proteolysis assay and native PAGE indicated similar conformational states and proper folding for SEF obtained without using chaperones and for those obtained using sorbitol and the molecular chaperones. However, the molecular chaperones based system was less costly than the sorbitol based system.

CONCLUSION

The coexpression of molecular chaperones was then considered as the most appropriate approach for soluble SEF production. Therefore, SEF production for medical purposes is expected to be facilitated.

A severe gastroenteritis outbreak of Salmonella enterica serovar Enteritidis PT8, with PFGE profile XbaI.0024 and MLVA profile 2-9-7-3-2 following a christening reception, Greece, 2016

In June 2016, a Salmonella enterica serovar Enteritidis outbreak (n = 56) occurred after a christening reception in Central Greece, mainly affecting previously healthy adults; one related death caused media attention. Patients suffered from profuse diarrhoea, fever and frequent vomiting episodes requiring prolonged hospitalisation and sick leave from work, with a 54% hospital admission rate. The majority of cases experienced serious illness within <12 h of attending the party. We investigated the outbreak to identify the source(s) of infection and contributing factors to the disease severity. From the retrospective cohort study, the cheesy penne pasta was the most likely vehicle of infection (relative risk 7·8; 95% confidence interval 3·6-16·8), explaining 79% of the cases. S. enterica ser. Enteritidis isolates were typed as phage-type PT8, pulsed-field gel electrophoresis type XbaI.0024, multiple locus variable-number tandem repeat analysis-type 2-9-7-3-2. The strain did not share the single-nucleotide polymorphism address of the concurrent European S. enterica ser. Enteritidis PT8 outbreak clusters. Following five consecutive years with no documented S. enterica ser. Enteritidis outbreaks in Greece, this outbreak, likely associated with a virulent strain, prompted actions towards the enhancement of the national Salmonella molecular surveillance and control programmes including the intensification of training of food handlers for preventing similar outbreaks in the future. Advanced molecular techniques were useful in distinguishing unrelated outbreak strains.