Abstract
Human typhoid fever caused by Salmonella Typhi still poses a severe global disease burden in developing countries despite the availability of commercial vaccines. In this study, we constructed a non-living S. Typhi Ty21a vaccine candidate by employing a lambda (λ) phage-derived holin-endolysin system to efficiently construct bacterial ghosts. The lysis plasmid pJHL464 harbors an R lysis cassette that is stringently regulated by dual promoters containing cI857/λPR and ParaBAD/araC components. The plasmid was introduced into an asd gene-deleted S. Typhi Ty21a strain designated JOL1675. The in vitro expression of endolysin (~17.76 kDa) in the subsequent JOL1675 vaccine construct when grown under lysis inducible conditions was validated by immunoblotting. In scanning electron microscopy analysis, surface transmembrane tunnels and a collapsed body were visualized in the ghosts. Following 48 h of lysis, no viable JOL1675 cells remained, indicating that lysis of all cells was achieved. Subcutaneous immunizations of mice with the JOL1675 ghosts produced significantly increasing titers of serum IgG and vaginal wash secretory IgA antibodies against JOL1675 outer membrane proteins during the observational period. Further, serum collected at 6 weeks post-immunization of rabbits exhibited effective bactericidal activity against wild type S. Typhi in the presence of complement. These data showed that JOL1675 ghosts are highly immunogenic and elicit humoral and mucosal responses expected to correlate with protective immunity against S. typhi. Collectively, our findings support the conclusion that incorporating a λ phage holin-endolysin-mediated lysis construct into S. Typhi is an efficient strategy for developing a novel and safe non-living typhoid vaccine candidate.
Highlights
IntroductionTwo approved typhoid vaccines, a parenteral Vi capsular polysaccharide vaccine (Typherix® or Typhim Vi®) and an oral live attenuated Ty21a (Vivotif®), are available [3]
An immunoreactive band of ~17.7 kDa corresponding to the predicted molecular mass of the endolysin protein was detected in the pellet of JOL1675 ghosts incubated under optimal lysis conditions at 42°C in the absence of arabinose for 48 h (Figure 2)
Given the capacity of holin-endolysin to hydrolyze PG and induce programmed cell death, the R lysis cassette containing R, S, Rz, and Rz1 was incorporated into a novel plasmid pJHL464 for use in producing bacterial ghosts
Summary
Two approved typhoid vaccines, a parenteral Vi capsular polysaccharide vaccine (Typherix® or Typhim Vi®) and an oral live attenuated Ty21a (Vivotif®), are available [3]. Despite the presence of these licensed vaccines and a high demand for vaccines in endemic areas, the vaccines are mostly offered to persons traveling from developed countries to affected countries rather than to the individuals residing in the endemic countries due to poor utilization of health care services [4, 5], resulting in disease eradication failure. Live attenuated Ty21a vaccines still carry the potential risk of unacceptable reactogenicity [7]. A new strategy to develop more optimal typhoid vaccine candidate has great potential value
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
