AUTHOR=Zhao Xinxin , Dai Qinlong , Jia Renyong , Zhu Dekang , Liu Mafeng , Wang Mingshu , Chen Shun , Sun Kunfeng , Yang Qiao , Wu Ying , Cheng Anchun 

TITLE=Two Novel Salmonella Bivalent Vaccines Confer Dual Protection against Two Salmonella Serovars in Mice

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=7

YEAR=2017

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2017.00391

DOI=10.3389/fcimb.2017.00391

ISSN=2235-2988

ABSTRACT=<p>Non-typhoidal <italic>Salmonella</italic> includes thousands of serovars that are leading causes of foodborne diarrheal illness worldwide. In this study, we constructed three bivalent vaccines for preventing both <italic>Salmonella</italic> Typhimurium and <italic>Salmonella</italic> Newport infections by using the aspartate semialdehyde dehydrogenase (Asd)-based balanced-lethal vector-host system. The constructed Asd<sup>+</sup> plasmid pCZ11 carrying a subset of the <italic>Salmonella</italic> Newport O-antigen gene cluster including the <italic>wzx-wbaR-wbaL-wbaQ-wzy-wbaW-wbaZ</italic> genes was introduced into three <italic>Salmonella</italic> Typhimurium mutants: SLT19 (Δ<italic>asd</italic>) with a smooth LPS phenotype, SLT20 (Δ<italic>asd</italic> Δ<italic>rfbN</italic>) with a rough LPS phenotype, and SLT22 (Δ<italic>asd</italic> Δ<italic>rfbN</italic> Δ<italic>pagL::T araC</italic> P<sub>BAD</sub><italic>rfbN</italic>) with a smooth LPS phenotype when grown with arabinose. Immunoblotting demonstrated that SLT19 harboring pCZ11 [termed SLT19 (pCZ11)] co-expressed the homologous and heterologous O-antigens; SLT20 (pCZ11) exclusively expressed the heterologous O-antigen; and when arabinose was available, SLT22 (pCZ11) expressed both types of O-antigens, while in the absence of arabinose, SLT22 (pCZ11) expressed only the heterologous O-antigen. Exclusive expression of the heterologous O-antigen in <italic>Salmonella</italic> Typhimurium decreased the swimming ability of the bacterium and its susceptibility to polymyxin B. Next, the <italic>crp</italic> gene was deleted from the three recombinant strains for attenuation purposes, generating the three bivalent vaccine strains SLT25 (pCZ11), SLT26 (pCZ11), and SLT27 (pCZ11), respectively. Groups of BALB/c mice (12 mice/group) were orally immunized with 10<sup>9</sup> CFU of each vaccine strain twice at an interval of 4 weeks. Compared with a mock immunization, immunization with all three vaccine strains induced significant serum IgG responses against both <italic>Salmonella</italic> Typhimurium and <italic>Salmonella</italic> Newport LPS. The bacterial loads in the mouse tissues were significantly lower in the three vaccine-strain-immunized groups than in the mock group after either <italic>Salmonella</italic> Typhimurium or <italic>Salmonella</italic> Newport lethal challenge. All of the mice in the three vaccine-immunized groups survived the lethal <italic>Salmonella</italic> Typhimurium challenge. In contrast, SLT26 (pCZ11) and SLT27 (pCZ11) conferred full protection against lethal <italic>Salmonella</italic> Newport challenge, but SLT25 (pCZ11) provided only 50% heterologous protection. Thus, we developed two novel <italic>Salmonella</italic> bivalent vaccines, SLT26 (pCZ11) and SLT27 (pCZ11), suggesting that the delivery of a heterologous O-antigen in attenuated <italic>Salmonella</italic> strains is a prospective approach for developing <italic>Salmonella</italic> vaccines with broad serovar coverage.</p>