AUTHOR=Zhao Guixin , Duan Wenlong , Zhang Lu , Sun Wenchao , Liu Wan , Zhang Xiaoyu , Zhang Yanying , Shi Qiumei , Wu Tonglei 

TITLE=The peptidoglycan-associated lipoprotein gene mutant elicits robust immunological defense in mice against Salmonella enteritidis

JOURNAL=Frontiers in Microbiology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1422202

DOI=10.3389/fmicb.2024.1422202

ISSN=1664-302X

ABSTRACT=<sec id="sec1"><title>Background</title><p><italic>Salmonella enteritidis</italic> (<italic>S. enteritidis</italic>), a zoonotic pathogen with a broad host range, presents a substantial threat to global public health safety. Vaccination stands as an effective strategy for the prevention and control of <italic>S. enteritidis</italic> infection, highlighting an immediate clinical need for the creation of safe and efficient attenuated live vaccines.</p></sec><sec id="sec2"><title>Methods</title><p>In this study, a <italic>S. enteritidis</italic> peptidoglycan-associated lipoprotein (<italic>pal</italic>) gene deletion strain (Δ<italic>pal</italic>), was constructed. To assess its virulence, we conducted experiments on biofilm formation capability, motility, as well as cell and mouse infection. Subsequently, we evaluated the immune-protective effect of Δ<italic>pal</italic>.</p></sec><sec id="sec3"><title>Results</title><p>It was discovered that deletion of the <italic>pal</italic> gene reduced the biofilm formation capability and motility of <italic>S. enteritidis</italic>. Cell infection experiments revealed that the Δ<italic>pal</italic> strain exhibited significantly decreased abilities in invasion, adhesion, and intracellular survival, with downregulation of virulence gene expression, including <italic>mgtC</italic>, <italic>invH</italic>, <italic>spvB</italic>, <italic>sipA</italic>, <italic>sipB</italic>, <italic>ssaV</italic>, <italic>csgA</italic>, and <italic>pipB</italic>. Mouse infection experiments showed that the LD<sub>50</sub> of Δ<italic>pal</italic> increased by 10<sup>4</sup> times, and its colonization ability in mouse tissue organs was significantly reduced. The results indicated that the <italic>pal</italic> gene severely affected the virulence of <italic>S. enteritidis</italic>. Further, immunogenicity evaluation of Δ<italic>pal</italic> showed a significant enhancement in the lymphocyte transformation proliferation capability of immunized mice, producing high titers of specific IgG and IgA, suggesting that Δ<italic>pal</italic> possesses good immunogenicity. Challenge protection tests demonstrated that the strain could provide 100% immune protection against wild-type strains in mice.</p></sec><sec id="sec4"><title>Discussion</title><p>This study proves that the <italic>pal</italic> gene influences the virulence of <italic>S. enteritidis</italic>, and Δ<italic>pal</italic> could serve as a candidate strain for attenuated live vaccines, laying the foundation for the development of attenuated live vaccines against <italic>Salmonella</italic>.</p></sec>