Table 1.
Bacterial strains and plasmids used in this study.
Table 2.
Oligonucleotide primers used in this study.
Table 3.
Determination of LD50 in CD1 mice infected with the WT GD01, ΔssnA, and C-ΔssnA strains.
Fig 1.
Construction of the ΔssnA mutant strain and complementation strain.
(A) Schematic of the strategy for the ssnA gene deletion in the SS2 GD01 strain via double-crossover recombination. The plasmid pSET4sΔssnA is used for the ssnA gene knockout. (B) PCR confirmation of the mutant strain. (C) Growth of the WT GD01, ΔssnA mutant, and its complementation.
Fig 2.
The WT, ΔssnA, and C-ΔssnA strains adhere to and invade (A), and invasion of (B) Hep-2 cells after 2 h of infection. The data are means and SD of three independent experiments, **P < 0.01.
Fig 3.
Detection of the WT, ΔssnA, and C-ΔssnA strains invasion in blood and tissues.
Blood (A), spleens (B), livers (C), and brains (D) were collected from infected CD1 mice and homogenized at 3, 5, and 7 days after infection.
Fig 4.
The CI of ΔssnA against the WT strain in vivo.
Six CD1 mice were infected i.p. with ΔssnA: WT at 1:1 ratio. At 8 h post inoculation, the value of CI in blood samples was calculated.
Fig 5.
Production of SS2-specific IgG antibodies in immunized mice.
The CD1 mice were immunized with SS2 inactive vaccine, ΔssnA, or PBS, and antibody levels were detected at 14, and 28 days post-inoculation by indirect ELISA. The data are expressed as the mean ± SD, *P < 0.05 and **P < 0.01. Δ, versus the negative control.
Fig 6.
The cellular immune responses induced in immunized mice.
(A) Splenocytes from immunized mice were collected at 28 day post-first immunization and lymphocyte proliferation assay was evaluated using a cell proliferation kit with MTT reagent. (B) Production of cytokines in stimulated splenocytes was detected by ELISA. *P < 0.05. Δ, versus the negative control.
Fig 7.
Survival curves of mice challenged with a high-virulent SS2 strain.