Instituto de Salud Tropical (ISTUN), Instituto de Investigación Sanitaria de Navarra (IdiSNA) and Dpto. de Microbiología y Parasitología, Universidad de Navarra, c/Irunlarrea 1, 31008, Pamplona, Spain.
Unidad de Producción y Sanidad Animal, Centro de Investigación y Tecnología Agroalimentaria de Aragón (CITA), Avda. Montañana 930, 50059, Zaragoza, Spain.
Vet Res. 2020 Jul 23;51(1):92. doi: 10.1186/s13567-020-00815-8.
Brucella is a genus of gram-negative bacteria that cause brucellosis. B. abortus and B. melitensis infect domestic ruminants while B. suis (biovars 1-3) infect swine, and all these bacteria but B. suis biovar 2 are zoonotic. Live attenuated B. abortus S19 and B. melitensis Rev1 are effective vaccines in domestic ruminants, though both can infect humans. However, there is no swine brucellosis vaccine. Here, we investigated the potential use as vaccines of B. suis biovar 2 rough (R) lipopolysaccharide (LPS) mutants totally lacking O-chain (Bs2ΔwbkF) or only producing internal O-chain precursors (Bs2Δwzm) and mutants with a smooth (S) LPS defective in the core lateral branch (Bs2ΔwadB and Bs2ΔwadD). We also investigated mutants in the pyruvate phosphate dikinase (Bs2ΔppdK) and phosphoenolpyruvate carboxykinase (Bs2ΔpckA) genes encoding enzymes bridging phosphoenolpyruvate and the tricarboxylic acid cycle. When tested in the OIE mouse model at the recommended R or S vaccine doses (10 and 10 CFU, respectively), CFU/spleen of all LPS mutants were reduced with respect to the wild type and decreased faster for the R than for the S mutants. At those doses, protection against B. suis was similar for Bs2ΔwbkF, Bs2Δwzm, Bs2ΔwadB and the Rev1 control (10 CFU). As described before for B. abortus, B. suis biovar 2 carried a disabled pckA so that a double mutant Bs2ΔppdKΔpckA had the same metabolic phenotype as Bs2ΔppdK and ppdK mutation was enough to generate attenuation. At 10 CFU, Bs2ΔppdK also conferred the same protection as Rev1. As compared to other B. suis vaccine candidates described before, the mutants described here simultaneously carry irreversible deletions easy to identify as vaccine markers, lack antibiotic-resistance markers and were obtained in a non-zoonotic background. Since R vaccines should not elicit antibodies to the S-LPS and wzm mutants carry immunogenic O-chain precursors and did not improve Bs2ΔwbkF, the latter seems a better R vaccine candidate than Bs2Δwzm. However, taking into account that all R vaccines interfere in ELISA and other widely used assays, whether Bs2ΔwbkF is advantageous over Bs2ΔwadB or Bs2ΔppdK requires experiments in the natural host.
布鲁氏菌是一种革兰氏阴性细菌属，可引起布鲁氏菌病。B. abortus 和 B. melitensis 感染家养反刍动物，而 B. suis（生物型 1-3）感染猪，除了 B. suis 生物型 2 外，所有这些细菌都具有人畜共患性。活减毒的 B. abortus S19 和 B. melitensis Rev1 是家养反刍动物有效的疫苗，尽管两者都可能感染人类。然而，目前没有猪布鲁氏菌病疫苗。在这里，我们研究了 B. suis 生物型 2 粗糙（R）脂多糖（LPS）突变体作为疫苗的潜力，这些突变体完全缺乏 O-链（Bs2ΔwbkF）或仅产生内部 O-链前体（Bs2Δwzm），以及 LPS 核心侧支缺陷的光滑（S）突变体（Bs2ΔwadB 和 Bs2ΔwadD）。我们还研究了丙酮酸磷酸二激酶（Bs2ΔppdK）和磷酸烯醇丙酮酸羧激酶（Bs2ΔpckA）基因的突变体，这些基因编码连接磷酸烯醇丙酮酸和三羧酸循环的酶。在 OIE 小鼠模型中，按照推荐的 R 或 S 疫苗剂量（分别为 10 和 10 CFU）进行测试时，与野生型相比，所有 LPS 突变体的脾 CFU 均减少，且 R 突变体比 S 突变体减少得更快。在这些剂量下，Bs2ΔwbkF、Bs2Δwzm、Bs2ΔwadB 和 Rev1 对照（10 CFU）对 B. suis 的保护作用相似。如前所述，B. suis biovar 2 携带失活的 pckA，因此双突变体 Bs2ΔppdKΔpckA 具有与 Bs2ΔppdK 相同的代谢表型，并且 ppdK 突变足以产生衰减。在 10 CFU 时，Bs2ΔppdK 也与 Rev1 一样提供相同的保护。与以前描述的其他 B. suis 疫苗候选物相比，这里描述的突变体同时携带易于识别的不可逆缺失，作为疫苗标记物，缺乏抗生素抗性标记物，并在非人畜共患病背景下获得。由于 R 疫苗不应引起对 S-LPS 的抗体反应，并且 wzm 突变体携带免疫原性 O-链前体，并且不能改善 Bs2ΔwbkF，因此后者似乎是比 Bs2Δwzm 更好的 R 疫苗候选物。然而，考虑到所有 R 疫苗都会干扰 ELISA 和其他广泛使用的检测，Bs2ΔwbkF 是否优于 Bs2ΔwadB 或 Bs2ΔppdK 需要在自然宿主中进行实验。
