Veterinary Medicine Post-graduation Program (Animal Pathology), Avian Pathology Laboratory, Department of Pathology, Theriogenology, and One Health, School of Agricultural and Veterinary Sciences, Sao Paulo State University (FCAV/Unesp), Jaboticabal, São Paulo, Brazil; Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen (KU), Copenhagen, Denmark.
Veterinary Medicine Post-graduation Program (Animal Pathology), Avian Pathology Laboratory, Department of Pathology, Theriogenology, and One Health, School of Agricultural and Veterinary Sciences, Sao Paulo State University (FCAV/Unesp), Jaboticabal, São Paulo, Brazil; Department of Preventive Veterinary Medicine, Veterinary School, Federal University of Minas Gerais (UFMG), Belo Horizonte, Minas Gerais, Brazil.
Gene. 2024 Jan 20;892:147827. doi: 10.1016/j.gene.2023.147827. Epub 2023 Sep 23.
Salmonella Gallinarum (SG) provokes fowl typhoid, an infectious disease of acute clinical course that affects gallinaceous of any age and leads to high mortality rates. During the typhoid-like systemic infection of S. Typhimurium (STM) in mice, the bacterium expresses the mgtC gene, which is encoded in the Salmonella Pathogenecity Island - 3 (SPI-3). In this serovar, the function is linked to bacterial replication within macrophages, and its absence attenuates the pathogen. We hypothesized that deleting mgtC from SG genome would alter the microorganism pathogenicity in susceptible commercial poultry in a similar manner. Thus, the present study sought to elucidate the importance of mgtC on SG pathogenicity. For this, a mgtC-mutant lacking S. Gallinarum mutant was constructed (SG ΔmgtC). Its ability to replicate in medium that mimicries the mgtC-related intracellular environment of macrophages as well as in primary macrophages from chicken was evaluated. Moreover, the infection of susceptible chickens was performed to elucidate its pathogenicity and the elicited immune responses by measuring key interleukins by qRT-PCR and the population of macrophages and lymphocytes T CD4 and CD8 by means of immunohistochemistry. It was observed that mgtC was required for S. Gallinarum replication in acidified low-Mg media and survival within macrophages. However, unlike its requirement for initial phase of STM infection in mice, lower bacterial counts were only observed at the late stage of macrophage infection without affecting the citotoxicity. Experiments showed that knocking-out the mgtC gene neither altered bacterial uptake by macrophages nor affects bacterial counts in liver and spleen and total chicken mortality. However, plotting a survival curve and analyzing the clinical-pathologic conditions, it was observed a slower progression of the disease in chickens infected by SG ΔmgtC compared to those challenged by the wild-type strain. Furthermore, the mRNA expression of IFN-γ and LITAF were similar between the infected chickens, but higher than in the uninfected group. The same was observed in macrophages and lymphocytes T CD4 populations. On the other hand, the presence of lymphocytes T CD8 was increased in the initial phase of the disease provoked by the wild-type strain over the mutant strain. We concluded that the role of mgtC in Fowl Typhoid in susceptible chickens differs from the role in typhoid-like infections in mammals. Thus, the deletion of mgtC gene from S. Gallinarum genome does not affect the overall pathogenicity, but slightly alters the pathogenesis.
鸡白痢沙门氏菌（SG）引起家禽伤寒，这是一种急性临床病程的传染病，可影响任何年龄的家禽，导致高死亡率。在鼠伤寒沙门氏菌（STM）的伤寒样全身感染中，细菌表达 mgtC 基因，该基因编码在沙门氏菌致病性岛 - 3（SPI-3）中。在该血清型中，该功能与巨噬细胞内细菌的复制有关，其缺失会减弱病原体。我们假设从 SG 基因组中删除 mgtC 会以类似的方式改变易感商业家禽中的微生物致病性。因此，本研究旨在阐明 mgtC 对 SG 致病性的重要性。为此，构建了缺乏 S. Gallinarum 突变体的 mgtC 突变体（SG ΔmgtC）。评估了其在模拟巨噬细胞中与 mgtC 相关的细胞内环境的培养基以及鸡原代巨噬细胞中的复制能力。此外，通过测量 qRT-PCR 关键白细胞介素的水平和通过免疫组织化学测量巨噬细胞和淋巴细胞 T CD4 和 CD8 的数量，进行了易感鸡的感染实验，以阐明其致病性和诱导的免疫反应。结果表明，mgtC 是 SG 在酸化低镁培养基中的复制和在巨噬细胞内生存所必需的。然而，与 STM 在小鼠感染的初始阶段的要求不同，仅在巨噬细胞感染的晚期观察到细菌计数较低，而不影响细胞毒性。实验表明，敲除 mgtC 基因既不会改变巨噬细胞对细菌的摄取，也不会影响肝脏和脾脏以及总鸡死亡率的细菌计数。然而，绘制生存曲线并分析临床病理情况时，与野生型菌株相比，感染 SG ΔmgtC 的鸡的疾病进展较慢。此外，感染鸡的 IFN-γ 和 LITAF 的 mRNA 表达相似，但高于未感染组。在巨噬细胞和淋巴细胞 T CD4 群体中也是如此。另一方面，在野生型菌株引起的疾病的初始阶段，淋巴细胞 T CD8 的存在增加，而在突变菌株中则没有。我们得出结论，mgtC 在易感鸡中的家禽伤寒中的作用与哺乳动物中的伤寒样感染中的作用不同。因此，从 SG 基因组中删除 mgtC 基因不会影响整体致病性，但会稍微改变发病机制。
