Department of Veterinary Infectious Diseases and Avian Diseases, College of Veterinary Medicine and Center for Poultry Diseases Control, Jeonbuk National University, Iksan, South Korea.
Bio Disease Control(BIOD) Co., Ltd., Iksan, Republic of Korea.
PLoS One. 2020 Sep 10;15(9):e0238630. doi: 10.1371/journal.pone.0238630. eCollection 2020.
Salmonella enterica serovar Gallinarum (S. Gallinarum) can cause fowl typhoid, a severe systemic disease responsible for considerable economic losses. Chicken pathogenicity test is the traditional method for assessing the virulence of S. Gallinarum. However, this method is limited by several factors, including ethical considerations, costs, and the need for specialized facilities. Hence, we established a chicken embryo lethality assay (ELA) model to determine the virulence of S. Gallinarum. Three virulent and three avirulent representative strains, which were confirmed by the chicken pathogenicity test, were used to perform the ELA. The most significant difference between the virulent and avirulent strains could be observed when 13-day-old embryos were inoculated via the AC route and incubated for 5 days. Based on a 50% embryo lethal dose (ELD50), isolates considered to be virulent had a Log10ELD50 of ≤ 4.0, moderately virulent strains had a Log10ELD50 of 4.0-6.1, and avirulent isolates had a Log10ELD50 of ≥ 6.1. Different abilities to invade the liver of embryos were found between the virulent and avirulent strains by a growth curve experiment in vitro. The maximum colony-forming units (CFU) of the virulent strain was about 10,000 times higher than that of the avirulent strain in the liver at 5 days post infection. The ELA results of 42 field strains showed that thirty-two strains (76.2%) were virulent, nine were moderately virulent (21.4%), and one strain was avirulent (2.4%). In conclusion, these results suggest that the ELA can be used as an alternative method to assess the virulence of S. Gallinarum, which will contribute to the study of virulence genes, virulence evolution, pathogenic mechanisms and vaccine development.
鸡白痢沙门氏菌（S. Gallinarum）可引起禽伤寒，这是一种严重的全身性疾病，会导致巨大的经济损失。鸡致病性试验是评估 S. Gallinarum 毒力的传统方法。然而，这种方法受到多种因素的限制，包括伦理考虑、成本和对专门设施的需求。因此，我们建立了鸡胚致死率测定（ELA）模型来确定 S. Gallinarum 的毒力。使用经过鸡致病性试验证实的 3 株强毒株和 3 株弱毒株进行 ELA。在通过 AC 途径接种 13 日龄胚胎并孵育 5 天后，可观察到强毒株和弱毒株之间最显著的差异。根据 50%胚胎致死剂量（ELD50），被认为是强毒力的分离株的 Log10ELD50≤4.0，中度毒力菌株的 Log10ELD50 为 4.0-6.1，而弱毒力分离株的 Log10ELD50≥6.1。通过体外生长曲线实验发现，强毒株和弱毒株在胚胎肝脏中的侵袭能力不同。在感染后 5 天，强毒株在肝脏中的最大集落形成单位（CFU）约是弱毒株的 10000 倍。42 株田间分离株的 ELA 结果显示，32 株（76.2%）为强毒力，9 株为中度毒力（21.4%），1 株为弱毒力（2.4%）。总之，这些结果表明，ELA 可以作为评估 S. Gallinarum 毒力的替代方法，这将有助于毒力基因、毒力进化、致病机制和疫苗开发的研究。
