Equine Infectious Disease Laboratory, Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, TX, 77843-4475, United States.
Image Analysis Laboratory, Department of Veterinary Integrative Biosciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, TX, 77843-4458, United States.
Vet Microbiol. 2021 Jun;257:109069. doi: 10.1016/j.vetmic.2021.109069. Epub 2021 Apr 10.
Rhodococcus equi is a soil saprophytic bacterium and intracellular pathogen that causes pneumonia in foals. Strains of R. equi that are virulent in foals contain a plasmid that encodes a virulence-associated protein A (VapA) necessary for replication in macrophages. Because other intracellular pathogens survive and replicate inside amoebae, we postulated that the VapA-bearing plasmid (pVAPA) confers a survival advantage for R. equi against environmental predators like amoebae. To test this hypothesis, we compared phagocytosis by and survival in Acanthamoeba castellanii of isogenic strains of pVAPA-positive and pVAPA-negative R. equi. Phagocytosis of the pVAPA-negative strain by A. castellanii was significantly (P < 0.0001) greater than the pVAPA-positive strain. Intracellular replication of the pVAPA-positive strain in A. castellanii was significantly (P < 0.0001) greater than the pVAPA-negative strain during both 48 h and 9 days. These results indicate that the presence of the VapA plasmid reduces uptake and aids replication of R. equi in A. castellanii.
马红球菌是一种土壤腐生菌和细胞内病原体，可引起驹肺炎。在驹中具有毒力的马红球菌菌株含有编码一种毒力相关蛋白 A（VapA）的质粒，该蛋白对于在巨噬细胞中复制是必需的。由于其他细胞内病原体在变形虫体内存活和复制，我们推测携带 VapA 的质粒（pVAPA）赋予了马红球菌抵御变形虫等环境捕食者的生存优势。为了验证这一假说，我们比较了具有和不具有 pVAPA 的马红球菌同源菌株在粘菌（Acanthamoeba castellanii）中的吞噬作用和存活情况。粘菌对 pVAPA 阴性菌株的吞噬作用明显（P < 0.0001）大于 pVAPA 阳性菌株。在 48 小时和 9 天内，pVAPA 阳性菌株在粘菌中的细胞内复制明显（P < 0.0001）大于 pVAPA 阴性菌株。这些结果表明，VapA 质粒的存在减少了马红球菌在粘菌中的摄取并有助于其复制。
