Université Montpellier I, Centre d’études d’agents Pathogènes et Biotechnologies pour la Santé, Montpellier, France.
J Infect Dis. 2012 Nov;206(9):1424-32. doi: 10.1093/infdis/jis522. Epub 2012 Aug 28.
Genome analysis indicated that the new species Brucella microti possesses a potentially functional glutamate decarboxylase (GAD) system involved in extreme acid resistance in several foodborne bacteria. The contribution of this system in adaptation of B. microti to an acidic environment, including the intracellular vacuole and stomach, was investigated.
B. microti was GAD positive and able to export its product, γ-aminobutyrate, to the extracellular medium. The resistance of B. microti to acid stress (pH 2.5) was glutamate dependent. Mutants affected in the GAD system lost this resistance, demonstrating its direct involvement in survival under these conditions. The reciprocal heterologous complementation of mutants with the GAD systems of Escherichia coli or B. microti confirmed conserved functions in both bacterial species. A gad mutant was not attenuated during infection of macrophages, where Brucella resides in an acidified vacuole at a pH of 4-4.5 during the early phase of macrophage infection, but GAD contributed to the survival of B. microti in a murine model following oral infection.
This work provides first evidence that the GAD system might play an essential role in the resistance of an environment-borne, pathogenic Brucella species to extreme acid shock and during passage through the host stomach following oral infection.
基因组分析表明，新物种布鲁氏菌 microti 拥有一个潜在功能的谷氨酸脱羧酶 (GAD) 系统，该系统涉及几种食源性病原体的极端耐酸能力。本研究旨在探究该系统在布鲁氏菌 microti 适应酸性环境（包括细胞内空泡和胃部）中的作用。
布鲁氏菌 microti 为 GAD 阳性，能够将其产物γ-氨基丁酸分泌到细胞外培养基中。布鲁氏菌 microti 对酸应激（pH 2.5）的抗性依赖于谷氨酸。GAD 系统突变体丧失了这种抗性，表明其直接参与了这些条件下的存活。用大肠杆菌或布鲁氏菌 microti 的 GAD 系统对突变体进行的反向异源互补实验证实了这两个细菌物种中该系统的保守功能。在巨噬细胞感染过程中，gad 突变体并未减弱，因为在巨噬细胞感染的早期阶段，布鲁氏菌存在于酸化的空泡中，pH 值为 4-4.5，但 GAD 有助于布鲁氏菌 microti 在口服感染后的小鼠模型中存活。
本研究首次证明，GAD 系统可能在环境传播的致病性布鲁氏菌抵抗极端酸冲击以及在口服感染后通过宿主胃的过程中发挥重要作用。
