Cangelosi Gerard A, Do Julie S, Freeman Robert, Bennett John G, Semret Makeda, Behr Marcel A
Seattle Biomedical Research Institute, 307 Westlake Avenue N., Suite 500, Seattle, WA 98109, USA.
Antimicrob Agents Chemother. 2006 Feb;50(2):461-8. doi: 10.1128/AAC.50.2.461-468.2006.
Clinical isolates of the opportunistic pathogen Mycobacterium avium complex (MAC) undergo a reversible switch between red and white colony morphotypes on agar plates containing the lipoprotein stain Congo red. Compared to their isogenic red counterparts, white morphotypic variants are more virulent and more resistant to multiple antibiotics. This report shows that the two-component regulatory system mtrAB is required for the red-to-white switch as well as for other morphotypic switches of MAC. A mutant with a transposon insertion in the histidine protein kinase gene mtrB was isolated from a morphotypically white parent clone. The mutant resembled a naturally occurring red morphotypic variant in that it stained with Congo red, was sensitive to multiple antibiotics, and was permeable by a fluorescent DNA stain. However, it differed from a red variant in that it could not switch to the white or transparent morphotype, and it could not survive intracellularly within macrophage-like cells. Transcomplementation with a cloned wild-type mtrB gene restored to the mutant the ability to form impermeable, drug-resistant white and transparent variants. Quantitative reverse transcriptase PCR showed that mtrB was required for the normal expression of cell surface Mce proteins, some of which are up-regulated in the red-to-white switch. The results indicate that mtrAB functions in regulating the composition and permeability of mycobacterial cell walls and plays a role in the reversible colony type switches of MAC.
机会性病原体鸟分枝杆菌复合群（MAC）的临床分离株在含有脂蛋白染色剂刚果红的琼脂平板上，会在红色和白色菌落形态之间发生可逆转换。与同基因的红色对应菌株相比，白色形态变体的毒性更强，对多种抗生素的耐药性也更强。本报告表明，双组分调节系统mtrAB对于MAC从红色到白色的转换以及其他形态转换是必需的。从形态上为白色的亲本克隆中分离出一个在组氨酸蛋白激酶基因mtrB中插入转座子的突变体。该突变体类似于天然存在的红色形态变体，它能被刚果红染色，对多种抗生素敏感，并且能被荧光DNA染色剂穿透。然而，它与红色变体的不同之处在于，它不能转换为白色或透明形态，并且不能在巨噬细胞样细胞内生存。用克隆的野生型mtrB基因进行反式互补，使突变体恢复了形成不可渗透、耐药的白色和透明变体的能力。定量逆转录聚合酶链反应表明，mtrB对于细胞表面Mce蛋白的正常表达是必需的，其中一些蛋白在从红色到白色的转换中上调。结果表明，mtrAB在调节分枝杆菌细胞壁的组成和通透性方面发挥作用，并在MAC的可逆菌落类型转换中起作用。
