Phthiocerol dimycocerosate (PDIM) is an essential virulence lipid of Mycobacterium tuberculosis. In vitro culturing rapidly selects for spontaneous PDIM-negative mutants that have attenuated virulence and increased cell wall permeability, thus impacting the relevance of experimental findings. PDIM loss can also reduce the efficacy of the BCG Pasteur vaccine. Here we show that vancomycin susceptibility can rapidly screen for M. tuberculosis PDIM production. We find that metabolic deficiency of methylmalonyl-CoA impedes the growth of PDIM-producing bacilli, selecting for PDIM-negative variants. Supplementation with odd-chain fatty acids, cholesterol or vitamin B₁₂ restores PDIM-positive bacterial growth. Specifically, we show that propionate supplementation enhances PDIM-producing bacterial growth and selects against PDIM-negative mutants, analogous to in vivo conditions. Our study provides a simple approach to screen for and maintain PDIM production, and reveals how discrepancies between the host and in vitro nutrient environments can attenuate bacterial pathogenicity.

Phthiocerol dimycocerosate (PDIM) 是结核分枝杆菌的必需毒力脂质。体外培养快速选择自发的 PDIM 阴性突变体，这些突变体的毒力减弱，细胞壁通透性增加，从而影响实验结果的相关性。 PDIM 丢失也会降低 BCG 巴斯德疫苗的功效。在这里，我们表明万古霉素敏感性可以快速筛查结核分枝杆菌PDIM 的产生。我们发现甲基丙二酸单酰辅酶A的代谢缺陷会阻碍产生PDIM的杆菌的生长，从而选择PDIM阴性变体。补充奇数链脂肪酸、胆固醇或维生素 B ₁₂可恢复 PDIM 阳性细菌的生长。具体来说，我们表明补充丙酸可以增强产生 PDIM 的细菌生长，并选择针对 PDIM 阴性突变体，类似于体内条件。我们的研究提供了一种筛选和维持 PDIM 产生的简单方法，并揭示了宿主和体外营养环境之间的差异如何减弱细菌致病性。