Propionate prevents loss of the PDIM virulence lipid in Mycobacterium tuberculosis

Area of Science:

• Microbiology
• Biochemistry
• Immunology

Background:

• Phthiocerol dimycocerosate (PDIM) is a key virulence lipid in Mycobacterium tuberculosis.
• Loss of PDIM in vitro leads to attenuated virulence and reduced BCG vaccine efficacy.
• In vitro culture conditions can inadvertently select for PDIM-deficient mutants.

Purpose of the Study:

• To develop a method for screening and maintaining PDIM production in M. tuberculosis.
• To understand how nutrient availability affects PDIM synthesis and bacterial growth.
• To improve the relevance of in vitro studies on M. tuberculosis.

Main Methods:

• Utilizing vancomycin susceptibility as a rapid screen for PDIM production.
• Investigating the role of methylmalonyl-CoA metabolism in PDIM synthesis.
• Supplementing bacterial cultures with odd-chain fatty acids, cholesterol, or vitamin B12.
• Testing propionate supplementation to restore PDIM-positive growth.

Main Results:

• Vancomycin susceptibility effectively screens for PDIM production in M. tuberculosis.
• Metabolic deficiency in methylmalonyl-CoA favors PDIM-negative variants.
• Supplementation with odd-chain fatty acids, cholesterol, or vitamin B12 restores growth of PDIM-producing strains.
• Propionate supplementation specifically enhances PDIM-producing bacterial growth and selects against PDIM-negative mutants.

Conclusions:

• A simple method using vancomycin susceptibility can screen for and maintain PDIM production.
• Nutrient availability significantly impacts M. tuberculosis PDIM synthesis and pathogenicity.
• Discrepancies between host and in vitro environments can attenuate bacterial virulence.