l-Alanine specifically potentiates fluoroquinolone efficacy against Mycobacterium persisters via increased intracellular reactive oxygen species

Tuberculosis caused by Mycobacterium tuberculosis remains a major global health concern; M. tuberculosis drug resistance and persistence further fueled the situation. Nutrient supportive therapy was intensively pursued to complement the conventional treatment, as well as their synergy with current antibiotics. To explore whether l-alanine can synergize with fluoroquinolones against M. tuberculosis, M. smegmatis was used as a surrogate in this study. We found that l-alanine can boost the bactericidal efficacy of fluoroquinolones, increasing the production of intracellular reactive oxygen species. This effect is very significant for persisters. Accelerated tricarboxylic acid cycle and/or nucleotide metabolism were observed after the addition of l-alanine. M. smegmatis MSMEG2660 is a homolog of the alanine dehydrogenase (Rv2780, MSMEG2659) negative regulator Rv2779c and involved in the l-alanine potentiation of fluoroquinolone via funneling more alanine into tricarboxylic acid. Deletion mutant of the MSMEG2660 ( increment Ms2660) became more susceptible, and more readily revived from persistence. We firstly found that l-alanine can synergize with fluoroquinolones against Mycobacterium, especially the persisters via promoting metabolism. This will inspire new avenue to eliminate Mycobacterium persisters.