Resilience to stress and antibiotics, coupled with immunomodulatory behavior, uncovers Mycobacterium indicus pranii as a suitable surrogate model for tuberculosis research.

Mycobacterium tuberculosis (M.tb) exhibits remarkable adaptability and persistence within host micro-environments, making tuberculosis a persistent global health challenge. Finding safe and relevant model organisms to study M.tb pathobiology is essential for augmenting research in this field. Mycobacterium indicus pranii (MIP), a non-pathogenic mycobacterial species with known immunomodulatory properties and established safety in human applications, represents a promising yet underutilized research model. Within hosts, M.tb encounters diverse stress conditions including oxidative and nitrosative challenges, nutrient limitation, pH fluctuations, and immune cell-mediated pressures, all of which shape its survival strategies. This investigation presents a thorough evaluation of MIP as an alternative research model through systematic comparative analyses with the conventionally utilized Mycobacterium smegmatis (M.smeg). Genomic investigation revealed MIP possesses a significantly higher number of M.tb-homologous virulence-associated genes and conserved drug targets as compared to M. smeg, while sharing equivalent human-homologous gene content with M.tb. Functional assays demonstrated MIP's superior tolerance to multiple stress conditions relevant to host micro-environments, including SDS-mediated envelope stress, nitrosative stress, acidic and alkaline pH extremes, copper toxicity, and elevated temperature-characteristics supported by the presence of key M.tb stress regulator homologs (sigE, sigH, mprAB, and Rv2745c). In macrophage infection models, MIP exhibited enhanced intracellular persistence as compared to M.smeg and induced a balanced cytokine profile resembling M.tb infection. The distinctive genomic and physiological characteristics of MIP establish its biological relevance as a superior surrogate model for investigating mycobacterial stress adaptation mechanisms, virulence determinants, and host-pathogen interactions, potentially accelerating discovery of novel therapeutic strategies against tuberculosis.