Surrogate models in pathogenic Mycobacterium research: a systematic review.

Studying pathogenic Mycobacterium spp. (e.g. M. tuberculosis, M. bovis) requires Biosafety Level 3 (BSL-3) laboratories, which limits research opportunities. Safe surrogates that mimic these pathogens are therefore crucial for enabling studies in BSL-1/2 settings and advancing public health. This review examines studies that used the term 'surrogate' in relation to mycobacteria, aiming to identify effective surrogate models and highlight existing research gaps. We categorized the research topics for which surrogates were used, based on the primary goals of each study. Most research focused on Mycobacterial physiology group studies, followed by chemical control, while environmental studies remain largely unexplored. Mycobacterium smegmatis emerged as the most frequently used surrogate, valued for its relatively rapid growth compared to pathogenic Mycobacterium species, along with its genetic tractability and non-pathogenic nature. Mycobacterium marinum, a BSL-2 organism, has contributed to understanding virulence, stress responses and disease modeling. M. bovis BCG has been primarily used in vaccine studies but also appears in drug testing. Surrogate models have advanced our understanding of pathogenic mycobacteria, supporting the development of drugs, vaccines, and diagnostics without the constraints of BSL-3 laboratories. However, limitations remain-particularly in drug screening with M. smegmatis and the underrepresentation of environmental studies. The use of surrogates supports safer, cost-effective research in lower biosafety settings. Expanding ecological research in soil and water and refining model selection are key to improving control strategies.