Ziyi Jia

Metronidazole (MTZ) is an antimicrobial commonly used to treat anaerobic infections. Upon entering anaerobe cells, MTZ is capable of interacting with microbial DNA so that its expression is inhibited. However, what causes susceptibility to MTZ in these anaerobes is largely unknown. Although not an anaerobe, MTZ has been shown to have in vitro bactericidal activity against Mycobacterium tuberculosis (Mtb) under anaerobic conditions, under which Mtb can survive but cannot replicate. MTZ has been discontinued as a drug to treat tuberculosis (TB), an infectious disease Mtb has caused in a quarter of the world’s population, due to its severe side effects. Nonetheless, research subjecting Mtb to MTZ is still useful for identification of microbial genes responsible for susceptibility and resistance to MTZ and possibly other imidazole drugs. In this study, first, killing activities of MTZ on Mtb were characterized. Solid plate cultures of Mycobacterium bovis BCG strains were grown on 7H10 media containing MTZ with concentrations of 0, 25, 50, 100, and 200 μg/mL, respectively. We identified the MBC50 of MTZ when Mtb was subjected to anaerobic killing for 1, 2, and 3 weeks. Resistant mutants were collected from the culture subjected to 3 weeks’ killing with 200 μg/mL of MTZ. The whole genomes of these mutants were sequenced and compared against reference genomes of M. bovis BCG that is susceptible to MTZ in order to identify genes responsible for susceptibility to MTZ.