Diversity of glpK Gene and Its Effect on Drug Sensitivity in Mycobacterium bovis

BACKGROUND: Glycerol kinase (glpK) is essential for the first step of glycerol catabolism in Mycobacterium tuberculosis. However, Mycobacterium bovis has been known to grow poorly in glycerol media because of a base insertion in the glpK gene. METHODS: We analyzed the glpK gene sequences of 60 clinical M. bovis isolates, and determined the minimum inhibitory concentration of 14 drugs by microdilution method to evaluate the effect of frameshift mutations on drug sensitivity. The effect of M. bovis growth rate on its drug sensitivity was investigated using bacteria grown on glycerol or pyruvate. RESULTS: A total of 44 (73.33%) clinical M. bovis isolates have frameshift mutations in a homopolymeric tract of 7 cytosines in the glpK gene. 15.00% M. bovis isolates showed phenotypic drug resistance. Glycerol metabolism-deficient M. bovis showed reduced susceptibility to 9 out of 14 tested drugs. Mutations in the glpK gene can lead to impaired growth in glycerol-based media, while the minimal inhibitory concentration values of slow-growing M. bovis were higher. CONCLUSION: Mutations in the glpK gene can lead to slowed growth and reduced susceptibility to drugs in M. bovis, which may contribute to the emergence of drug-resistant M. bovis and pose a threat to human health owing to the zoonotic capacity of M. bovis.