Fourteen of 22 (68%) Mycobacterium bovis strains isolated from cattle in Sa
rdinia were found to be resistant to rifampin and isoniazid, Analysis of th
e rpoB and the katG, oxyR-ahpC, and inhA gene regions of these strains was
performed in order to investigate the molecular basis of rifampin and isoni
azid resistance, respectively. The most frequent mutation, encountered in 6
of 10 strains (60%), was in the rpoB gene; it occurred, at codon position
521 and resulted in leucine changed to proline, This suggests that codon 52
1 may be important for the development of rifampin resistance in M, bovis.
Resistance to isoniazid is associated in Mycobacterium tuberculosis with a
variety of mutations affecting one or more genes. Our results confirm the d
ifficulty of interpreting the sequence variations observed in clinical stra
ins of M, bovis. M. bovis strains isolated from the same geographic area sh
owed similar mutations within the genes responsible for rifampin and isonia
zid resistance. Our results represent the first study to elucidate the mole
cular genetic basis of drug resistance in M. bovis isolated from cattle.