ABSTRACT
Isoniazid resistant mechanisms in Mycobacterium tuberculosis have been shown to involve at least two genes, kat G and inh A. Alteration in the kat G gene has been found in a great number of resistant isolates. Percentage of resistant isolates harboring alteration in this gene varied among laboratories suggesting that different mutations were presented in different geographic areas. Fourteen isoniazid resistant and five multidrug resistant isolates from the Central Chest Hospital, Thailand, were examined for the kat G gene mutations in the region between base position 17 to 299. No different pattern of mutations were found between these two groups. Among nineteen isolates, there were nine isolates which showed point mutations and five isolates with base insertions of the kat G gene. The remaining five isolates revealed gene deletion. Heteroduplex formation technique also confirmed base alterations in these nine mutants.