Analysis of katG gene mutations in M tuberculosis isolates by direct sequencing

To understand the mutations of katG gene in M.tuberculosis isolates,and to evaluate their clinical value.Analyzing the katG genes in 92 M.tuberculosis clinical isolates with PCR,PCR SSCP and PCR DS.Mycobacterium tuberculosis strain H37Rv was used as a control. Of 23 drug sensitive isolates,2 displayed abnormal katG SSCP profile.Of 36 non isoniazid resistant isolates,16 had abnormal katG SSCP profile.Of 33 isoniazid resistant isolates,17 were resistant highly to isoniazid,in which 4 katG genes were not amplified and 5 displayed abnormal katG SSCP profile;16 were resistant lowly to isoniazid,in which 13 exhibited abnormal katG SSCP profile.All isolates with abnormal katG SSCP profile had point mutations at codon 315,in which one was AGC→ACC mutation,the others were AGC→AAC mutations .The mutations of katG gene were the most important isoniazid resistant molecular mechanisms in M.tuberculosis.The most common mutations at codon 315 induced the lower MIC for isoniazid.