Abstract

The aim of this study was to investigate the significance of multiple-mutations in the katG gene, predominant nucleotide changes and its correlation with high level of resistance to isoniazid in Mycobacterium tuberculosis isolates that were randomly collected from sputa of 42 patients with primary and secondary active pulmonary tuberculosis from different geographic regions of Iran. Drug susceptibility testing was determined using the CDC standard conventional proportional method. DNA extraction, katG gene amplification and DNA sequencing analysis were performed. Thirty four (80%) isolates were found to have multiple-mutations (composed of 2 - 5 mutations) in the katG gene. Increased number of predominant mutations and nucleotide changes were demonstrated in codons 315 (AGC→ACC), 316 (GGC→AGC), 309 (GGT→GTT) with a higher frequency among patients bearing secondary tuberculosis infection with elevated levels of resistance to isoniazid (MIC µg/ml ≥ 5 - 10). Furthermore it was demonstrated that the combination of mutations with their predominant nucleotide changes were also observed in codons 315, 316 and 309 indicating higher frequencies of mutations among patients with secondary infection respectively. In this study 62% (n = 21) of multi-mutated isolates found to have combination of mutations with predominant nucleotide changes in codons 315 (AGC→ACC), 316 (GGC→GTT), 309 (GGT→GGT) and also demonstrated to be more frequent in isolates of patients with secondary infections, bearing higher level of resistance to isoniazid (≥ 5 – 10 µg/ml). 

Key words: Predominant mutation, Mycobacterium tuberculosis, high level resistant to izoniazid, Iran.