Variations in the occurrence of the S315T mutation within the katG gene in isoniazid-resistant clinical Mycobacterium tuberculosis isolates from Kuwait.

The worldwide threat of drug-resistant tuberculosis (TB) to human health has led to the development of molecular methods for rapidly determining the resistance of clinical Mycobacterium tuberculosis isolates to the two front-line antituberculous drugs, isoniazid and rifampin. The prevalence of the S315T mutation within the katG gene, which confers clinically significant resistance to isoniazid, was determined in isoniazid-resistant clinical M. tuberculosis isolates recovered from TB patients in Kuwait. A total of 67 isoniazid-resistant and 18 susceptible clinical M. tuberculosis isolates were tested. The mutation S315T was found in 46 (69%) of the 67 resistant strains, whereas none of the susceptible strains contained this mutation. The prevalence of this mutation was highest (32 of 40, 80%) in isolates recovered from patients of South Asian origin and lowest in isolates from patients of Middle Eastern origin (8 of 18, 44%). The genotyping performed on isolates carrying the S315T mutation showed that the isolates belong to several different types as they exhibited unique DNA banding patterns. The results point to a varying prevalence of the S315T mutation within the katG gene in clinical M. tuberculosis isolates recovered from patients of different ethnic groupings within the same country. The results also suggest that detection of the S315T mutation in the katG gene may be used as a rapid screening method for identifying isoniazid-resistant clinical M. tuberculosis isolates recovered from majority of patients in some ethnic groupings.