Genetic Polymorphism at Codon 463 in the katG Gene in Isoniazid-Sensitive and -Resistant Isolates of Mycobacterium tuberculosis from the Middle East

Abstract

Objective: To determine whether substitution R463L within the katG gene is associated with resistance to isoniazid in clinical isolates of Mycobacterium tuberculosis recovered from tuberculosis (TB) patients from the Middle East. Methods: A total of 113 clinical isolates of M. tuberculosis obtained from TB patients residing in Kuwait, UAE and Lebanon were used. The isolates were characterized as isoniazid-susceptible (n = 25) or -resistant (n = 88) based on drug susceptibility testing by BACTEC 460 TB system. The presence of R463L mutation within the katG gene of each isolate was detected by amplification of the DNA region around codon 463 by polymerase chain reaction (PCR) followed by digestion with restriction endonuclease NciI to generate PCR-restriction fragment length polymorphism. The results with selected isolates were further confirmed by DNA sequencing. Results: The mutation R463L was detected in 46 of 59 isoniazid-resistant clinical M. tuberculosis isolates from Kuwait, 9 of 12 from UAE and 3 of 17 from Lebanon. The prevalence of this substitution was much higher in isolates recovered from patients of South Asian/Southeast Asian origin (41/49, 84%) than from patients of Middle Eastern origin (17/39, 44%). Although all the 7 isoniazid-susceptible isolates of M. tuberculosis from Lebanon (recovered exclusively from Middle Eastern patients) contained arginine at codon 463, 3/7 and 10/11 isoniazid-susceptible strains from Kuwait, recovered from Middle Eastern and South Asian patients, respectively, contained leucine at codon 463. Conclusion: The results show that genetic polymorphism exists at codon 463 in the katG gene of M. tuberculosis recovered from patients of different ethnic backgrounds. The data also show that substitution R463L within the katG gene does not contribute to isoniazid resistance.