Association Between the Phenotype and Genotype of Isoniazid Resistance Among Mycobacterium tuberculosis Isolates in Thailand

Ratchanu Charoenpak, 1 Wichai Santimaleeworagun, 2 Gompol Suwanpimolkul, 3–5 Weerawat Manosuthi, 6 Paweena Kongsanan, 6 Suthidee Petsong, 7 Chankit Puttilerpong 8 1College of Pharmacotherapy Thailand, Nonthaburi, Thailand; 2Department of Pharmacy, Faculty of Pharmacy, Silpakorn University, Nakhon Pathom, Thailand; 3Department of Medicine, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand; 4Tuberculosis Research Unit, Chulalongkorn University, Bangkok, Thailand; 5Emerging Infectious Diseases Clinical Center, Thai Red Cross, Bangkok, Thailand; 6Bamrasnaradura Infectious Diseases Institute, Ministry of Public Health, Nonthaburi, Thailand; 7Department of Microbiology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand; 8Department of Pharmacy Practice, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok, ThailandCorrespondence: Chankit PuttilerpongDepartment of Pharmacy Practice, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Phayathai Road, Patumwan, Bangkok, ThailandTel|Fax +66 2 218 8403Email Chankit.P@chula.ac.thPurpose: The emergence of isoniazid-resistant tuberculosis (HR-TB) is a global public health problem, causing treatment failure and high mortality rates. This study aimed to determine the minimal inhibitory concentration (MIC) of isoniazid and detect the gene mutation in HR-TB and any association between the level of isoniazid resistance and gene mutation.Methods: We collected 74 clinical HR-TB isolates from two tertiary-care centers in Thailand. MICs were established using broth macrodilution. A line probe assay (LPA) was used to detect gene mutations that confer resistance to isoniazid, rifampicin, aminoglycosides, and fluoroquinolones.Results: Sixty-one (82.4%) isolates were monoresistant to isoniazid and 44 (72.1%) were highly resistant to isoniazid. From the clinical isolates, the range of isoniazid MICs was 0.4– 16 μg/mL. The katG S315T gene mutation was the prominent mutation in both isoniazid-monoresistant TB (70.5%) and multidrug-resistant TB (72.7%) isolates. The positive predictive value (PPV) of katG was 100% in detecting high levels of isoniazid resistance. The PPV of the inhA mutation was 93.8% in detecting low levels of isoniazid resistance. Five isolates (6.8%) exhibited low-level phenotypic resistance, whereas an LPA failed to detect an isoniazid gene mutation. Our study found one HR-TB isolate with a gyrA fluoroquinolone-resistant gene mutation.Conclusion: Most HR-TB isolates had high isoniazid-resistance levels associated with the katG gene mutation. High-dose isoniazid should be used with caution in patients with HR-TB. Early detection of drug resistance by genotypic assay can help determine an appropriate regimen.Keywords: tuberculosis, isoniazid, minimal inhibitory concentration, line probe assay, gene mutation