[Defining of gene mutations and minimal inhibitory concentrations in isoniazid resistant Mycobacterium tuberculosis...

Tuberculosis is a very important disease all over the world despite the advanced diagnostic and treatment regimens. Resistant tuberculosis, which has increased in recent years in particular, is a global problem and prevents the fight against tuberculosis. For this reason, it is important to determine the etiologic agent early and its sensitivity against antituberculosis drugs. Resistance profiles of the isolates and the gene mutations causing resistance are determined for epidemiological purposes and mutation regions of the isolates are being investigated on the basis of countries. The aim of our study was to determine the minimal inhibitor concentration (MIC) of isoniazid (INH) and to investigate the relationship between mutations in resistance genes and MIC values. For this purpose, 25 isoniazid (INH) monoresistant and 25 multidrug resistant (MDR), in total 50 clinical isolates were used and gene mutations causing INH resistance and the relationship of these mutations with minimal inhibitor concentrations (MICs) were searched by GenoType MTBDRplus (Hain Lifescience GMBH, Nehren, Germany) and antibiotic gradient test (E-test, AB BIODISK, Solna, Sweden) methods. The concordance of GenoType MTBDRplus and antibiotic gradient test methods for INH sensitivity, was 88% in INH monoresistant isolates, 80% in MDR isolates and 84% in all isolates. The most frequent mutation zone in INH monoresistant isolates was inhA C15T promotor zone (12 isolates, 54.5%) however, MIC of INH was > 256 µg/ml in two isolates and mutation in katG S315T was observed in both of these isolates. The most frequent mutation zone in MDR isolates was katG S315T (14 isolates, 56%) codon. MIC of INH was > 256 µg/ml in 10 isolates and mutation was observed in katG S315T codon in 5 (50%) isolates, in katG S315T codon and inhA C15T promotor zone in 3 (30%) isolates and in inhA promotor zone in 2 (20%) isolates, respectively. When all the isolates were analyzed, the most frequent mutation was found in katG S315T codon (24 isolates, 48%), MIC of INH was > 256 µg/ml among 12 isolates and the most frequent mutation zone in these isolates which have high MIC for INH was katG S315T codon. In conclusion, the results of this study have shown that the value of MICs for INH is high in isolates with katG S315T mutation, nevertheless, further investigations are needed to support this result.