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Year : 2019  |  Volume : 3  |  Issue : 3  |  Page : 182-188

Detection of genetic mutations in inh A and kat G for isoniazid and its association with rifampicin resistance in tuberculosis confirmed by line probe assay: Its rationality for isoniazid prophylaxis empirical or drug susceptibility testing guided

State TB Demonstration Cum Training Centre, Intermediate Reference Laboratory, Kolkata, West Bengal, India

Correspondence Address:
Dr. Prasanta Kumar Das
State TB Demonstration Cum Training Centre, Intermediate Reference Laboratory, Kolkata - 700 010, West Bengal
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/bbrj.bbrj_89_19

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Background: The preventive treatment of tuberculosis (TB) is practiced worldwide to execute effective control on its spread. The need for a streamlined definitely structured guideline is realized worldwide. Although there are several guidelines, proper rationale to the use of antibiotics as an effective prophylaxis is yet an area to be discussed. The practice of using an anti-tubercular drug without seeing the resistance pattern and its rationality as a prophylaxis is at the question. Involvement of inhA and kat G in conferring isoniazid (INH) resistance among the rifampicin (RMP) resistant as well as sensitive cases were observed and compared to find out any correlation between resistance of INH and RMP. Moreover, the treatment of drug-resistant TB with the second line of anti-tubercular drugs has been a difficult affair. The revised national TB program advocates INH prophylaxis to the pediatric population who are at an augmented risk of getting the infection from close contacts, without knowing the resistant pattern of the strain of contacts. The study projects the inhA and kat G status among the RMP-resistant adult and pediatric cases. The genetic patterns of INH resistance and their different mutations among isolates of the cases obtained from the adult and pediatric age group of RMP resistance are taken under the study. The point and periodic prevalence is worked out and considered in terms of evaluating the prophylaxis among the probable contacts of the source cases. The guidelines of managing of contacts of multidrug-resistant (MDR) TB and extensively drug-resistant TB patients have little scientific evidence to support and there is lack of national guidelines owing to the discrepancies as is strongly felt.[1] Pediatric contact groups are likely to have latent TB infection (LTBI) that might follow an active TB disease development. Contacts of MDR-TB are considered as LTBI cases. These cases are subjected to preventive therapy.[2] Most of the public health program follows the WHO guideline advocating the use of INH as a prophylaxis irrespective of the resistant status of the source strain. Various national programs advocated administering of a conventional drug as a preventive therapy without actually knowing the susceptibility pattern of the infecting strain of the source case.[3] The selection of a preventive regimen with single or multiple drugs ideally to be based on considering the availability and the bactericidal activity of the primarily infecting strain. Drug-resistant TB among the new and retreatment cases was about 5% in accordance to the surveillance done.[4] The overall proportion of MDR-TB, defined as TB resistant to at least INH and RMP, with or without resistance to other first-line drugs, was 5.3%, ranging from 0% to 35% of reported TB cases.[4] The percentage among the retreatment cases showed a steady rise over the years. The retreatment cases contributed about 20% of MDR-TB among the high TB burden nation.[4] In 2009, only 30,000 (7%) of the 440,000 estimated MDR-TB cases globally were notified, and of them, only 11,000 (3%) were put on treatment known to be consistent with international guidelines.[5] A systematic analysis of the nature of the resistance conferred toward INH may contribute in understanding the common as well as rare genetic alterations. INH resistance is classified as high and low-level resistance based on the minimum inhibitory concentrations. It has been found that the high- and low-level resistance toward INH is associated with the kat G and inh A genes, respectively. Treatment protocols are availed in accordance. The INH resistance is determined in all tubercular cases adult and pediatric irrespective of RMP resistance status, it is found that 92.7% are INH resistant by kat G among RMP-resistant cases. Whereas 17.8% of INH resistance by katG are even among RMP sensitive cases. This relates to a community threat even more after the implication of INH prophylaxis as a part of national program supported by the WHO, and a challenging threat of rising trend of INH resistance is apprehended. Study Design: The study was undertaken at the Intermediate reference laboratory under state TB demonstration cum training center Kolkata, India under revised national TB control program, from April 2012 to December 2016. The study was done among the 442 RMP-resistant isolates recovered from retreatment cases in the year 2012 as well as 627 from newly diagnosed RMP sensitive cases from 2013 to 2016 the study involves a probe into the point and periodic prevalence of INH among the RMP resistant as well as sensitive cases, the most common and rare patterns of genetic mutation that has led to the INH resistance due to inh A as well as kat G among the RMP resistant and sensitive cases. The common and rare codons along with their change in amino acid sequences involved in conferring the resistance were looked for. Methods: The detection of the patterns of genetic mutation is done by the Genotype MTBDR plus V2 kits.(Hains Life Sciences) based on DNA strip technology (Line Probe Assay).[6] Results: Of 442 cases 410 cases showed INH resistance. Out of which exclusive involvement with inhA was seen in 32 cases. Nineteen cases showed involvement of both inh A and kat G. resistance 359 cases accounting to 87.5% showed exclusive involvement of kat G thereby conferring high degree of resistance. The higher percentage of kat G-induced INH resistance among the RMP resistant strains depicts the spread of a higher degree of INH resistance. The question remains how effective would be the INH prophylaxis in pediatric age group in this scenario. The analysis has shown that only around 14.93% of cases reflected exclusive mutations at around 15 and 16 regions of the inhA gene. The presence of both the Wild and mutant gene segments simultaneously (WT and MUT3) accounted to a percentage of 60.3% among the inh A-dependent INH resistance.

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