Isoniazid and rifampicin heteroresistant Mycobacterium tuberculosis isolated from tuberculous meningitis patients in India

Background

Heteroresistant Mycobacterium tuberculosis (mixture of susceptible and resistant subpopulations) is thought to be a preliminary stage to full resistance and timely detection, initiation of correct treatment is vital for successful anti tubercular therapy. The aim of this study was to detect multi drug resistant (MDR) and heteroresistant M. tuberculosis with the associated gene mutations from patients of tuberculous meningitis.

Methods

A total of 197 M. tuberculosis isolates from 478 patients of TBM were isolated from July 2012 to July 2015 and subjected to drug susceptibility testing (DST) by BACTEC MGIT and Genotype MTBDR line probe assay (LPA). Heteroresistance was defined as presence of both WT and mutant genes in LPA.

Results

Of 197 M. tuberculosis isolates, 11 (5.6%) were MDR, 23 (11.6%), 1 (0.5%) were mono resistant to isoniazid (INH) and rifampicin (RMP) respectively. Heteroresistance was detected in 8 (4%), 2 (1%) isolates to INH and RMP respectively. INH heteroresistant strains had WT bands with mutation band S315T1 whereas RMP heteroresistant strains had WT bands with mutation band S531L.

Conclusion

The prevalence of MDR M. tuberculosis was 5.6% in TBM patients with the most common mutation being ΔWT band with S315T1 for INH and ΔWT band with S531T for RMP. MGIT DST was found to be more sensitive for detecting overall resistance in M. tuberculosis but inclusion of LPA not only reduced time for early initiation of appropriate treatment but also enabled detection of heteroresistance in 8 (4%), 2 (1%) isolates for INH and RMP respectively.