High frequency of isoniazid and fluroquinolone resistance among patients with rifampicin sensitive tuberculosis.

This study was done to determine frequency of isoniazid (INH) and fluoroquinolones FQ resistance among rifampicin sensitive strains of Mycobacterium tuberculosis and to study their mutation patterns. Retrospective analysis was done for samples with M. tuberculosis detected by Cartridge based NAAT (CBNAAT). They were tested sequentially by first line (FL) and second line - line probe assay (SL-LPA) depending on their drug resistance pattern and following diagnostic algorithm. Total 9722 (74.1 %) of 13124 NAAT positive samples were sensitive for rifampicin. On FL-LPA, 833 (8.6 %) were resistant to INH and of which 110 (13.2 %) were also resistant to FQ by SL-LPA. Most common mutations observed for INH resistance were katG S315T1 mutation in 615 (97.3 %) strains, inhA C15T mutation in 174 (86.6 %) strains and for FQ resistance were gyrA D94G mutation in 46 (41.8 %) strains. Heteroresistance, inferred mutations, combination of mutations and unique mutations were also observed in all genes.

Agreement between CBNAAT, liquid culture and line probe assay for detection of Mycobacterium tuberculosis and anti-tubercular drug resistance in extrapulmonary samples.

PURPOSE: Cartridge based nucleic acid amplification test (CBNAAT) has been endorsed by the WHO as the screening test for diagnosing extrapulmonary tuberculosis (EPTB). In the present study we report the agreement between CBNAAT (Xpert MTB/RIF), liquid culture (LC) and line probe assay (LPA) for diagnosis of Mycobacterium tuberculosis and detection of drug resistance among EPTB cases. METHODS: The EP samples were subjected to CBNAAT (Xpert MTB/RIF, Cepheid, USA) and wherever possible, to LC (MGIT 960, Becton Dickinson, USA) followed sequentially by first line and second line-LPA (FL-LPA, SL-LPA, Hain Lifescience, Germany) on the isolates. RESULTS: Total 566/4080 (13.9%) EP samples were detected positive for M. tuberculosis on CBNAAT. Aspirates from lymph nodes were most often positive (11/30; 36.6%), followed by pus (240/873; 27.5%) and CSF samples (166/104; 15.8%). The detection of M. tuberculosis was more in adults than children except in tissue biopsy samples. Rifampicin resistance was also higher among adults except CSF in which resistance was more in children. Total 185 of 566 (32.7%) CBNAAT positive and 770 of 3510 (21.9%) CBNAAT negative samples could be cultured of which 110/185 (59.4%) and 33/770 (4.3%) respectively turned positive. FL-LPA and SL-LPA of 143 culture isolates showed that 27 isolates had drug resistance, of which 3 (2.1%) were XDR, 11 (7.7%) were Pre-XDR (FQ) and 13 (9.1%) were MDR. Of these 27 resistant isolates, 12 were negative by CBNAAT and two were mislabeled as Rifampicin sensitive or indeterminate based on the unique RpoB gene mutation patterns on LPA. The positive and negative agreements between LC and CBNAAT for detection of M. tuberculosis were 67.1% and 92.7% respectively and between LPA and CBNAAT for rifampicin resistance detection were 98.9% and 92.9% respectively. CONCLUSIONS: For EPTB, CBNAAT should be accompanied with LC wherever possible irrespective of the CBNAAT result.