Ocular Tissue Diagnosis and Drug Susceptibility Testing of Extensively Drug-Resistant Tuberculosis
Sanchita Mitra1, Soumyava Basu1, Somasheila Murthy1, C Sumalatha2, S Sivakumar3
1LV Prasad Eye Institute, Hyderabad, India; 2State TB TDC Hyderabad, India; 3NIRT Chennai, India
Purpose: To report drug susceptibility testing (DST) for different classes of anti-tubercular drugs from ocular samples, during persistent intra-ocular inflammation due to extensively drug resistant tuberculosis (XDR-TB).
Methods: Anterior chamber exudate from a patient with previously diagnosed Rifampicin-resistant TB, was subjected to Ziehl Neelsen (ZN) staining and conventional culture for Mycobacterium tuberculosis. Further, DNA extracted from the sample was tested by reverse hybridization-based second-line line probe assay (slLPA, Genotype MTBDRsl Ver 2.0, Hain Lifescience) . Finally, phenotypic DST on the BACTEC MGIT960 liquid culture system (BD), was performed for the entire panel of anti-TB drugs, including Group A drugs – Bedaquiline and Delanamid, that are not amenable to genotypic DST.
Results: Anterior chamber exudate from the patient revealed acid-fast bacilli on ZN stain of direct smears, and also grew as confluent, non-pigmented colonies on Lowenstein-Jensen media. DNA extracted from the patient sample was positive for the MPB64 gene target of M. tuberculosis, by conventional PCR. slLPA, performed on the extracted DNA, at the state TB reference laboratory revealed the strain to be resistant to the fluoroquinolones Levofloxacin and low dose Moxifloxacin (gyr A mutation), as well as to Amikacin, Kanamycin and Capreomycin (rrs mutation). Phenotypic DST on the BACTEC MGIT960 liquid culture system, showed resistance to all first and second-line ATT including all fluoroquinolones and Linezolid (a Group A drug), thus classifying the infection as XDR-TB, as per current WHO recommendations. The only susceptible drugs for this strain by phenotypic DST were Bedaquiline, Delanamid, Ethionamide, Clofazamine and high-dose Moxifloxacin. The DST results from ocular samples enabled modification of the patient’s anti-TB regimen to include the above susceptible antibiotics. Her systemic symptoms improved dramatically with complete healing of pulmonary lesions and no recurrence till one year follow-up. Her right eye, however, progressed to total corneal melt and had to be eviscerated.
Conclusions: Ocular fluids can potentially be used for both genotypic and phenotypic DST for anti-TB drugs, even in cases where sputum evaluation yields incomplete results. Such determination of drug susceptibility from ocular samples will not only enable appropriate treatment of intraocular TB, but also of systemic TB.
Support: Hyderabad Eye Research Foundation