Abstract / Summary
Differentiation of Mycobacterium tuberculosis complex (MTBC) species is essential for appropriate treatment and epidemiological surveillance, particularly due to intrinsic pyrazinamide resistance in M. bovis and the zoonotic potential of M. orygis . However, no published data are available on the species distribution of MTBC in Kerala, India. We have conducted a retrospective study of 239 archived MTBC clinical isolates collected between 2017 and 2024 at a tertiary care centre in Kerala. Species identification was performed using gyrB PCR-restriction fragment length polymorphism (PCR-RFLP). RD1 and RD4 PCR assays were used to distinguish M. bovis BCG from wild-type M. bovis . In silico analysis was performed to identify a gyrB single nucleotide polymorphism enabling specific detection of M. orygis . Of the 239 isolates, 232 (97.1%) were identified as M. tuberculosis and 7 (2.9%) as M. bovis BCG. No wild-type M. bovis or M. orygis isolates were identified among the 239 isolates tested in this cohort. Four BCG isolates were recovered from vaccinated children, including three infants and one 4-year-old child, and three from patients who had received intravesical BCG therapy for bladder carcinoma. M. tuberculosis was the predominant MTBC species in this cohort. Although zoonotic MTBC species were not identified, detection of M. bovis BCG, including cases with disseminated disease, highlights the importance of species-level diagnosis to guide treatment and recognise vaccine-associated disease.