DOAJ
Phenotypic Identification of Non - Tuberculosis Mycobacterium Isolated from Clinical Samples
By Ms Roshini, Divya Suguna Jayakar, Uma Makeshwari and 1 others.
Abstract
Background
Non-tuberculous mycobacteria (NTM) are increasingly recovered from clinical specimens in high tuberculosis-burden settings, where they are readily mistaken for Mycobacterium tuberculosis complex. Molecular identification remains unavailable in most Indian diagnostic laboratories, so phenotypic characterisation continues to determine what is reported to clinicians. How well individual phenotypic markers discriminate between species has rarely been quantified.
Methods
In this observational, single-centre study, NTM isolates recovered from specimens submitted for mycobacterial culture between August 2023 and December 2025 were characterised. After decontamination, eautomated liquid culture and Ziehl–Neelsen staining, M. tuberculosis complex was excluded and every isolate underwent Runyon classification (rapid growth ≤7 days versus slow growth >7 days; pigment production in light and in darkness) followed by a three-test biochemical panel comprising semi-quantitative catalase at 68 °C, Tween 80 hydrolysis and iron uptake. Proportions are reported with Wilson 95% confidence intervals (CI). Sensitivity, specificity, predictive values and accuracy of each marker were computed against the final composite species assignment, together with cumulative species-level resolution and concordance with reference phenotypes.