Identification of non-tuberculous mycobacteria in slaughtered cattle from Chennai, India

Abstract

Non-tuberculous mycobacteria (NTM) are emerging pathogens in human and veterinary medicine, with a globally increasing incidence. In India, sporadic studies have identified an upward trend in NTM infections, but accurate prevalence estimates are lacking due to the absence of nationwide surveillance. Non-tuberculous mycobacteria have been reported in clinically healthy cattle and wildlife globally, complicating tuberculosis (TB) diagnostics and surveillance. This study aimed to characterize NTM species isolated from tissue samples of slaughtered cattle in Chennai using culture and targeted hsp65 gene sequencing. A total of 118 presumed NTM samples from 115 animals were processed, and 49 isolates were confirmed as NTMs by PCR. Sequencing identified 18 different species, with Mycobacterium intracellulare (9/49) being the most frequent, followed by Mycobacterium sp. strain 79_MI18_10584 (6/49) and Mycobacterium elephantis (6/49). Several identified species, including M. intracellulare, M. fortuitum (5/49), M. kansasii (4/49), and M. avium, have caused infections in humans as well. NTMs in cattle lymph nodes without visible lesions suggest their asymptomatic persistence, albeit there being a possibility of transient colonization. Non-tuberculous mycobacteria complicate bovine tuberculosis (bTB) diagnostics by inducing cross-reactive immune responses and forming granulomatous lesions resembling those caused by Mycobacterium tuberculosis complex (MTBC). This study highlights the presence and diversity of NTMs in Indian cattle and emphasizes the need for better surveillance, improved molecular characterization, and better understanding of their epidemiological and immunological roles in both veterinary and public health contexts.