Non-tuberculous mycobacteria in cattle: Distribution, antimicrobial resistance and zoonotic implications in Tamil Nadu, India.

Abstract

Non-tuberculous mycobacteria (NTM), once regarded as environmental pathogen, are now recognized as opportunistic pathogens capable of infecting humans and animals, interfering with the diagnosis of bovine tuberculosis and posing significant therapeutic challenges in humans. This study aimed to determine the prevalence of NTM in bovines and to characterize circulating species using genetic and protein mass profiling methods. A cross-sectional study was conducted with a total of 409 bovine samples, including nasal swabs (154), faecal samples (157), milk (50) and lung tissues (48) collected from farms and slaughterhouses across Tamil Nadu. Samples were processed using standard bacteriological protocols and acid-fast isolates were confirmed by PCR targeting the hsp65 gene, followed by partial gene sequencing and MALDI-TOF MS for species identification. The overall prevalence of NTM was 2.2% (9/409). Identified species included Mycobacterium kansasii, Mycobacterium asiaticum, Mycobacterium kyorinense, Mycolicibacterium fortuitum and Mycolicibacterium smegmatis. All species identified in this study, except M. kansasii, are reported for the first time from animals in India, and M. kyorinense is reported for the first time from animals globally. Sequencing and MALDI-TOF MS showed good concordance for species identification. Antimicrobial susceptibility testing was performed using the broth microdilution method against selected first and second line antimycobacterial drugs, revealing diverse resistance patterns, with several isolates exhibiting resistance to first-line anti-tuberculosis drugs. This study provides novel data on NTM prevalence and species diversity in bovines, highlighting their zoonotic potential and emphasizing the need for improved surveillance, accurate diagnostics and antimicrobial stewardship in livestock-public health interfaces.