Detection of nontuberculous mycobacteria in milk and nasal swab of cattle tested positive by tuberculin skin test, Interferon-γ release assay and MycoPac dual lateral flow assay.

The Single Intradermal Comparative Cervical Tuberculin (SICCT) and Interferon-γ release assay (IGRA) test represent a major antemortem diagnostic test for preliminary detection of bovine tuberculosis in a herd. Very few studies have focused on identifying the mycobacterial species in the milk and nasal swab of SICCT- and IGRA-positive animals. This study was carried out to identify the presence of Mycobacterium in the milk and nasal swab from SICCT- and IGRA-positive cows in a herd in West Bengal, India. Out of the study population of 250 lactating animals, 12 (4.8%) cows were positive for the SICCT and IGRA. Aseptic collection of milk and nasal swab samples and their inoculation onto the sterile Lowenstein-Jensen (L-J) medium was done. Ziehl-Neelsen staining was conducted in order to identify acid-fast bacilli and detect colonies that were consistent with mycobacteria. Conventional PCR was done to confirm the Mycobacterium genus. Several NTM species such as M. massiliense (n = 7), M. senegalense (n = 6), M. abscessus (n = 5), M. conceptionense (n = 3), M. peregrinum (n = 1) and M. terrae (n = 1) were identified by Sanger sequencing and sequence analysis of the hsp65 gene. Many of the mycobacterial species isolated in this study can cause pulmonary and extrapulmonary diseases, affecting both immunocompetent and immunocompromised individuals. So, identification of these mycobacteria in raw milk, and nasal swabs underscores the possibility of disease spread from cows, posing significant public health risk.