Isolation nontuberculous mycobacteria and histopathological changes in lymph nodes collected at the abattoir in cattle reactive-positive to tuberculin dermal test

Abstract Background: The Mycobacterium tuberculosis complex causes a variety of diseases; in bovine, the common pathogen is M. bovis which is considered zoonotic. A separate group of mycobacteria, much less known, is "non-tuberculous mycobacteria (NTM) which are also infectious for animals and humans. The Mexican Official Norm (NOM-ZOO-031-1995) regulates M. bovis in cattle, but not NTM species, even though this last type of microorganisms has a confounding effect for the diagnosis of bovine tuberculosis. The objective of the study was to isolate and identify the NTM of bovine lymph nodes condemned in the slaughterhouse, to characterize the histological lesions in these tissues and to correlate bacteriological and postmortem findings with the antemortem skin test of the tuberculin. Results: Mycobacteria were isolated from 54/528 (10.2%) of the lymph nodes; 29/54 (53.7%) of these isolates were identified as M. bovis and 25/54 (46.2%) as NTM; 3 bacteriological cultures were discarded due to contamination with fungi and in one case it was not possible to identify the species. Granulomatous and pyogranulomatous inflammation were observed in 6/21 (28.6%) and 7/21 (33.3%) of the NTM-positive lymph nodes, respectively. Necrosis and mineralization were only found in 6/21(28.6%) of the lymph nodes. The species of NTM associated with granulomatous lymphadenitis were M. scrofulaceum, M. triviale, M. terrae and M. szulgai, while those causing pyogranulomatous lesions were M. szulgai, M. kansasii, M. phlei, and M. scrofulaceum. Conclusions: Considering the increase of mycobacterial infections in humans worldwide, the idetification of NTM that inducing Tuberculosis-like lesions in abattoir inspection is the first step to investigate the livestock-human-wildlife-environment interactions with especially focus on transmission dynamics.