Mycobacteria in pond waters as a source of non-specific reactions to bovine tuberculin in New Zealand.

When 71 samples were collected from ponds throughout New Zealand, 35 (49.3%) were found to contain mycobacteria. The majority of these strains (62.9%) belonged to a homogeneous group (tentative designation H-Group, which differed from any known mycobacterial species. Mycobacteria of this H-group had also been found in sphagnum vegetation growing in the immediate vicinity of many of the ponds. H-Group mycobacteria induce sensitization in guinea pigs against bovine tuberculin. The PPD sensitin prepared from these mycobacteria gave rise to larger reactions in guinea pigs than did bovine tuberculin when used in the same concentrations (500 and 50 TU). The possible sensitization of cattle to bovine tuberculin via drinking water containing H-Group mycobacteria, is discussed. The larger size of the delayed hypersensitivity reactions in guinea pigs using the same concentrations of bovine and homologous tuberculin, suggests that comparative intradermal testing might enable this non-specific reaction to be distinguished from the specific reaction developed during bovine tuberculosis infection in cattle.