Molecular detection of Mycobacterium bovis and Mycobacterium bovis BCG (Pasteur) in soil

PCR primers specific for the Mycobacterium tuberculosis complex were used to detect the presence of Mycobacterium bovis BCG (Pasteur) in soil microcosms and Mycobacterium bovis in environmental samples taken from a farm in Ireland with a history of bovine tuberculosis. M. bovis genes were detected in soil at 4 and 21 months after possible contamination. Gene levels were found in the range of 1 x 10(3) to 3.6 x 10(3) gene copies g of soil(-1), depending on the sampling area. Areas around badger setts had the highest levels of detectable genes and were shown to have the highest levels of gene persistence. M. bovis-specific 16S rRNA sequences were detected, providing evidence of the presence of viable cells in Irish soils. Studies of DNA turnover in soil microcosms proved that dead cells of M. bovis BCG did not persist beyond 10 days. Further microcosm experiments revealed that M. bovis BCG survival was optimal at 37 degrees C with moist soil (-20 kPa; 30% [vol/wt]). This study provides clear evidence that M. bovis can persist in the farm environment outside of its hosts and that climatic factors influence survival rates.