A 12 center dot 7 kb fragment of the Mycobacterium tuberculosis genome is not present in Mycobacterium bovis

Southern blotting, sequence analysis and PCR experiments showed that Mycoba cterium bovis and Mycobacterium bovis BCG lack a 12.7 kb fragment present i n the genome of Mycobacterium tuberculosis. This region is 337 bp downstrea m of the RD2 region, which was previously described as being absent from so me M. bovis BCG strains. The 12.7 kb fragment should be useful as a target for a PCR test to differentiate M. tuberculosis and M. bovis. An analysis o f the 12.7 kb region suggests that it represents a deletion in M. bovis rat her than an insertion in M. tuberculosis. The deletion removes most of the mce-3 operon, one of four highly related operons which may be involved in c ell entry, and therefore it may contribute to differences in virulence or h ost range in the two species.