REPEATED DNA-SEQUENCES IN MYCOBACTERIA

In tuberculosis, it is often important to establish the source of infe ction and to determine whether disease is due to a new strain of Mycob acterium tuberculosis or to relapse. To cope with the resurgence of tu berculosis and atypical mycobacterioses in AIDS patients, on the one h and, and to overcome the limitations of classical bacteriological proc edures on the other, the development of rapid, sensitive, and reliable diagnostic and epidemiologic tools is highly desirable. Molecular typ ing methods are often based on repeated genes such as those for rRNA. Ribotyping is of limited use with pathogenic mycobacteria, as the slow -growers possess a single rRNA operon, while the fast-growers have two . This problem has been overcome by the discovery and study of repeate d DNA elements in mycobacterial genomes, as these provide an alternati ve pathway for diagnostic and epidemiological investigations.