RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISM TYPING OF CLINICAL ISOLATES OF MYCOBACTERIUM-TUBERCULOSIS FROM PATIENTS WITH PULMONARY TUBERCULOSIS IN MADRAS, INDIA, BY USE OF DIRECT-REPEAT PROBE

Large numbers of Mycobacterium tuberculosis isolates that were obtaine d from patients' sputa on diagnosis and during follow-up after short-c ourse chemotherapy in Madras, India, have either no copy or only a sin gle copy of IS6110. This poses a limitation for DNA fingerprinting wit h an IS6110-based probe to determine the frequency of exogenous reinfe ction versus that of endogenous reactivation. In the present study, we overcame this limitation by using an alternate probe, the direct-repe at element. Comparison of pre- and posttreatment isolates by direct-re peat restriction fragment length polymorphism analysis indicated a hig h degree of endogenous reactivation among patients who have relapses a fter the successful completion of chemotherapy.