IS6110 RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISM TYPING OF CLINICAL ISOLATES OF MYCOBACTERIUM-TUBERCULOSIS FROM PATIENTS WITH PULMONARY TUBERCULOSIS IN MADRAS, SOUTH-INDIA

Setting: Madras, India. Objective: To explore the utility of a standar dized IS6110/PvuII deoxyribonucleic acid (DNA) fingerprinting restrict ion fragment length polymorphism (RFLP) typing method for distinguishi ng between isolates of Mycobacterium tuberculosis, and to assess the p otential for distinguishing between relapse versus reinfection rates. Design: To assess RFLP heterogeneity in the population, initial isolat es, obtained from the sputum of tuberculous 98 patients on diagnosis a nd follow-up during short-course chemotherapy, were stored and compare d. To assess the frequency of disparity between the RFLP type of the i nitial isolate and one obtained after successful completion of chemoth erapy, either during relapse or as an isolated positive culture, 124 i solates comprising 62 such pairs were coded and compared both blind an d after decoding. Results: Although a wide variety of DNA band pattern s (fingerprints) was present, the isolates from 39 (40%) of the patien ts showed a single copy of IS6110. Only 15 pairs of coded initial and follow-up isolates could be identified as having the same band pattern when isolates with zero or single bands were excluded. Nevertheless, after decoding, in a retrospective analysis that included all isolates , those isolates that bacteriologically defined a patient's relapse mo re often showed RFLP type identity with the initial isolate (19 of 30 comparisons) than did isolates that were obtained as isolated positive cultures (3 of 32 comparisons) (chi(2) P < 0.001). Tests of sensitivi ty to chemotherapeutic drugs, catalase activity and resistance to thio phene-2-carboxylic acid hydrazide were of minimal value in discriminat ing between isolates. Conclusions: Despite the high frequency of singl e- and zero-band isolates in this population, the discriminatory power of RFLP typing with IS6110 is sufficiently high to be useful for clin ical and epidemiological studies.