DNA-FINGERPRINTING WITH 2 PROBES DECREASES CLUSTERING OF MYCOBACTERIUM-TUBERCULOSIS

DNA fingerprinting of Mycobacterium tuberculosis is used to study the epidemiology of tuberculosis, but the specificity of the widely used I S6110 technique has not been validated. Isolates from Denver, Colorado from December 1988 through lune 1994 were fingerprinted with the IS61 10 technique. Available records were reviewed for patients whose isola tes were within IS6110-defined clusters, and these isolates were finge rprinted with an independent technique (pTBN12). Of 189 isolates, 86 ( 46%) were in IS6110-defined clusters. Clustering was inversely related to the number of copies of IS6110, ranging from 12 of 12 (100%) to 37 of 48 (77%) and 37 of 129 (29%) for isolates having one, two to five, and more than five copies (p < 0.001). Of the 86 isolates clustered w ith the IS6110 technique, 35 (41%) had unique pTBN12 fingerprints. Dis cordant results with the two fingerprinting techniques were more commo n among isolates having five or fewer copies of IS6110. Epidemiologic links were identified among four of 35 (11%) patients whose isolates h ad discordant fingerprinting results, as compared with 40 of 51 (78%) of those whose isolates matched by both IS6110 and pTBN12. DNA fingerp rinting with the IS6110 technique was not a specific marker of DNA clo nality, particularly among isolates having fewer than five copies of I S6110. The use of a supplemental DNA fingerprinting technique decrease d clustering and improved the correlation between the transmission lin ks predicted by molecular techniques and epidemiologic investigation.