Seventy-nine Mycobacterium bovis isolates recovered from Mexican and Texas cattle were categorized into 16 and 25 distinct types on the basis of IS6110 and direct-repeat fingerprint patterns, respectively. By using a combination of both fingerprint patterns, 30 distinct restriction fragment length polymorphism types were defined. Fifty-eight of 79 isolates (73%) were distributed among nine clusters. Clustered isolates were identified within herds, as well as in geographically disperse herds in Texas and Mexico. This observation is consistent with active transmission within herds and among herds, presumably as a result of active or historical cattle movements. The majority of bovine isolates (64 of 79) exhibited a single copy of IS6110. Interestingly, in contrast to previous studies, a high percentage of bovine isolates (15 of 79) exhibited multiple IS6110 copies (two to five) distributed among 11 different restriction fragment length polymorphism types. It is speculated that transmission from noncattle sources may be responsible. Continued fingerprinting of isolates originating from nonbovine sources and herd surveys is expected to provide useful information regarding the epidemiology of tuberculosis in this region.
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