Typing Mycobacterium bovis isolates from Texas and Mexico using molecular markers

Abstract

With the rise of bovine tuberculosis in Texas, strain typing of Mycobacterium bovis is necessary to characterize potential sources of exposure and the mode of transmission. Importation of infected cattle from Mexico, immigration of potential infected farm workers, increased deer farming and transmission between herds are some of the suspected causes of the disease. This study is performed to determine the value of molecular markers in typing M. bovis isolates originating from Texas and Mexico. Eighty-eight isolates originating from herds in different geographic regions of Texas and Mexico were analyzed using molecular probes IS6110, DR and PGRS. Eighteen different fingerprint types were generated using the IS6110 probe. But the majority (82%) 71 of 87 isolates contained a single IS6110 copy distributed on one of the four different restriction fragments. In an unusual manner, the remaining isolates (18@o) contained multiple IS6110 copies in 12 different patterns. DR fingerprints were used to further differentiate these isolates. For example, the above isolates (71) were differentiated into 18 different RFLP types when used in combination with DR probe. On the whole 95 M. bovis isolates exhibited twenty-seven different DR types. By combining the patterns generated by IS6110 and DR probes it was possible to separate the isolates into 32 distinct RFLP types. Isolates exhibiting identical RFLP types were found in animals within the same herd as well as in animals in geographically distant herds. Fingerprint patterns generated using PGRS probe were too crowded to interpret the differences among the isolates. Image analysis was performed using BioImage Whole Band Analyzer program and a database representing all RFLP types was established. Dendrograms based on relatedness of IS6110 fingerprints demonstrate that M. bovis isolates from Texas are more diverse than those from Mexico. Dendrograms based on the 'DR'fingerprints shows M. bovis isolates (identical IS6110 type) from Texas and Mexico are genetically closely related. The databank of different RFLP types will provide an insight on the number of different strains prevalent in this region and improve epidemiological tracking during outbreaks.