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The distribution of 20 variable regions resulting from insertion-deletion events in the genomes of the tubercle bacilli has been evaluated in a total of 100 strains of Mycobacterium tuberculosis, Mycobacterium africanum, Mycobacterium canettii, Mycobacterium microti, and Mycobacterium bovis. This approach showed that the majority of these polymorphisms did not occur independently in the different strains of the M. tuberculosis complex but, rather, resulted from ancient, irreversible genetic events in common progenitor strains. Based on the presence or absence of an M. tuberculosis specific deletion (TbD1), M. tuberculosis strains can be divided into ancestral and 'modern' strains, the latter comprising representatives of major epidemics like the Beijing, Haarlem, and African M. tuberculosis clusters. Furthermore, successive loss of DNA, reflected by region of difference 9 and other subsequent deletions, was identified for an evolutionary lineage represented by M. africanum, M. microti, and M. bovis that diverged from the progenitor of the present M. tuberculosis strains before TbD1 occurred. These findings contradict the often-presented hypothesis that M. tuberculosis, the etiological agent of human tuberculosis evolved from M. bovis, the agent of bovine disease. M. canettii and ancestral M. tuberculosis strains lack none of these deleted regions, and, therefore, seem to be direct descendants of tubercle bacilli that existed before the M. africanum [right arrow] M. bovis lineage separated from the M. tuberculosis lineage. This observation suggests that the common ancestor of the tubercle bacilli resembled M. tuberculosis or M. canettii and could well have been a human pathogen already. evolution | diagnostic | identification

The entire genome sequence of the Mycobacterium tuberculosis, H37Rv strain has been determined and analyzed. A systematic sequence analysis of selected large-insert clones and random small-insert clones was used to obtain the genome sequence, resulting in the sequence of 4,411,529 base pairs. 50 genes coding for functional RNA molecules were discovered, as well as 16 copies of the insertion sequence IS6110 and six of the IS1081 sequence. It shows that the tubercle bacillus is able to synthesize all amino acids, enzyme co-factors and vitamins, differing from other bacteria in that it devotes much of its coding capacity to enzyme production involved in lipogenesis and lipolysis.

A prevalence study was conducted between Mar. and Oct. 1994 to identify the sources of serotype O157:H7 isolates of Escherichia coli in Wisconsin dairy herds. A total of 302 environmental samples were examined, including two drinking water samples. Results suggest that there are several clonal types of serotype O157:H7 isolates in Wisconsin. The data also indicate that there is more than one source of this pathogen in Wisconsin dairy farms.