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The occurrence of two markers, a newly identified 40-kDa protein (p40) and the insertion sequence IS901-IS902, in strains of Mycobacterium avium subspp. was evaluated. Analysis of 184 type and field strains of the M. avium complex from human, animal, and environmental sources by PCR specific to IS901 and by a monoclonal antibody specific to p40 demonstrated the presence of the two molecular markers in all of the M. avium subsp. silvaticum strains examined and also in a number of M. avium subsp. avium strains (the latter isolated mainly from pigs). The appearance of the two markers was completely concurrent in all strains. Further, the marker-positive M. avium subsp. avium strains were mainly serotype 2, whereas M. avium complex strains of serotypes 4, 6, 8, 9, and 10 were marker negative. The M. avium subsp. avium type strain ATCC 25291 and approximately 50% of the M. avium subsp. avium field strains isolated from animals contained the markers, while only one strain of human origin was found to be marker positive. Therefore, IS901 and p40 appear to have substantial potential to differentiate among isolates of the M. avium complex. This observation raises new issues regarding classification of strains, since the presence of the markers was found to be inconsistent with the present taxonomic grouping of M. avium subspp.

A putative serine protease expressed in vivo by Mycobacterium avium subsp. paratuberculosis was isolated from a lambda g t l l genomic expression library by screening with serum from a naturally infected sheep. The gene was contained in two overlapping clones, which were shown by antibody elution to encode a protein of 34 kDa in M. a. paratuberculosis. The clones were sequenced and database searches detected a motif identical to the active serine site in trypsin, and 30% homology to the putative serine proteases (HtrA proteins) of Escherichia coli, Salmonella typhimurium, Brucella abortus and Rochalimaea henselae.