Bacteria of the <i>Mycobacterium avium, M. intracellulare, and M. scrofulaceum</i> group (MAIS) are opportunistic human pathogens and widespread in the environment. The first objective of this study was to demonstrate that plasmids from clinical isolates are closely related to plasmids from environmental MAIS isolates. A 12.9 kb plasmid, pVT2, from a clinical <i>M. avium isolate</i>, MDl, was cloned and used a a DNA probe to examine the relationship of MAIS plasmids. The pVT2 probe hybridized with plasmids isolated from MAIS strains from the environment, from patients without AIDS with pulmonary infections, and from AIDS patients with disseminated MAIS infections. Similar results were seen with a second probe derived from pLR 7, a 15.3 kb plasmid from clinical <i>M. intracellulare</i> strain LR 113. The similarity of plasmids from environmental and clinical isolates supports the hypothesis that the environment is a source of MAIS infection in humans. / Ph. D.

Mycobacterium avium and Mycobacterium intracellulare, (M. avium complex, MAC) are human pathogens causing disease in individuals with acquired immunodeficiency syndrome (AIDS) or with thoracic abnormalities. MAC bacteria are difficult to kill because of the resistance of the pathogens to chemotherapeutic agents. One factor affecting treatment of MAC disease is the presence of interconvertible colonial variants. Transparent (T) variants have greater resistance to antibiotics and higher pathogenicity; opaque (O) variants are more susceptible to antibiotics and less pathogenic. The overall goal of this study was to investigate the mechanism for colonial variation. Based on an observation that T variants of M. intracellulare strain Va14 contained a plasmid which was 6 kb smaller than the 68 kb plasmid in O variants, it had been suggested that a transposable element might be responsible for colonial variation. The first objective was to clone the unique DNA fragment present in the 68 kb plasmid but absent from the 62 kb plasmid. The second and third objectives were to determine if the unique fragment contained a transposable element and to analyze the role of that element in the mechanism of colonial variation in M. intracellulare strain Va14. The fourth objective was to determine the distribution of IS1141 in MAC isolates. Fragments containing copies of the putative element were sequenced and a region 1596 basepairs in length with 23 basepair imperfect inverted repeats was designated as insertion sequence IS1141. IS1141 is the first insertion sequence identified in M. intracellulare. Data base searches using open reading frames (ORF) of IS1141, identified ORFb as significantly similar to the transposases of the IS3 family. The presence or absence of IS1141 in strain Va14 plasmids appeared unrelated to colonial variation, but IS1141 was present in another plasmid and the chromosome of the Va14 variants. Hybridization studies with IS1141 identified three chromosomal copies in O variants and two chromosomal copies in T variants. Va14 T variants each had a common IS1141 restriction fragment length polymorphism (RFLP) pattern which was different than the single RFLP pattern found in opaque variants. Based on these differences, it appears that IS1141 may integrate into the gene(s) responsible for the T phenotype preventing their expression. A survey of 64 James River basin non-AIDS, clinical and James River environmental MAC isolates identified 4 of 24 (17%) M. intracellulare isolates as containing IS1141. IS1141 has not been detected in any clinical or environmental M. avium or Mycobacterium species X isolates and may be limited to M. intracellulare. / Ph. D.

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