Abstract
A new mobile insertion sequence designated IS1110 was detected in the strain LR541 of Mycobacterium avium due to an observed increase of the size of the plasmid pLR20. Genomic libraries of M. avium containing the original plasmid pLR20 and the modified plasmid pLR20' were constructed using the phage gammagt10 as the vector. In order to characterize the insertion sequence as well as the region of inserted DNA, the sequence of the relevant clones was determined. IS1110 is a 1457 bp element lacking terminal inverted repeats and it is related to other insertion sequences such as IS900 (M.paratuberculosis), IS901, IS902 (M.avium) and IS116 (Streptomyces clavuligerus). Several copies of IS1110 are present in the strain LR541. Individual colonies derived from the same plate show significant differences in the banding pattern obtained by hybridization techniques (Southern blot) using a partial fragment of IS1110 as probe generated by PCR technique (Polymerase Chain Reaction) which implies an unusually high degree of mobility. Initially, analysis of clinical, veterinary and environmental isolates of M.avium from different sources showed that the sequences hybridizing to IS1110 were present in only a small number of M.avium strains. However, prolonged exposure of Southern blots disclosed the presence of another insertion sequence partly related to IS1110. Furthermore, the banding patterns obtained exhibited extensive polymorphism, even between strains that had identical RFLP patterns with the pMB22 probe. These results, indicating the potential usefulness of IS1110 as an epidemiological tool led to the investigation of the occurrence and distribution of IS1110 in a larger number of M.avium strains and establishment of the extent of the polymorphism seen with IS1110 by RFLP analysis. Using a full length IS1110 probe, an important number of M.avium strains including those obtained from AIDS and non-AIDS patients hybridized to IS1110 and exhibited an extensive polymorphism. Most banding patterns were unique and seven small groups of identical strains were identified. One of these types was found to be particularly prevalent in non-AIDS subjects, and was associated with colonisation rather than dissemination or invasion. These results showed that IS1110 can be an useful tool for identification of cases of hospital cross-infection. Besides, stability of the banding patterns obtained was confirmed by repeated subculture of M.avium strains which is essential for the validity and usefulness of IS1110 as an epidemiological tool.