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EVIDENCE FOR THE MACROPHAGE INDUCING GENE IN MYCOBACTERIUM INTRACELLULARE
Citation:
PFALLER, S. L. EVIDENCE FOR THE MACROPHAGE INDUCING GENE IN MYCOBACTERIUM INTRACELLULARE. Presented at Microbes in a Changing World, Joint Meeting of the 3 Divisions of the International Union of Microbiological Societies, San Francisco, CA, July 23 - 28, 2005.
Impact/Purpose:
1)Develop an improved method(s) for isolating and/or detecting nontuberculous mycobacteria from potable water. 2)Determine the best DNA fingerprinting method to use to determine genetic relatedness with clinical and environmental isolates.
Description:
Background: The Mycobacterium avium Complex (MAC) includes the species M. avium (MA), M. intracellulare (MI), and possibly others. Organisms belonging to the MAC are phylogenetically closely related, opportunistic pathogens. The macrophage inducing gene (mig) is the only well-described virulence factor identified in MAC. The gene codes for a secreted protein putatively involved in the metabolism of fatty acids, and is induced when cells are phagocytized by human macrophages. A previous analysis of MAC strains for the presence of mig found the gene exclusively in MA and not in MI. The goal of this study was to develop mig PCR as a tool to rapidly distinguish between strains of MA and MI in the laboratory.
Methods: MAC isolates were obtained from Olive-View UCLA Medical Center in Sylmar, California. The collection contained 18 MA and 58 MI isolates obtained from patients and drinking water. A 372 bp fragment of mig was amplified using primers specific for a coding region of the gene. Products were verified by sequencing. Sequences were aligned with mig sequences obtained from reference strains and GenBank and analyzed using phylogenetic methods.
Results: mig was detected in 94% (17/18) of MA strains and 95% (42/44) of MI strains. Sequencing and phylogenetic analysis of mig revealed distinct species differences.
Conclusions: Previous studies with MAC isolates obtained from across the United States found mig present in MA and absent in MI. In contrast, mig PCR was unable to discriminate between MAC species in this study. Interestingly, the strains in our collection were isolated from a relatively small geographic region (Los Angeles, California). The divergence between MA and MI mig sequences suggests the gene was derived from a common ancestor and was not acquired by MI through horizontal gene transfer. It has been demonstrated that mig is associated with the virulence of MA, however it remains to be seen if mig is expressed or involved with the virulence of MI.