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Genetic relationships, subspecific differentiation and molecular epidemiology of mycobacteria

Feizabadi, Mohammad Mehdi (1996) Genetic relationships, subspecific differentiation and molecular epidemiology of mycobacteria. PhD thesis, Murdoch University.

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In this study genetic relationships amongst and between isolates belonging to the Mycobacterium avium complex (MAC) and the M. tuberculosis complex, as well as other mycobacteria which are genetically and phenotypically related to the MAC including M. paratuberculosis, M. scrofulaceum and “X” Mycobacteria, were examined. For this purpose multilocus enzyme electrophoresis (MEE) and pulsed field gel electrophoresis (PFGE) were standardised for mycobacteria, and then used to compare isolates of these bacteria.

Isolates of the M. tuberculosis complex and isolates of M. paratuberculosis each were closely related, and each are likely to represent a single species. Isolates of M. avium and M. intracellulare were different from each other and from the other mycobacterial species examined. While isolates of M. avium were clustered in several sub-groups by MEE, most of the isolates of M. intracellulare were differentiated and represented a heterogeneous group. Similarly M. scrofulaceum and “X” mycobacteria were found to be heterogeneous and it is likely that each of these groups contains several species.

Most isolates of M. avium cultured from chickens in Australia belonged to a few closely related electrophoretic types (ET). As isolates from pigs from Tasmania also were located in some of these ETs, it is likely that transmission of infection between the two species has occurred. Conversely in other states of Australia no evidence of this cross-species transmission was evident. All isolates of M. avium cultured from animals were found to have different DNA banding patterns from isolates cultured from humans. Patients with Acquired Immunodeficiency Syndrome (AIDS) and those without AIDS were found to be infected with genetically diverse isolates of M. avium suggesting that infection occurred from the environment.

Isolates of M. bovis were homogeneous, and as only a few specific strains were detected on numerous Western Australian farms it is likely that spread of the infection was primarily due to movement of infected stock. In contrast, in Canada outbreaks of bovine and cervine tuberculosis were found to have occurred independently of each other.

Isolates of M. paratuberculosis were divided into nine PFGE patterns, and movement of infected livestock appeared to be the major factor influencing the spread of this disease in Australia. Evidence of cross-species transmission between sheep and goats and between cattle and alpacas was detected.

Australian residents who were born overseas were found to be infected with a more diverse group of M. tuberculosis isolates than were Australian born patients. Infection in Australia is most likely to be as a result of reactivation of a previous infection. Hence it is predicted that infection with M. tuberculosis in Australians in the future will increasingly be with strains that are now common in young migrants.

The population genetics of mycobacteria differed widely for each species, despite the similarity of clinical signs induced by infection. It is concluded that MEE and PFGE are useful tools for investigating genetic relationships between mycobacteria, and for studying their epidemiology. The speciation of some organisms in this genus needs to be reconsidered.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary Studies
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Robertson, Ian and Hampson, David
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