Use of multilocus enzyme electrophoresis to examine genetic relationships amongst isolates of Mycobacterium intracellulare and related species

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Abstract
As part of a larger study investigating diversity and distribution ofMycobacteriumspp. in Australia, multilocus enzyme electrophoresis was used to assess genetic relationships at 17 enzyme loci amongst a collection of reference strains and isolates initially identified on biochemical and other grounds asM. intracellulare(70), ‘X’ mycobacteria (10),M. scrofulaceum(7),M. avium(8) andM. aviumsubsp.paratuberculosis(2). Two of the isolates initially identified asM. intracellularewere shown to be quite distinct from the others. Both gave negative results in a species-specific DNA probe test, whilst one was positive by PCR. These results emphasize the uncertainties involved in identifying members of this group. The otherM. intracellulareisolates formed a cohesive but diverse group, being divided into 48 electrophoretic types (ETs), with a mean genetic diversity of 0∙38. Forty-three of these ETs contained only single isolates. There was no clear relationship between the serovar and ET designation. The index of association calculated forM. intracellularewas significantly different from zero, suggesting that it is a clonal species. PFGE was also applied to selected isolates from the ETs containing multiple isolates, and some of these could be differentiated further. The strains ofM. scrofulaceumand ‘X’ mycobacteria were distinct fromM. intracellulare, but themselves were highly heterogeneous, with mean genetic diversities of 0∙66 and 0∙65, respectively. Each of these groups may represent more than one species.M. aviumstrains were distinct from the twoM. aviumsubsp.paratuberculosisstrains, as well as from the other mycobacteria studied.

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