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Int J Tuberc Lung Dis. 2005 Aug;9(8):907-14.

Morphological variability and cell-wall deficiency in Mycobacterium tuberculosis 'heteroresistant' strains.

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Institute of Microbiology, Bulgarian Academy of Sciences, Sofia, Bulgaria.



Sofia State Hospital for Tuberculosis Treatment, Bulgaria.


To investigate the morphology of two 'heteroresistant' clinical isolates and one non-heteroresistant isolate, all isolated from newly diagnosed tuberculosis (TB) patients, as well as the reference strain H37Rv. Heteroresistant isolates contained clonally-related sensitive and drug-resistant organisms which could subsequently be separated using drug-containing primary cultures and had been isolated from patients originally diagnosed with susceptible TB by the 1% proportion method. Mycobacterial cultures were evaluated by transmission electron microscopy after 25 days of cultivation in Dubos broth.


In contrast to H37Rv and the non-heteroresistant isolate, the bacterial populations in both heteroresistant isolates demonstrated distinct pleomorphic variability and coexistence of both classical and cell-wall deficient forms. Electron micrographs of mutants resistant to streptomycin and isoniazid showed predominance of atypical granular L-forms, which formed L-type colonies on Dubos agar.


The L-form transformation processes, observed both in clinical heteroresistant isolates containing mixed populations of Mycobacterium tuberculosis organisms with different resistance gene genotypes and in the isolated resistant (mutant) clones, indicate a possible link between resistance and cell-wall deficient L-phase states and suggest one of the possible mechanisms by which resistant mutants are able to survive in vivo.

[Indexed for MEDLINE]

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