Abstract
The action of isoniazid on tubercle bacilli and the mechanism of the isoniazid-resistance in mycobacteria were studied with 14C-labelled isoniazid. The drug-sensitive, parent H37Rv strain of Mycobacterium tuberculosis and its mutant strain resistant to 50 mcg/ml of isoniazid were cultivated in a synthetic, liquid medium containing Tween 80 for 10 to 28 days at 37°C. The cells of tubercle bacilli were centrifuged and washed thrice with phosphate buffer. These cells were resuspended in phosphate buffer and 14C-isoniazid was added to the suspension to give the concentration of 1 to 5 mcg/ml. After the incubation at 5° or 37°C for 24 hours, the cells were washed thoroughly with saline containing Tween 80, placed on sample dishes and counted with a gas flow counter.
Results obtained were as follows, the isoniazidresistant Hs7Rv-RINH strain bound less amount of isoniazid than the sensitive H37Rv strain did; the amount of isoniazid bound by the sensitive strain reached maximum at the 6th hour of incubation, whereas isoniazid absorbed by the resistant strain did not differ in amount throughout the first 24th hours of incubation; the isoniazid-sensitive strain bound more amount of isoniazid at 37°C than at 5°C, whereas the resistant strain absorbed the same amount of isoniazid either at 37°C or at 5°C.
In the sensitive strain, cells harvested from a young culture bound more amount of isoniazid than the cells havested from an old culture, whereas in the resistant strain, no difference was observed in the amount of isoniazid absorbed the cells from an old culture and those from a young culture. These results suggested that the binding of isoniazid by the resistant strain would be due to the non specific absorption having no relation to the metabolic activity of the cells. On the other hand, the sensitive strain was observed to bind a larger amount of isoniazid taken up by the metabolic activity of the cells.
