Phagocytosis is probably the first step for mycobacteria to be virulent in host because virulent strains are more readily phagocytosed by macrophage than attenuated strains. According 13 the traditional concept, multi-drug resistant strains have been regarded as less virulent. However, this concept has been challenged, since recent studies(reported) showed that the degree of virulence and drug-resistance is not related. The purpose of this study is to evaluate whether the phagocytic activity of M. tuberculosis by peripheral blood mononuclear cells(PBMC) is different according to drug-resistance or host factor. To evaluate this, we estimated the difference of phagocytic activity of drug-resistant and drug-sensitive M. tuberculosis and also estimated the phagocytic activity of PBMC from intractable tuberculosis patients and healthy controls.

PBMC from ten intractable tuberculosis patients and twelve healthy control and three different strains of heat-killed M. tuberculosis, ie, ADS(all drug sensitive), MDR(multi-drug resistant), and ADR(all drug resistant) were used. After incubation of various strains of M. tuberculosis with PBMC, the phagocytic activity was evaluated by estimating proportion of PBMC which have phagocytosed M. tuberculosis.

Drug-resistant strains of M. tuberculosis were phagocylosed easily than drug sensitive strains(Percentage of PBMC phagocytosed M. tuberculosis in healthy control : ADS : 32.3α2.9%, ADR : 49.6α3.4%, p=0.0022, Percentage of PBMC phagocytosed M. tuberculosis in intractable tuberculosis patients : ADS : 34.9α3.6%, ADR : 50.7α4.5%), p=0.0069). However, there was no difference in phagocytic activity of PBMC from healthy control and intractable tuberculosis patients.

Drug-resistant strains of M. tuberculosis were phagocytosed easily than drug sensitive strains and host factors does not seems to influence the phagocytosis of M. tuberculosis.