Necrosis and apoptosis induction by KZN <i>M. tuberculosis</i> strains <i>in vitro</i>.

<p>Erdman and H37Rv reference strains were compared to sensitive (S), multidrug-resistant (M), and extensively drug-resistant (X) KZN strains. (A) For necrosis measurement, alveolar epithelial cells (A549) were infected with the KZN strains at MOI of 10 for 96 h and the supernatant was assayed for lactate dehydrogenase (LDH). Percentage cytotoxicity was calculated by the following formula: [release of LDH from infected cells (OD490)-release of LDH from uninfected control/maximum LDH release (OD490)] X 100. Data from four independent experiments. (B) Infected A549 cells were lysed and plated to monitor bacterial survival. (C) The percentage of apoptosis of THP1 macrophages infected with the KZN strains at an MOI of 10 was determined by TUNEL staining of DNA fragmentation. Values are means with error bars indicating standard error. Statistically significant differences in necrosis relative to that of Erdman are shown: *, P<0.05; **, P<0.001.