Addition of gamma-irradiated <i>Mtb</i> strains produces low level A549 cell LR aggregation.

<p>Gamma-irradiated CDC1551, HN878 and H37Rv bacilli were added to monolayers at an inoculum of 100 bacilli per host cell. The cells were then processed for confocal microscopy and LR aggregation defined by CT-B staining and quantified as described. Controls without bacilli produced LR aggregation at 6 and 24 hr post-treatment comparable to controls for other previous experiments. At 6 hr post-treatment a significant increase in LR aggregation was observed with strains H37Rv and HN878 compared to controls (*p-value <0.001). LR aggregation with all three strains at 24 hr post-treatment was significantly increased compared to controls (**p-value <0.001). Experiments were performed in triplicate and repeated three times. A total of 15 fields were imaged per coverslip, incorporating approximately 30–50 host cells per field. Data presented are the average of three experiments. Images were captured at 63x magnification.