Figure 4.

Transmission electron microscopy (TEM) of M. bovis BCG lux infected haemocytes (dose 1 × 10⁷ CFU per larva) in vivo from G. mellonella over a time-course from 24 h to 336 h. Haemolymph was extracted from the haemocoel of G. mellonella (n = 10) at 24 h intervals post-infection by puncturing the larvae in the last left pro-leg using a sterile needle. Haemolymph was pooled, processed and analyzed using a Tecnai bioTWIN transmission electron microscope. M. bovis BCG lux inoculum alone served as a control (A). Further figures (B-H) show the haemolymph contains haemocytes (arrow, B) and the time-course study showed the ultrastructure of initial internalization of BCG lux into cells at 24 h (arrowhead, B). From 24 h to 366 h, aggregation of bacilli, typical to that found in granulomas was evident. TEM confirmed that over the time-course the bacteria invade or are phagocytosed by haemocytes and multiply within to form aggregations of bacilli, typical of those found in granulomas. There is also an increase in lipid material within M. bovis BCG lux during the time-course (arrow, D). Scale bar represents 500 nm (A-E, G) and 2 µm (F, H).