ASPG and infection: Using an MTT assay to quantify the metabolic activity of the tumours and microscopy to assess organoid growth qualitatively, we found that STmΔaroA infection significantly reduced the metabolic activity of tumour organoids (p < 0.001 NT vs STmΔaroA), with the appearance of darkened, blebbing organoids (indicating cell death), which was reversed by addition of exogenous asparagine or the asparaginase-deficient mutant (Fig. 8B,C).