Positive (with Isoniazid) and negative controls (without drugs) were included. The plate was incubated in the same conditions for 48 h. Subsequently, the sulforhodamine B (SRB) (Sigma Chemical Co.) colorimetric assay was carried out. The cells were fixed by adding 10% trichloroacetic acid (TCA) and incubating for 1 h at 4 8C. The plates were washed with distilled water, air-dried, and stained with SRB solution (0.4%, w/v in 1% acetic acid) at 4 8C for 30 min. Cells were washed four times with 1% acetic acid. The bound SRB stain was solubilized with 150 mL of 10 mM Tris buffer (Sigma).