Cytotoxicity of alkaline-tolerant dairy-associated Bacillus spp.

The cytotoxicity of five Bacillus spp. isolated from alkaline cleaning solu tions in South African dairies was evaluated against McCoy mouse cells usin g a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)-base d assay, confocal scanning laser microscopy and scanning electron microscop y. According to the MTT-based assay, two of the Bacillus isolates (Bacillus licheniformis 5 and B. pumilus 122) were cytotoxic to McCoy cells and the cytotoxic components were heat labile. Confocal scanning laser microscopy c ombined with fluorescent staining using propidium iodide and fluorescein di acetate indicated that cytotoxic effects occurred within 3 h, appeared to b e membrane active and resulted in cell necrosis. Scanning electron microsco py showed that McCoy cells exposed to the cytotoxic components exhibited mo rphological damage.