I have colistin sulphate salt but it appears to be light yellow crystals. Ideally it should be off-white powder, so, can't figure out why is it not in powdered form. Is it possible that it has absorbed some water from air and changed to these crystals type stuff? and would the water absorption effect the activity of antibiotic as well. I want to do susceptibility testing with it. Would it be fine to proceed with it?