I have a cat that has pus on 2 of her feet (one in back and one in front) around the pads.?

I have a cat that has pus on 2 of her feet (one in back and one in front) around the pads. I have tried changing the cat litter and putting triple antibiotic ointment on them and have cleaned the very well with warm water. I am at a loss for what to do about this. Does anyone know what this could be?