Bacterial staining on formaline fixed spheroids

I am working with human cells spheroids model. I am infecting spheroids with bacteria and using Baclight red bacterial stain for visualising bacteria in the spheroid. I have noticed that Baclight red stains bacteria and also mammalian cells which makes it difficult to differentiate. Can anyone recommend a good dye or antibody for specifically staining bacteria (gram+ve and –ve) formaldehyde-fixed human cells spheroid?