Propidium iodide can stain dead or fixed bacteria (obviously the DNA). However, for "extracellular" DNA, it's likely to be unwound or even broken up. In its uncoiled form, DNA density is too low, and unless you have super-high resolution microscopes, it's going to be very challenging.

You can consider designing a biochemical experiment instead, using centrifugation to compact things. Sometimes if not often imaging is not the best approach.

Good luck.