"the polymer attaches to the bacteria's membrane and then facilitates destabilization of the membrane" vs "act by inhibiting the synthesis of the peptidoglycan layer of bacterial cell walls".
And the resistance isn't to getting your head blown off. That's thinking too much in the box. It's more like being resistant to having a bullet shot at your head, either by somehow becoming invisible to your assailant's vision, wearing a sufficiently good helmet, or having your vital organs located somewhere else.
While I agree that it seems much harder for bacteria to overcome this new approach, it really isn't safe to say that it's not possible. We have no idea about the microbial world. We barely know a fraction of the microbes that swarm around us, we have no idea what defenses, mechanisms and quirks they have that might provide a method of resistace.
And since this is a passive process (just some polymer floating around) that somehow does not damage human cells, you can bet that there's someway to spoof that.