In constant battle with antibiotics?!?
You might mean how the arms race between humans and their parasites ( including bacteria and viruses ) is an ongoing evolutionary struggle where when humans develops an immunity to some parasite the parasite evolves around that immunity.
Or you might mean how antibiotics only kill some parasites ( mainly bacterial in nature ) and those that survive give rise to the next generation that is resistant to that antibiotic so that we are running out of effective defenses against such onslaughts. Another product of evolutionary processes.