Students often have some real problems accepting that most bacteria are not harmful. They also have trouble believing that our bodies were designed to ward off pathogens. I have included more information on this in the notes for Chapter 39. You might wish to copy and distribute to your students the Overview of Chapter Objectives flowchart found at the beginning of this Instructor's Manual Chapter. I suggest you begin this chapter with a non-quiz.
Most bacteria are harmful.
Viruses and bacteria are the same thing. We really don't use enough antibiotics to get rid of all the disease causing bacteria. Of course all four answers are false. You may be surprised at the misconceptions your students have. I also suggest you make some bacterial plates.