microbiology made simple was a popular choice at my school.... you might as well try to have as much fun if you're studying something boring like micro
First Aid is the gold standard for step 1, for step 2 CK, there are several choices including First Aid, Crush Step 2, Step up to Step 2 which each have their own pluses/minuses but for both tests, you need a solid Qbank i.e. UWorld
the Best one is Principles and practice of infectious disease, but it's way too long. Use it as a reference. The best one for boards and class is medical microbiology made ridiculously simple. Unless your school loves to teach useless stuff like agars, lab tests, and microbiologist's things you'll suffice with MMMRS.