Creationists invented the micro/macro "argument" because they know that they cant deny examples of evolution that we have seen on a small scale in the recent past. Evolution takes place over millions of years, but by small changes in single generations. Simple concept really.
The development of Antibiotic resistant bacteria is a perfect example of naturally selected mutations. The resistance was not "built in." It has nothing to do with immunity. It's Evilution, baby.