Michael refers to Ahmed's infection as viral, but at his home, Sam says Nate is working with highly infectious bacteria, not viruses.
Jesse drinks Ahmad Damour's glass of whiskey then says he will get the next round but in the next shot the glass is full again before he has ordered it.
Gram staining is a method of discriminating between two basic types of bacteria, but the result isn't macroscopic - the stained bacteria must be viewed under a microscope.