Enterobacter includes eleven species of highly motile bacteria. The Enterobacter species is biochemically similar to Klebsiella, the key difference being that Enterobacter is ornithine positive. Although this bacterium is part of the normal flora of the human intestinal tract, several species cause opportunistic infections of the urinary tract as well as other parts of the body. E. aerogenes and E. cloacae are two such pathogens that do not cause diarrhea, but that are sometimes associated with urinary tract and respiratory tract infections.