Enterobacter aerogenes is a facultative anaerobe. It is found in the human gastrointestinal tract but does not generally cause disease in healthy individuals. Enterobacter aerogenes is a bacillus which looks as a straight rod under a microscope. As a facultative anaerobe which means that it prefers environments with little or no oxygen, such as feces, sewage plants, and soil but it can also survive and even grow where oxygen is abundant. E. aerogenes ferments both glucose and lactose as a carbon source. Since it produces hydrogen gas, it may be of commercial interest. At present, however, there is a greater concern that it is resistant to many antibiotics. Because of this resistance, it is frequently found in hospitals, where it infects weakened patients together with other pathogens.