Drinking regular milk will not only give kittens diarrhea, but will also cause them to slowly starve to death if their diet isn't properly supplemented [source: Kitten Rescue]. The ratio of caseins and whey in cow's milk is nowhere near sufficient to support a growing kitten [source: Fries].
One of the significant adaptions occurred in one strain of E. coli. In general, this bacteria is known for not being able to use citrate in an aerobic environment as an energy source, even though it could use citrate under anaerobic conditions because it already has the machinery to process citrate.
Escherichia coli, more commonly known as E. coli, is a group of bacteria that populate the human (and animal) gut. E. coli is usually thought of as a good bacterium; it lives in the intestines as part of the normal gut flora.. However, some strains of E. coli can cause very serious illness. These disease-causing (virulent) strains are usually classified by the action they have on the gut; these strains include enterohemorrhagic (called EHEC), enteropathogenic (called EPEC), enteroinvasive (called EIEC), and enterotoxigenic (ETEC).