CRE (carbapenem-resistant Enterobacteriaceae) bacteria are members of related bacterial genera that are commonly found almost everywhere in the world, often colonizing humans and animals (living in or on humans and animals mucosal surfaces, gastrointestinal tracts, and on some areas on the skin). However, CRE possess a unique genetic makeup that allows the bacteria to make an enzyme that protect CRE bacteria from a powerful antibiotic: carbapenem. The most notable genera that can share and even transfer this genetic trait to other members of the Enterobacteriaceae are E. coli and Klebsiella pneumoniae. Because these bacteria generate similar problems for patients (especially treatment difficulties), most investigators simply group them together and term them CRE bacteria (some researchers term those bacteria that produce the enzyme carbapenemase CP-CRE bacteria). Similar types of components are termed KPC (Klebsiella pneumoniae carbapenemase) and NDM (New Delhi metallo-beta-lactamase).