Carbapenem–resistant bacteria are resistant to carbapenem antibiotics. These Gram-negative bacteria are usually from the genera known as Klebsiella, Enterobacter, Escherichia, but other genera also become resistant to carbapenems. Bacteria are highly adaptive organisms. Carbapenem antibiotics are broad-spectrum beta-lactam-type antibiotics that are especially effective against Gram-negative bacteria. Carbapenem antibiotics were introduced in the early 1980s and were seen as the last line of defence against Gram-negative bacteria that had become resistant to multiple other antibiotics. Examples of carbapenem antibiotics include imipenem, meropenem, ertapenem and doripenem. Over time, Gram-negative bacteria developed resistance to carbapenem antibiotics. They have gained the ability to either break down carbapenems with an enzyme (“carbapenemases”), or to prevent the antibiotic from entering its cell or to transport it out of the cell. In this way, carbapenem antibiotics can no longer kill these bacteria. The problem is that now, infections with these Gram-negative bacteria are essentially untreatable.