Klebsiella pneumoniaecarbapenemases (KPCs) are plasmid-encoded Amber class A carbapenemases that can be found in K pneumoniae and other Enterobacteriaceae species including Escherichia coli. They were first identified in K pneumoniae isolates in North America in 1996 and are currently the most common type of carbapenemase found in the United States.
Metallo- β-lactamase (MBL) is a carbapenemase that confers resistance to β-lactams such as cephamycins and carbapenems as well as to clavulanic acid, sulbactam, and tazobactam. Some MBLs also cause resistance to aztreonam.2 The New Delhi metallo-β-lactamase-1 (NDM-1) is a type of MBL which was first reported in 2009 when found in a K pneumoniae strain and an E coli strain from a Swedish patient repatriated from a New Delhi hospital. Many other cases have been reported since, indicating rapid spread of these strains. NDM-1 isolates are not common in the United States.
The OXA-type carbapenemases demonstrate weaker carbapenemase activity than the other carbapenemases, but when combined with other resistance mechanisms, they may convey carbapenem resistance.3 OXAs can affect efficacy of a wide variety of β-lactams. OXA impact on clavulanic acid efficacy is relatively weak.