Carbapenemases in Enterobacteriaceae: Activity, Epidemiology, and Laboratory Detection

Abstract 

Carbapenemases are β-lactamases that confer resistance to the carbapenems (e.g., imipenem, meropenem, ertapenem, and doripenem). Most often these enzymes confer resistance to the other β-lactam agents as well, including extended-spectrum cephalosporins. The enzymes are usually found in bacterial isolates that are already resistant to nearly all other antimicrobial agents, and treatment options for infections caused by them are significantly limited. This important mechanism of resistance is emerging in the United States, and the most common enzyme is the Klebsiella pneumoniae carbapenemase (KPC). The KPC enzyme is found in many different genera of Enterobacteriaceae, but most commonly in K. pneumoniae. Currently, KPC-producing isolates are commonly isolated in the northeastern part of the U.S., but reports of isolates from other locations are increasing. Prevention and control of this emerging resistance is complicated by the occurrence of KPC-positive isolates producing low-level carbapenem resistance that is hard to detect in the clinical microbiology laboratory. The most sensitive methods for detecting carbapenemase-producing isolates are to look for elevated but susceptible carbapenem susceptibility results. In addition to discussing KPC, this article will review the epidemiology of other carbapenemases and their potentials for dissemination in the U.S.