Rapid Detection of Carbapenemase-producing Enterobacteriaceae

Patrice Nordmann

, Laurent Poirel, and Laurent Dortet

Author affiliations: Faculté de Médecine Paris Sud, Le Kremlin-Bicêtre, France (P. Nordmann, L. Poirel, L. Dortet); and Institut National de la Santé et de la Recherche Médicale, Paris, France (P. Nordmann, L. Poirel, L. Dortet)

Abstract

To rapidly identify carbapenemase producers in Enterobacteriaceae, we developed the Carba NP test. The test uses isolated bacterial colonies and is based on in vitro hydrolysis of a carbapenem, imipenem. It was 100% sensitive and specific compared with molecular-based techniques. This rapid (<2 any="any" be="be" hours="hours" implemented="implemented" in="in" inexpensive="inexpensive" laboratory.="laboratory." may="may" p="p" technique="technique">

Multidrug resistance is emerging worldwide at an alarming rate among a variety of bacterial species, causing both community-acquired and nosocomial infections (1). Carbapenems, the last line of therapy, are now frequently needed to treat nosocomial infections, and increasing resistance to this class of β-lactams leaves the health care system with almost no effective drugs (1). However, reports of carbapenem-resistant Enterobacteriaceae have increased (2,3). Resistance may be related to association of a decrease in bacterial outer-membrane permeability, with overexpression of β-lactamases with no carbapenemase activity or to expression of carbapenemases (2,4,5). Spread of carbapenemase producers is a relevant clinical issue because carbapenemases confer resistance to most β-lactams (2). Various carbapenemases have been reported in Enterobacteriaceae, such as the following types: Klebsiella pneumoniae carbapenemase (KPC; Ambler class A); Verona integron–encoded metallo-β-lactamase (VIM), imipenemase (IMP), New Delhi metallo-β-lactamase (NDM) (all Ambler class B); and oxacillinase-48 (OXA-48; Ambler class D) (2,4–6). In addition, carbapenemase producers are usually associated with many other non–β-lactam resistance determinants, which give rise to multidrug- and pandrug-resistant isolates (2,3,7).
Potential carbapenemase producers are currently screened first by susceptibility testing, using breakpoint values for carbapenems (2,8). However, this technique is time-consuming, and many carbapenemase producers do not confer obvious resistance levels to carbapenems. There is a need for laboratories to search for carbapenemase producers (9). Phenotype-based techniques for identifying in vitro production of carbapenemase, such as the modified Hodge test, are not highly sensitive and specific (2,8,10). Detection of metallo-β-lactamase producers (IMP, VIM, NDM) and of KPC producers may be based on the inhibitory properties of several molecules but requires additional expertise and time (usually an extra 24–48 hours) (2,8,11,12). Furthermore, no inhibitors are available for detecting OXA-48–type producers that are spreading rapidly, at least in northern Africa, the Middle East, and Europe (2). Molecular detection of carbapenemase genes remains costly and requires substantial expertise. Both the phenotype-based techniques and molecular tests are time-consuming (at least 12–24 hours) and are poorly adapted to the clinical need for isolating patients rapidly to prevent nosocomial outbreaks.
We developed a novel test, described here, based on a technique designed to identify the hydrolysis of the β-lactam ring of a carbapenem. This test is rapid, sensitive and specific, and adaptable to any laboratory in the world.