Detection of IMP Metallo-β-Lactamase in Carbapenem-Nonsusceptible Enterobacteriaceae and Non-Glucose-Fermenting Gram-Negative Rods by Immunochromatography Assay

Abstract

b Metallo-␤-lactamases (MBLs) are transmissible carbapenemases of increasing prevalence in Gram-negative bacteria among health care facilities worldwide. Control of the further spread of these carbapenem-resistant bacteria relies on clinical microbiological laboratories correctly identifying and classifying the MBLs. In this study, we evaluated a simple and rapid method for detecting IMP, the most prevalent MBL in Japan. We used an immunochromatography (IC) assay for 181 carbapenem-nonsusceptible (CNS) (nonsusceptible to imipenem or meropenem) strains comprising 74 IMP-producing and 33 non-IMP-producing strains of non-glucose-fermenting Gram-negative rods (NFGNR), as well as 64 IMP-producing and 10 non-IMP-producing Enterobacteriaceae strains. The IC assay results were compared to those from the double-disk synergy test (DDST), the MBL Etest, and the modified Hodge test (MHT) (only for Enterobacteriaceae). The IMP type was confirmed by specific PCR and direct sequencing. The IC assay detected all of the IMP-type MBLs, including IMP-1, -2, -6, -7, -10, -11, -19, -20, and -22 and IMP-40, -41, and -42 (new types), with 100% specificity and sensitivity against all strains tested. Although the sensitivity and specificity values for the DDST and MHT were equivalent to those for the IC assay, the MBL Etest was positive for only 87% of NFGNR and 31% of Enterobacteriaceae due to the low MIC of imipenem, causing an indeterminate evaluation. These results indicated that the IC assay might be a useful alternative to PCR for IMP MBL detection screening. The recent worldwide emergence and dissemination of carbapenemase-producing Gram-negative rods (GNR) that are resistant to carbapenems is a significant concern with respect to patient care and infection control strategies (1). The transmissible carbapenemases are divided into three different classes, class A (serine carbapenemases, such as Klebsiella pneumoniae carbapenemase [KPC]), class B (metallo-␤-lactamases [MBLs], such as IMP, VIM, and NDM), and class D (OXA carbapenemases, such as OXA-23 and OXA-48) (1, 2). Rapid and adequate detection of carbapenemases is very important for appropriate antimicrobial chemotherapies and infection control measures. Various phenotypic confirmation tests for detecting carbapenemases have been performed, including inhibition tests of carbapenemase activity, the modified Hodge test (MHT), and detection of carbapenem hydrolysis (1-8). However, there are no complete assays available to confirm and specify carbapenemases correctly because carbapenemase-producing bacteria, notably Enterobacteriaceae, show variable carbapenem MIC distributions (even under the breakpoint) and sometimes have carbapenemase-independent mechanisms, such as reduced permeability by porin alternations, active efflux pumping, and hyperproduction of class C ␤-lactamases (e.g., AmpC) or extended-spectrum ␤-lactamases (ESBLs) that operate with or without carbapenemase activity (1-4). Moreover, phenotypic assays cannot specify types within each class of carbapenemases, such a...

Carbapenemase-Producing Enterobacteriaceae Recovered from the Environment of a Swine Farrow-to-Finish Operation in the United States

“…Unlike bla KPC , which has become endemic in human health care settings in some parts of the United States (19), IMP variants have been infrequently reported in North America. Originally identified in 1988 in a Pseudomonas aeruginosa isolate collected in Japan and in Enterobacteriaceae collected in a Japanese hospital 5 years later, IMP variants are now the most prevalent transmissible carbapenemase genes in Japan and are found in multiple species of Gram-negative bacteria internationally (20). In the United States, the first occurrence of the IMP gene was reported in a P. aeruginosa isolate recovered from a tracheal aspirate of a trauma patient in the southwestern United States in 2006 (21).…”

Interspecies Dissemination of a Mobilizable Plasmid Harboring bla IMP-19 and the Possibility of Horizontal Gene Transfer in a Single Patient

“…Antimicrobial susceptibility testing was performed using the broth microdilution method with dry plates (Eiken Chemical, Tokyo, Japan) according to CLSI guidelines (10). MBL detection was phenotypically performed using a double-disk synergy test with sodium mercaptoacetate (metallo-␤-lactamase SMA Eiken; Eiken Chemical) and three commercial Kirby-Bauer (KB) disks (Eiken Chemical) containing 30 g of ceftazidime (CAZ), 10 g of imipenem (IPM), or 10 g of meropenem (MEPM) as previously described (11).…”

Phenotypic and Genotypic Methods for Determination of Carbapenemase Producing Enterobacteriaceae Isolates

“…Notake ve ark. (45) IMP enziminin hızlı saptanması amacıyla geliş-tirilmiş Quick Chaser IMP (Saga, Japan) ticari kitini değerlendirdikleri çalışmada, IMP enziminin % 100 duyarlılık ve özgüllükte saptandığını belirtmişlerdir Özgül immünolojik reaksiyon temelli olan bu yöntemde, belli bir enzimi yüksek özgüllük ve duyarlılıkta tespit edebilmek mümkündür. Bazı karbapenemaz tiplerinin endemik olduğu bölgelerde o enzime yönelik immünokromatog-rafik testlerin kullanılması verimli olabilmektedir.…”