However, there are no complete assays available to confirm and specify carbapenemases correctly because carbapenemase-producing bacteria, notably , 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 β-lactamases (e.g., Amp C) or extended-spectrum β-lactamases (ESBLs) that operate with or without carbapenemase activity (1–4).
Moreover, phenotypic assays cannot specify types within each class of carbapenemases, such as IMP, VIM, NDM, SIM, and GIM in MBLs (1–4).
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 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 carbapenemase [KPC]), class B (metallo-β-lactamases [MBLs], such as IMP, VIM, and NDM), and class D (OXA carbapenemases, such as OXA-23 and OXA-48) (1, 2).
A simple and rapid alternative method is thus needed to confirm carbapenemase presence in bacteria.
In Japan, IMP MBL is the most prevalent transmissible carbapenemase, particularly members of the IMP-1 group (9, 10), while KPC is quite rare and OXA-48 has not been reported (11). This assay is easy to perform and rapid (≤20 min required), requires no special equipment, and detects the 24 established IMP types.
Statistically significant differences were evaluated by comparing 95% confidence intervals of the corresponding areas.
Receiver operating characteristic (ROC) curves and the area under the ROC curve with its standard error were used to analyze the IC assay, DDST, and MHT method results, using PCR results for IMP as the gold standard.
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 ).
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.