Comparison of the Carba NP, Modified Carba NP, and Updated Rosco Neo-Rapid Carb Kit Tests for Carbapenemase Detection

Abstract

The accurate detection of carbapenemase-producing organisms is a major challenge for clinical laboratories. The Carba NP test is highly accurate but inconvenient, as it requires frequent preparation of fresh imipenem solution. The current study was designed to compare the Carba NP test to two alternative tests for accuracy and convenience. These were a modified Carba NP test that utilized intravenous (i.v.) imipenem-cilastatin, which is less expensive than reference standard imipenem powder, and an updated version of the Rosco Neo-Rapid Carb kit, which does not require the preparation of imipenem solution and has a shelf life of 2 years. The comparison included 87 isolates that produced class A carbapenemases (including KPC-2, -3, -4, -5, -6, and -8, NMC-A, and SME type), 40 isolates that produced metallo-␤-lactamases (including NDM-1, GIM-1, SPM-1, IMP-1, -2, -7, -8, -18, and -27, and VIM-1, -2, and -7), 11 isolates that produced OXA-48, and one isolate that produced OXA-181. Negative controls consisted of 50 isolates that produced extended-spectrum ␤-lactamases (ESBLs), AmpCs (including hyperproducers), K1, other limited-spectrum ␤-lactamases, and porin and efflux mutants. Each test exhibited 100% specificity and high sensitivity (Carba NP, 100%; Rosco, 99% using modified interpretation guidelines; and modified Carba NP, 96%). A modified approach to interpretation of the Rosco test was necessary to achieve the sensitivity of 99%. If the accuracy of the modified interpretation is confirmed, the Rosco test is an accurate and more convenient alternative to the Carba NP test.T he accurate detection of carbapenemase-producing organisms (CPOs) is a major challenge for clinical laboratories. In some laboratories, detection of carbapenem-resistant Enterobacteriaceae (CRE) is the primary focus, and the need to detect carbapenemase production is considered optional and for epidemiologic purposes only (1). CRE detection is based on detection of resistance or nonsusceptibility of Enterobacteriaceae to carbapenems and certain cephalosporins and does not distinguish between carbapenemase producers and non-carbapenemase producers. Although carbapenem-resistant non-carbapenemase producers are important, they should not trigger the same level of concern as CPOs such as NDM-and other carbapenemase-producing isolates (2-6). Furthermore, the focus on CRE detection ignores carbapenemase producers that either are not Enterobacteriaceae or are carbapenemase-producing Enterobacteriaceae that are carbapenem susceptible, such as the VIM-producing Klebsiella pneumoniae isolates with imipenem MICs as low as 0.12 g/ml that were involved in a large outbreak with high mortality in Greece (7).Clinical laboratories aiming to detect carbapenemase producers need a test that is accurate and convenient. The Carba NP test is highly accurate (8, 9) but labor-intensive and inconvenient due to the instability of imipenem in solution, which necessitates extemporaneous preparation (1, 10). Another disadvantage of this test is the high cost of reference...

Comparative Evaluation of Four Phenotypic Tests for Detection of Carbapenemase-Producing Gram-Negative Bacteria

“…On the other hand, the calculated analytical performances of RCNP and NRCK were lower than previously reported (9,11,14,16). At least two reasons might have accounted for those differences.…”

“…However, this high proportion of OXA-48 producers is in line with the current epidemiology of CPE observed in several European countries such as Belgium, France, Spain, or Germany (4). In comparison with this report, OXA-48 producers represented only 7.9% to 27.5% of the screened CPE isolates in other studies where better overall tests performances were reported (11,13,14,16).…”

“…The Neo-Rapid Carb kit and the Rapidec Carba NP test have been evaluated by several groups (8)(9)(10)(11)(12)(13)(14)(15)(16), but, to our knowledge, no comparison with the novel ␤ Carba test has been published yet. Evaluations of the colorimetric carbapenem hydrolysis assays have mostly focused on Enterobacteriaceae, while reports dealing with nonfermentative Gram-negative bacilli are scarce.…”

Multicenter Performance Assessment of Carba NP Test

“…In principle, the test is similar to the classic ␤-lactamase detection assays described by Escamilla and by Skinner and Wise in the 1970s, in which benzylpenicillin acidimetrically produced a red color after hydrolysis by Haemophilus influenzae ␤-lactamase (1, 2). With the Carba NP test, hydrolysis of imipenem produces acid and drives the pH indicator, phenol red, from red to yellow.The Carba NP test has been studied by several investigators (3-14), including evaluations and comparisons to a commercial version (15)(16)(17)(18)(19)(20). However, the literature lacks consistency in the Carba NP methodology.…”

“…The Carba NP test has been studied by several investigators (3-14), including evaluations and comparisons to a commercial version (15)(16)(17)(18)(19)(20). However, the literature lacks consistency in the Carba NP methodology.…”