Detection and differentiation of carbapenemase production in carbapenem-resistant Enterobacteriaceae by the novel modified Carba NP test

Abstract

There is an increasing worldwide prevalence of carbapenems resistance in Enterobacteriaceae (CRE). The production of carbapenemase is the most important drug resistance mechanism. Several phenotypic-based detecting carbapenemase enzyme methods have been developed, including the modified Hodge test (MHT), the Carba NP test, the modified carbapenem inactivation method (mCIM), and other combined disk tests. Unfortunately, these methods are unable to differentiate between types of carbapenemase. The purpose of this study was to develop and verify the modified Carba NP test for carbapenemase enzymes differentiation by supplementing the carbapenemase inhibitors (clavulanic acid and dipicolinic acid). The clinical isolates of carbapenemase-producing Enterobacteriaceae were collected from Wichianburi and Phetchabun hospitals in Phetchabun province, Thailand. These clinical isolates were then determined using phenotypic and genotypic methods. The results show that the novel modified Carba NP test showed 100% specificity. Non-susceptible carbapenem was detected in 28/173 isolates (16.2) of Enterobacteriaceae, and only 5 isolates (2.9%) of carbapenemase-producing Enterobacteriaceae were found. Genotypic analysis shows that these isolates habour the blaNDM of carbapenemase genes. Furthermore, the modified Carba NP test is considered to be an accessible method for identifying types of carbapenemase enzymes by using a microtiter plate, and the results can be interpreted within 15 and 90 minutes.