Comparison of Carba NP-Direct, Carbapenem Inactivation Method, and β-CARBA Tests for Detection of Carbapenemase Production in Enterobacteriaceae

Rapid and accurate detection of carbapenemase-producing isolates are extremely important for management of antimicrobial therapy and the implementation of infection control measures. We evaluated the performance of Carba NP-direct, carbapenem inactivation method (CIM), and the commercial beta-CARBA tests for detection of carbapenemase production in Enterobacteriaceae. Enterobacteriaceae isolates with previously characterized carbapenemase types (n = 110) and non-carbapenemase-producing Escherichia coli (n = 15) isolates were tested. Sensitivities of Carba NP-direct, CIM, and beta-CARBA tests were 99.0%, 92.7%, and 93.6%, respectively, while specificity was 100% for all three tests. For beta-CARBA test, a 60-min incubation time instead of 30 increased the sensitivity to 98.1%, and lessened false negativity, particularly with OXA-48-like producers. Our results showed that Carba NP-direct, CIM, and beta-CARBA tests are useful tools for the reliable detection of carbapenemase activity in enterobacterial isolates. Carba NP-direct is a simple, rapid, and low-cost test for routine use.