Evaluation of phenotypic tests to detect carbapenem-resistant Enterobacteriaceae in colonized patients hospitalized in intensive care units

In this study, we aimed to evaluate the performance of different phenotypic tests to detect carbapenem-resistant Enterobacteriaceae. Three different phenotypic methods were evaluated: (1) combined-disk test of meropenem plus phenylboronic acid or EDTA reading after 24 h and 48 h; (2) selective/chromogenic read after 24 h and after 48 h; and (3) overnight selective enrichment broth containing 10 μg ertapenem disk followed by culture on MacConkey agar. A positive result in at least one of the methods was submitted to PCR for bla(NDM-1), bla(OXA-48), bla(KPC), bla(SPM-1), bla(IMP), and bla(GES) detection. Carbapenem-resistant Enterobacteriaceae was detected in 31 (30.4%) of 102 rectal swabs evaluated. All isolates showed to be KPC-2-producing organisms. Results showed excellent agreement among the evaluated tests (positive and negative) (kappa = 0.88). It is important to state that combined-disk test with phenylboronic acid is not suitable for bacterial identification/isolation. Conversely, selective/chromogenic agar after 48h of incubation showed to be a useful tool, with the advantage of presumptive bacterial identification.