Performance of chromIDA (R) CARBA medium for carbapenemases-producing enterobacteriaceae detection during rectal screening

Chromogenic chromIDA (R) CARBA medium was compared with CDC method and MacConkey agar with imipenem for its performance in detecting carbapenemase-producing Enterobacteriaceae (CPE) during a faecal screening surveillance program. Double rectal swabs were collected from patients hospitalized in the ICU. One swab was inoculated onto the solid media chromIDA (R) CARBA and MacConkey agar with imipenem, while the other was tested according to CDC protocol. Suspected colonies from all procedures were identified to species level and tested for their susceptibility to carbapenems by phenotypic tests. All carbapenem non-susceptible isolates were tested by the modified Hodge test (MHT) and synergy tests. Positive results were confirmed by PCR testing for carbapenemase gene detection. Performance of all three procedures applied was statistically analyzed as compared to MHT and PCR results for the presence of carbapenemase-encoding genes. Out of 177 rectal samples tested, 86 samples were found to contain one or more CPE verified by molecular detection of carbapenemase encoding genes among isolated Enterobacteriaceae. Sensitivity of chromIDA (R) CARBA was 96.5 % in clinical samples. Specificity was 91.2 % at the reading level and 100.0 % after Gram staining. chromIDA (R) CARBA performed with high accuracy among the phenotypic methods applied, giving early results.