title: A combined disk test for direct differentiation of carbapenemase-producing enterobacteriaceae in surveillance rectal swabs.
abstract: Carbapenemase-producing Enterobacteriaceae (CPE) are rapidly spreading worldwide. Early detection of fecal CPE carriers is essential for effective infection control. Here, we evaluated the performance of a meropenem combined disk test (CDT) for rapidly differentiating CPE isolates directly from rectal swabs. The screening method was applied for 189 rectal swabs from hospitalized patients at high risk for CPE carriage. Swabs were suspended in 1 ml saline and cultured for confluent growth onto a MacConkey agar plate with a meropenem (MER) disk alone, a MER disk plus phenyl boronic acid (PBA), a MER disk plus EDTA, and a MER disk plus PBA and EDTA. An inhibition zone of ≤ 25 mm around the MER disk alone indicated carriage of carbapenem-resistant organisms. Furthermore, ≥ 5-mm differences in the inhibition zone between MER disks without and with the inhibitors (PBA, EDTA, or both) were considered positive results for detecting Klebsiella pneumoniae carbapenemase (KPC), metallo-β-lactamase (MBL), or both carbapenemases, respectively. For comparison, rectal suspensions were tested using MacConkey plates with ertapenem (MacERT) disks and PCR (PCR-S) for carbapenemase genes. Of the 189 samples, 97 were genotypically confirmed as CPE positive by one of the three protocols tested. The CDT, MacERT disks, and PCR-S assays exhibited sensitivities of 94.8%, 96.9%, and 94.8% and specificities of 100%, 98.9%, and 100%, respectively, for detecting CPE-positive swabs. Moreover, the CDT correctly differentiated the production of KPC, MBL, or both carbapenemases in 78 of the 97 (80.4%) CPE-positive rectal swabs. Our results demonstrate that the CDT may provide a simple and inexpensive method for detecting and differentiating the carbapenemase type within a single day without requiring further testing and additional delay, supporting the timely implementation of infection control measures.
authors.affiliation: Department of Microbiology, Medical School, University of Athens, Athens, Greece. spournaras@med.uoa.gr
authors.forename: Spyros
authors.initials: S
authors.lastname: Pournaras
authors.forename: Olympia
authors.initials: O
authors.lastname: Zarkotou
authors.forename: Aggeliki
authors.initials: A
authors.lastname: Poulou
authors.forename: Ioulia
authors.initials: I
authors.lastname: Kristo
authors.forename: Georgia
authors.initials: G
authors.lastname: Vrioni
authors.forename: Katerina
authors.initials: K
authors.lastname: Themeli-Digalaki
authors.forename: Athanassios
authors.initials: A
authors.lastname: Tsakris
mesh_terms: D001426:Bacterial Proteins / Q000032:analysis*; D015780:Carbapenems / Q000494:pharmacology*; D003365:Costs and Cost Analysis; D004755:Enterobacteriaceae / Q000187:drug effects / Q000201:enzymology* / Q000302:isolation & purification; D062665:Epidemiological Monitoring; D005243:Feces / Q000382:microbiology; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000191:economics / Q000379:methods; D013997:Time Factors; D001618:beta-Lactamases / Q000032:analysis*
chemical_list: D001426:Bacterial Proteins; D015780:Carbapenems; D001618:beta-Lactamases; C063912:carbapenemase