LAUSR

The increasing spread of carbapenemase-producing Gramnegative bacteria represents one of the major public health problems. The main carbapenemases identified in clinical isolates belong to different structural types of β-lactamases belonging to three different classes: the Klebsiella pneumoniae Carbapenemase (KPC) enzymes belong to the class A, the New Delhi Metallo-β-lactamase (NDM), the Verona integron-encoded metallo-β-lactamase (VIM) and the imipenemase (IMP) enzymes belong to the class B, and the OXA-48-types belong to the class D. One of the most efficient ways to limit the dissemination of carbapenemaseproducing isolates is their early detection in patients being infected or colonized, to rapidly implement adequate control measures. Recent and rapid carbapenemase detection tests are currently available and are based on the biochemical detection of the carbapenem hydrolysis [1, 2]. Recently, an immunochromatographic detection test, the NG-test Carba 5 (NG Biotech, Guipry, France), has been developed. This lateral flow technique allows the detection of the five main carbapenemase types, i.e., KPC, IMP, VIM, NDM, and OXA-48types (OXA-48, OXA-162, OXA-181, OXA-204, OXA-232, and OXA-244). This kit detects most of the variants of these families except the class D carbapenemases OXA-23, OXA40, and OXA-58 that are identified in Acinetobacter spp. isolates. As part of the mission of our national reference center in Switzerland, we have evaluated this test with a collection of carbapenemase-producing Enterobacteriaceae and non-Enterobacteriaceae isolates, and additionally with double-carbapenemase producers that may be also identified. We tested a collection of 73 carbapenem-resistant Gramnegative bacilli. This collection included 45/73 Enterobacteriaceae (Citrobacter freundii, Enterobacter aerogenes, Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Proteus mirabilis, and Serratia marcescens), 11/73 Acinetobacter baumannii and 17/73 Pseudomonas aeruginosa. The isolates of the collection were resistant to carbapenems due to different mechanisms: (1) production of a carbapenemase (OXA-48-types n = 15, KPC n = 9, NDM n = 13, VIM n = 14, IMP n = 9, OXA-23 n = 23, OXA-40 n = 2 and OXA-58 n = 2), (2) overproduction of a cephalosporinase associated with permeability defects (n = 4) or (3) impermeability alone (n = 3) (Table 1). Noteworthy, four isolates co-produced two carbapenemases (NDM-1 and OXA-48-types) (Table 1). All carbapenemase genes were identified by PCR experiments followed by sequencing. All isolates were grown on URISelectTM 4 agar plates (Bio-Rad, Cressier, Switzerland) for 16 h at 37 °C. The NG-test Carba 5 kit was used according to the manufacturer’s recommendations. Briefly, one colony was mixed with five drops of lysis buffer included in the test and 100 μl of the lysis suspension was added to the immunological lateral flow cassette. The results were obtained after 15 min of incubation at room temperature and are reported in Table 1. The NG-test Carba 5 kit allowed the identification of all KPC, OXA-48-types, NDM, VIM and IMP-producers. Noteworthy, this test was able to detect both carbapenemases in the isolates co-producing both NDM-1 and OXA-48-types. As expected, this test cannot detect the most important carbapenemases in A. baumannii * Patrice Nordmann [email protected]