Evaluation of the β-CARBA™ test, a colorimetric test for the rapid detection of carbapenemase activity in Gram-negative bacilli.
There is an urgent need for accurate and fast diagnostic tests to identify carbapenemase-producing bacteria. Here, we have evaluated a novel colorimetric test (the β-CARBA™ test; Bio-Rad) to detect carbapenemase-producing Gram-negative bacilli from cultured colonies.



The performance of the β-CARBA™ test was compared with that of the Carba NP test (or the CarbAcineto NP test) and RAPIDEC ® CARBA NP (bioMérieux) using a collection of 290 isolates with characterized β-lactamase content. This collection included 199 carbapenemase producers (121 Enterobacteriaceae, 36 Pseudomonas and 42 Acinetobacter baumannii ) and 91 non-carbapenemase producers (55 Enterobacteriaceae, 20 Pseudomonas and 16 A. baumannii ).



The β-CARBA™ test correctly detected 84.9% of the carbapenemase producers, including all KPC and IMP, 96.4% of VIM, 85.3% of NDM, 80.5% of OXA-48-like and 91.2% of A. baumannii -related OXA carbapenemases (OXA-23, OXA-40, OXA-58, OXA-143 and overexpressed OXA-51). All rare metallo-β-lactamases (SPM, AIM, GIM, DIM and SIM) were detected. Importantly, all non-KPC Ambler class A carbapenemases were not detected, including GES variants with carbapenemase activity ( n  = 6), IMI ( n  = 3), NMC-A ( n  = 1), SME ( n  = 2), FRI-1 ( n  = 1) and BIC-1 ( n  = 1). All non-carbapenemase producers gave a negative result except with OXA-163-, OXA-405- and one TEM-3-producing Citrobacter freundii . The overall sensitivity and specificity of the β-CARBA™ test were 84.9% and 95.6%, respectively. This test is easy to perform and to interpret by non-specialized staff members.



Despite lack of specificity towards non-KPC Ambler class A and OXA-48-like carbapenemases, the β-CARBA™ test could complete the existing panel of tests available for the confirmation of carbapenemases in Gram-negatives.
Associated French National Reference Center for Antibiotic Resistance, Le Kremlin-Bicêtre, France.|Joint research Unit EERA 'Evolution and Ecology of Resistance to Antibiotics', Institut Pasteur - APHP - Université Paris Sud, Paris, France.
Sandrine
S
Bernabeu
Associated French National Reference Center for Antibiotic Resistance, Le Kremlin-Bicêtre, France.|Joint research Unit EERA 'Evolution and Ecology of Resistance to Antibiotics', Institut Pasteur - APHP - Université Paris Sud, Paris, France.
Laurent
L
Dortet
Associated French National Reference Center for Antibiotic Resistance, Le Kremlin-Bicêtre, France.|Joint research Unit EERA 'Evolution and Ecology of Resistance to Antibiotics', Institut Pasteur - APHP - Université Paris Sud, Paris, France.
Thierry
T
Naas
D040981:Acinetobacter baumannii / Q000187:drug effects / Q000201:enzymology* / Q000302:isolation & purification; D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology; D001426:Bacterial Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D001431:Bacteriological Techniques; D015780:Carbapenems / Q000378:metabolism / Q000494:pharmacology; D002863:Chromogenic Compounds / Q000737:chemistry; D016971:Citrobacter freundii / Q000187:drug effects / Q000201:enzymology; D003124:Colorimetry / Q000379:methods*; D004755:Enterobacteriaceae / Q000187:drug effects / Q000201:enzymology* / Q000302:isolation & purification; D006801:Humans; D006868:Hydrolysis; D008826:Microbial Sensitivity Tests; D011549:Pseudomonas / Q000187:drug effects / Q000201:enzymology* / Q000302:isolation & purification; D012680:Sensitivity and Specificity; D001618:beta-Lactamases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D015780:Carbapenems; D002863:Chromogenic Compounds; D001618:beta-Lactamases; C063912:carbapenemase