Mădălina Maria Muntean1,2,3, Andrei-Alexandru Muntean1,2,3, François Guerin4,5, Vincent Cattoir4,5,6, Elodie Creton1,7,8,9, Garance Cotellon1,7,8,9, Saoussen Oueslati1,7,8,9, Mircea Ioan Popa2,3, Delphine Girlich1,8,9, Bogdan I Iorga10, Rémy A Bonnin1,8,9, Thierry Naas1,7,8,9. 1. TeamRESIST, INSERM U1184, School of Medicine, Université Paris-Saclay, LabEx LERMIT, Le Kremlin-Bicêtre, France. 2. The "Carol Davila" University of Medicine and Pharmacy, Bucharest, Romania. 3. The "Cantacuzino" National Medico-Military Institute for Research and Development, Bucharest, Romania. 4. CHU de Rennes, Service de Bactériologie-Hygiène Hospitalière, Rennes, France. 5. CNR de la Résistance aux Antibiotiques ("laboratoire associé Entérocoques"), Rennes, France. 6. Université de Rennes 1, Inserm U1230, Rennes, France. 7. Bacteriology-Hygiene unit, Assistance Publique/Hôpitaux de Paris, Bicêtre Hospital, Le Kremlin-Bicêtre, France. 8. French National Reference Center for Antibiotic Resistance: Carbapenem-resistant Enterobacterales, Le Kremlin-Bicêtre, France. 9. Joint research Unit EERA "Evolution and Ecology of Resistance to Antibiotics", Institut Pasteur-APHP-Université Paris Sud, Paris, France. 10. Université Paris-Saclay, CNRS, Institut de Chimie des Substances Naturelles, Gif-sur-Yvette, France.
Abstract
OBJECTIVES: Detection of carbapenemase-producing Enterobacterales (CPEs) is sometimes difficult with AmpC-hyperproducing Enterobacterales (AHEs), as they may falsely be classified as CPEs. Here, we present a rapid Carbapenem Inactivation Method (rCIM) optimized for AmpC producers (rCIM-A) that allows rapid and easy discrimination between AHEs and CPEs. METHODS: Enterobacterales (n = 249), including natural AmpC producers, AHEs, CPEs and non-carbapenemase-producing carbapenem-resistant control strains were evaluated, using Carba NP, rCIM and rCIM-A. The rCIM-A differs from the rCIM by the addition of cloxacillin (400 μg/mL) to the initial antibiotic incubation step. RESULTS: The rCIM-A yielded a sensitivity and specificity of 84.26% (95% CI: 76.00%-90.55%) and 99.29% (95% CI: 96.11%-99.98%), respectively, while those of the rCIM were 86.11% (95% CI: 78.13%-92.01%) and 80.85% (95% CI: 73.38%-86.99%), respectively; those of Carba NP were lower at 84.04% (95% CI: 75.05%-90.78%) and 91.37% (95% CI: 85.41%-95.46%), respectively, due to indeterminate results. The rCIM-A was capable of discriminating between AHEs and true CPEs, but still failed to identify OXA-23-producing Proteus mirabilis isolates and remained only partially reliable for identifying IMI-like producers and a few MBL (2 NDM-1, 1 LMB-1, 1 TMB-1 and 1 IMP-13) producers. One chromosomally encoded AmpC variant, MIR-10, gave repeatedly positive results using all three tests and was thus considered a false positive. CONCLUSIONS: Specificity for AHEs greatly improved with the rCIM-A without altering the test performance for the other resistance mechanisms. It may replace the rCIM as a cheap, easy, rapid and accurate CPE detection test.
OBJECTIVES: Detection of carbapenemase-producing Enterobacterales (CPEs) is sometimes difficult with AmpC-hyperproducing Enterobacterales (AHEs), as they may falsely be classified as CPEs. Here, we present a rapid Carbapenem Inactivation Method (rCIM) optimized for AmpC producers (rCIM-A) that allows rapid and easy discrimination between AHEs and CPEs. METHODS: Enterobacterales (n = 249), including natural AmpC producers, AHEs, CPEs and non-carbapenemase-producing carbapenem-resistant control strains were evaluated, using Carba NP, rCIM and rCIM-A. The rCIM-A differs from the rCIM by the addition of cloxacillin (400 μg/mL) to the initial antibiotic incubation step. RESULTS: The rCIM-A yielded a sensitivity and specificity of 84.26% (95% CI: 76.00%-90.55%) and 99.29% (95% CI: 96.11%-99.98%), respectively, while those of the rCIM were 86.11% (95% CI: 78.13%-92.01%) and 80.85% (95% CI: 73.38%-86.99%), respectively; those of Carba NP were lower at 84.04% (95% CI: 75.05%-90.78%) and 91.37% (95% CI: 85.41%-95.46%), respectively, due to indeterminate results. The rCIM-A was capable of discriminating between AHEs and true CPEs, but still failed to identify OXA-23-producing Proteus mirabilis isolates and remained only partially reliable for identifying IMI-like producers and a few MBL (2 NDM-1, 1 LMB-1, 1 TMB-1 and 1 IMP-13) producers. One chromosomally encoded AmpC variant, MIR-10, gave repeatedly positive results using all three tests and was thus considered a false positive. CONCLUSIONS: Specificity for AHEs greatly improved with the rCIM-A without altering the test performance for the other resistance mechanisms. It may replace the rCIM as a cheap, easy, rapid and accurate CPE detection test.