Evaluation of the carbapenem inactivation method (CIM) for detecting carbapenemase activity in enterobacteria
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AuthorAguirre Quiñonero, A.; Cano García, María Eliecer; Gamal, D.; Calvo Alén, Jaime; Martínez Martínez, Luis
The objective of this study was to evaluate the accuracy of the CIM test in the detection of carbapenemase activity in 124 strains of Enterobacteriaceae.
A panel of 124 previously characterized Enterobacteriaceae was tested: 77 strains producing the following carbapenemase families: KPC (n = 14), GES (n = 22), NDM (n = 19), VIM (n = 4), IMP (n = 4) and OXA-48 (n = 14) and 47 non-carbapenemase producers. For the CIM method, an active susceptibility meropenem disc was exposed to a bacterial suspension of a test strain; when a carbapenemase is produced, the antibiotic is inactivated allowing uninhibited growth of an indicator strain after overnight incubation. A clear inhibition zone (?20 mm) was considered indicative of no-carbapenemase activity.
All KPC, NDM, VIM, IMP or OXA-48 producing strains were unequivocally detected with the CIM test. CIM false negative results were obtained with eleven Enterobacter cloacae producing GES-6. Two other E. cloacae not producing carbapenemase (one with SHV-12, one hyperproducing AmpC) were positive by the test. The sensitivity and specificity of the assay compared to those of molecular methods were 85.7% and 95.7%, respectively.
The CIM method proved to be inexpensive and easy to interpret. It provided less than optimal results in the detection of GES-6 activity.