A Aguirre-Quiñonero1, M E Cano2, D Gamal3, J Calvo2, L Martínez-Martínez4. 1. University Hospital Marqués de Valdecilla-IDIVAL, Santander, Spain. Electronic address: amayiaguirre@gmail.com. 2. University Hospital Marqués de Valdecilla-IDIVAL, Santander, Spain. 3. Microbiology Department, Theodor Bilharz Research Institute, Cairo, Egypt. 4. University Hospital Marqués de Valdecilla-IDIVAL, Santander, Spain; Department of Molecular Biology, University of Cantabria, Santander, Spain.
Abstract
OBJECTIVES: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: The CIM method proved to be inexpensive and easy to interpret. It provided less than optimal results in the detection of GES-6 activity.
OBJECTIVES: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: The CIM method proved to be inexpensive and easy to interpret. It provided less than optimal results in the detection of GES-6 activity.