Comparison of three phenotypic methods for the screening of carbapenem resistance among clinical isolates of Enterobacteriaceae

Abstract

Background: The global use, misuse, and abuse of broad-spectrum antibiotics coupled with failure of development of newer effective antibiotics have led to the rapid spread of carbapenemase producing Gram-negative Enterobacteriaceae. The lack of capacity for effective diagnosis results in increased morbidity, prolonged hospitalization, suboptimal treatment leading to treatment failure, and increased healthcare cost. Aims/objectives: We set out to determine the best method(s) for the phenotypic screening of carbapenem resistance among the species of Enterobacteriaceae at University of Maiduguri Teaching Hospital (UMTH). Materials and Methods: We screened all patients admitted into various wards/units of UMTH over a 6-month period to isolate Enterobacteriaceae. We used an interviewer-administered questionnaire to obtain some basic information from the patients. We confirmed the species of Enterobacteriaceae using Microbact Gram-negative 24E test kit. All confirmed isolates were screened for carbapenem resistance with Meropenem and Ertapenem antibiotic discs (10 μg, Oxoid, UK) according to the Clinical and Laboratory Standards Institute (CLSI) guideline. Minimum inhibitory concentration (MIC) using Etest of Imipenem (Biomeriux) was also determined based on CLSI recommendations. Modified Hodge test method was considered as a gold standard for confirmatory test. The three methods were compared with the gold standard. Results: We isolated 225 Enterobacteriaceae from 225 patients. Klebsiella pneumoniae had the highest proportion of 73 (32.4%). The sensitivity of the different methods in increasing order was 95.7% for Meropenem disk (10 μg), 100% for Ertapenem disk (10 μg), and 100% for Imipenem MIC. Conclusion: In view of cost and availability, the Ertapenem disc (10 μg) method can be used for the screening of carbapenem-resistant Enterobacteriaceae. For the routine screening of carbapenem resistance Enterobacteriaceae in our clinical laboratories, the Ertapenem disc (10 μg) method is recommended.