Different Phenotypic Methods for Detection of Beta Lactam Resistance in Escherichia coli

Document Type : New and original researches in the field of Microbiology.

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Microbiology Unit of Clinical Pathology Department, Faculty of Medicine, Assiut University

Abstract

Background: Beta- lactam resistant Escherichia coli is a major cause of both nosocomial and community-acquired infections. It is essential to detect the beta lactam resistance for proper antibiotic therapy and to limit the spread the infection. Objectives: The study was designed to review the rates of extended-spectrum β-lactamases (ESBL), metallo beta lactamases (MBL) beta lactamase and AmpC production among E.coli isolates and to assess the best phenotypic method for detection of the resistance. Methodology: This study included 200 isolates obtained from patients admitted to different departments in Assiut university hospital .Screening and phenotypic confirmatory tests for resistance were done. Results: The Percentages of B –Lactamase enzymes in 5o isolates of E.coli were 6 (12%) isolates not resistant by screening with antibiotic sensitivity tests, 3 (6%) isolates were negative by the gold standard phenotypic tests, 12 (24%) were ESBL alone, 2 (4%) were ESBL and AmpC, 10 (20%) were AmpC alone, 8 (16%) were ESBL and Carbapenemases and 9 (18%) were carbapenemases alone. The combined disk test showed high sensitivity and specificity in detection of ESBL and MB, For AmpC detection; the disk approximation test showed higher sensitivity and specificity than boronic acid in detection of AmpC. Conclusion: The rate of Beta lactamases production in E.coli is seriously increased, the ESBL showed the highest percentage among E.coli isolates. The phenotypic confirmatory tests showed high sensitivity and specificity and proved to be reliable methods for detection of the beta lactamase resistance, genotypic tests are recommended to be a gold standard tests to increase the specificity of the phenotypic tests.

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