Detection methods of Enterobacteriaceae producing extended spectrum betalactamase

Production of extended-spectrum beta-lactamases (ESBL) considered one of the most important resistance mechanisms that impair antimicrobial treatment of infections caused by Enterobacteriaceae. Four phenotypic methods were compared to detect ESBL production; the tests based on the synergy between a third-generation cephalosporin and clavulanate. These tests are: the double-disk synergy test (DDST) 25 to 30mm, DDST (30mm), DDST (20mm) and the double-disk (Spanish- test). In our study, we worked on 81 strains of ESBL enterobacteriaceae. Synergy test 25 to 30 mm, could detect 90.12% of ESBLs strains. So if we had known the best distance which we will clearly detected the "champagne cork" appearance, we practiced synergy test at 30mm. This test highlighted ESBL production in only 17 (20.99%) strains. distance reduction between C3G disks and clavulanate disk to 20 mm led to detect 73 (90.12%). Double disk test (Spanish test) detected 81 (100%), this test confirms the presence of ESBLS. By comparison with other tests, this test had the highest rate of ESBLS. In most cases; standard disk diffusion tests are effective, and still recommended for ESBL detection in routine laboratories. Nevertheless, it is worth combining standard disk diffusion test with other approaches, such as modified disk tests or E tests.