COMPARISON OF DIFFERENT PHENOTYPIC METHODS FOR AmpC DETECTION

BACKGROUND AmpC beta-lactamases are clinically important cephalosporinases which confer resistance to cephamycins, penicillins, aminoglycosides and beta-lactam-beta-lactamase inhibitor combinations and produced in several Enterobacteriaceae. The aim of this study was to compare various phenotypic detection methods of AmpC beta-Lactamases. MATERIALS AND METHODS This was a descriptive study. Three hundred multidrug-resistant bacterial isolates were tested for AmpC beta-lactamase enzyme production. Cefoxitin (30 mu g) resistance was used as the screening test for AmpC enzyme detection. Phenotypic confirmation was done by conventional disk combination method (Cefoxitin/cefoxitin + boronic acid), 3D extract method, double disk synergy test (DDST) and AmpC disk test. RESULTS All 300 strains were found to be AmpC positive by the screening test. Out of these 300 strains, 100 strains were positive by disk combination method, 107 strains by DDST, 111 strains by 3D extract method and 170 strains by AmpC disk test. CONCLUSION Cefoxitin resistance can be used as the screening test for AmpC. AmpC disc test is simple to perform. Many strains can be checked on single petri plate and get best results in comparison to other methods of AmpC detection. So, it can be used as a phenotypic method for detection of AmpC enzyme production in resource-limited settings, where genotypic detection methods are not available.