Prevalence and Detection of Amp C β- Lactamase Resistance in Gram Negative Uropathogens

The most common mechanism of resistance in Gram negative bacteria is by the production of ß lactamases which inactivate ß lactam antibiotics. Among which Amp C β lactamases are more important because they confer resistance to Cephalosporins, β lactam β lactamase inhibitor combinations and Aztreonam. Although reported with increasing frequency, the true rate of occurrence of AmpC β-lactamases  remains unknown. The present study was designed to determine the occurrence of AmpC enzyme-harboring Gram-negative uropathogens in a tertiary care hospital.  A total of 430 consecutive, non repeat urinary Gram negative isolates were included in the present study. All the 430 isolates were screened for AmpC β-lactamase production by Novel predictor disk placement method. Isolates positive in the screening were further confirmed by inhibitor based Cefoxitin –Cloxacillin disk diffusion test. Sixty eight (16%) isolates were positive for AmpC β-lactamases. Based on the species 36 (14%) Esch.coli ,27 (28%) Klebsiella pneumoniae, 2 (6%) Pseudomonas aeruginosa  1 (5%) Citrobacter freundii, 1 (8%)Acinetobater sp and 1 (33%)Enterobacter aerogens harbored AmpC enzymes. All the isolates were sensitive to imepenam. This study has shown the occurrence of Amp C β lactamase producing Gram negative urinary isolates in our hospital.  Failure to identify Amp C β lactamase producers may lead to inappropriate antimicrobial treatment . Inhibitor based  Cefoxitin -Cloxacillin  disk diffusion test is easier to perform routinely to detect Amp C β lactamase production.

Key words: Gram negative uropathogens, drug resistance,  Amp C β-lactamases