Use of a modified disc diffusion test to detect ampc beta lactamase production in escherichia coli from cases of urinary tract infections

Abstract

Routine detection of AmpC beta lactamases in Escherichia coli is cumbersome.  This study was performed to determine the usefulness of a modified disc diffusion test to detect AmpC beta lactamases in E.coli.  28 non-repetitive, cefoxitin resistant isolates of E.coli were collected from cases of urinary tract infections and screened phenotypically for ESBLs and AmpC beta lactamase using DDST (ceftazidime and ceftazidime-clavulanic acid for detection of ESBLs, cefoxitin-cloxacillin DDST and cefoxitin - phenylboronic acid, cefoxitin-EDTA combination discs). Genotypic detection of AmpC and ESBL genes was done by PCR along with mutation analysis of chromosomal promoter of AmpC. Of the 28 isolates, 6 strains showed enhancement of zone of inhibition in cefoxitin-cloxacillin, cefoxitin plus 400mcg of phenyl boronic acid and a combination of 400 mcg of phenyl boronic acid and 292 mcg of EDTA but not with EDTA alone.  Of the 6 phenotypically AmpC beta lactamase positive strains, 4 carried plasmid AmpC beta lactamase gene.