Research Article Phenotypic and Molecular Characterization of Plasmid Mediated AmpC -Lactamases among Escherichia coli, Klebsiella spp., and Proteus mirabilis Isolated from Urinary Tract Infections in Egyptian Hospitals Mai M. Helmy 1,2 and Reham Wasfi 2 1 Department of Microbiology & Immunology, Faculty of Medicine, Zagazig University, Zagazig, Sharqia, Egypt 2 Department of Microbiology and Immunology, Faculty of Pharmacy, October University for Modern Sciences and Arts (MSA), 26 July Road Intersection with El Wahat Road, 6th of October, Giza, Egypt Correspondence should be addressed to Reham Wasfi; rwasfi@msa.eun.eg Received 14 February 2014; Revised 16 May 2014; Accepted 18 May 2014; Published 9 June 2014 Academic Editor: Frederick D. Quinn Copyright © 2014 M. M. Helmy and R. Wasfi. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. e incidence of resistance by Enterobacteriaceae to -lactam/-lactamase inhibitors combination is increasing in Egypt. ree phenotypic techniques, comprising AmpC disk diffusion and inhibition dependent methods using phenylboronic acid (PBA) and cloxacillin, were compared to PCR based method for detection of plasmid mediated AmpC -lactamase in common urinary tract isolates. A total of 143 isolates, including E. coli, Klebsiella pneumonia, and Proteus mirabilis, were collected from urinary tract infections cases in Egyptian hospitals. Plasmid encoded AmpC genes were detected by PCR in 88.46% of cefoxitin resistant isolates. e most prevalent AmpC gene family was CIT including CMY-2, CMY-4, and two CMY-2 variants. e second prevalent gene was DHA-1 which was detected in E. coli and Klebsiella pneumonia. e genes EBC, FOX, and MOX were also detected but in small percentage. Some isolates were identified as having more than one pAmpC gene. e overall sensitivity and specificity of phenotypic tests for detection of AmpC -lactamase showed that AmpC disk diffusion and inhibition dependent method by cloxacillin were the most sensitive and the most specific disk tests. PCR remains the gold standard for detection of AmpC -lactamases. is study represents the first report of CMY-2 variants of CMY-42 and CMY-102 -lactamase-producing E. coli, Klebsiella pneumonia, and Proteus mirabilis isolates in Egypt. 1. Introduction AmpC -lactamases have gained importance for over than forty years, since their discovery, as one of the enzymes responsible for antimicrobial resistance in Gram-negative bacilli. AmpC -lactamases are either plasmid or chromo- somal mediated. Citrobacter freundii, Enterobacter cloacae, Morganella morganii, Hafnia alvei, and Serratia marcescens are organisms having chromosomally mediated AmpC - lactamases. In late 1980s plasmid-borne AmpC cephalospori- nases were detected that appear to be genetic descendants of the chromosomally encoded AmpC enzymes [1]. e presence of such genes on plasmids facilitated their spread between the family of Enterobacteriaceae as Klebsiella spp., Escherichia coli, Proteus mirabilis, and Salmonella spp. [2]. e increased presence of plasmid mediated AmpC (pAmpC) -lactamases worldwide is becoming of great concern [2]. AmpC -lactamases are characterized by their ability to inac- tivate cephamycins in addition to other extended-spectrum cephalosporins and being resistant to clavulanic acid [3]. Infections caused by AmpC-positive bacteria are of particular clinical and epidemiological importance and cause higher patient morbidity and mortality [4, 5]. In Gram-negative organisms, the detection of AmpC- mediated resistance is problematic as phenotypic techniques may give misinterpreted results and, consequently, treatment Hindawi Publishing Corporation BioMed Research International Volume 2014, Article ID 171548, 8 pages http://dx.doi.org/10.1155/2014/171548