THE INTERNATIONAL ARABIC JOURNAL OF ANTIMICROBIAL AGENTS ISSN 2174-9094 © Under License of Creative Commons Attribution 3.0 License 1 2015 Vol. 5 No. 3:1 doi: 10.3823/773 iMedPub Journals http://journals.imed.pub This article is available from: www.iajaa.org / www.medbrary.com PMQR determinants among clinical isolates of ESBL and Amp C producing Serratia marcescens in Mansoura University Hospitals: A 6-year study 1 Medical Microbiology and Immunology Department. 2 Public health and Community Medicine, Faculty of Medicine, Mansoura University, Mansoura, Egypt Corresponding author: Enas Hammad, MD  enashammad@yahoo.com Enas Hammad 1 , Randah Helal 2 Abstract Background: Plasmid mediated quinolone resistant determinants (PMQRs) are found to be of clinical relevance because it causes decreased susceptibility to quinolones which are valuable antibiotics against intrinsically resistant Serratia marcescens. This study aimed to determine the occurrence of PMQR determinants (qnr, aac(6′)-Ib- cr and qep) and their relation with extended-spectrum β-lactamase (ESBL) and / or Amp C- producing S. marcescens. Material and Method: One hundred and eleven S. marcescens were tested for resistance to five quinolones by disc diffusion method. Testing for qnr, aac(6′)-Ib-cr and qep was carried out by multiplex PCR, while ESBL and Amp C production were evaluated by double disc synergy test and cefoxitin Hodge test, respectively. Results: A total of 51/111 (45.9%) S. marcescens were resistant to one or more of the tested quinolones. Among S. marcescens isolates, 13 (11.7%) were ESBL producers and 5 (4.5%) were Amp C producers. Multiplex PCR confirmed the presence of PMQR determinant in 14 (12.6%) of S. marcescens isolates and these were positive for qnrA and qnr B in 3 and 10 of the isolates, respectively, whereas one isolate co- harbored aac(6’)-Ib-cr and qnrA. Among 13 ESBL producers, 3 and 5 isolates were positive for qnrA and qnr B, respectively (8/13; 61.5%),whereas one isolate which has co-expressed aac(6’)-Ib-cr and qnrA was associated with Amp C production (1/5;20%).