en Anti-microbial agents, resistance and treatment protocols Anti-microbial agents, resistance and treatment protocols Original article Original article <strong>Introduction:</strong> Multidrug-resistant (MDR) <em>Pseudomonas aeruginosa </em>isolates are among the common cause of Nosocomial infections. In<em> P. aeruginosa </em>infections, several genes, <em>mex</em>A, and <em>mex</em>B are involved in resistance to antibiotics and <em>psl</em>A, <em>pel</em>A and <em>brl</em>R contribute to biofilm formation. This study aims to investigate the prevalence of these genes in <em>P. aeruginosa </em>isolates and to determine their relationship with biofilm formation, antibiotic resistant, pigment production, and source of infection. <strong>Methods:</strong> We collected 63 specimens out of 90 samples from patients hospitalized in a hospital affiliated to Shiraz University of Medical Sciences. The specimens belonged to 42 men and 21 women and included urine, sputum, wound, skin, blood, body fluid, and central venous blood (CVB). The samples were cultured on solid media and diagnosed according to standard phenotypic characteristics. Disk diffusion method was used to identify the clinical MDR<em> P. aeruginosa</em> isolates, and the genes <em>psl</em>A, <em>pel</em>A, <em>brl</em>R, <em>mex</em>A, and <em>men </em>were detected by PCR detected. <strong>Results:</strong> about 25.4% of the clinical isolates were MDR, <em>i.e</em>., resistant to three or more antibiotics. The prevalence of the genes in the clinical isolates was as follows: <em>psl</em>A (92.1%), <em>pel</em>A (68.3%), <em>brl</em>R (93.7%), <em>mex</em>A (95.2%) and <em>mex</em>B (50.8%). The highest and lowest prevalence of drug resistance belonged to ceftriaxone and amikacin, respectively. The highest MDR <em>P. aeruginosa</em> isolates originated from wound, urine and sputum specimens. <strong>Conclusion:</strong> The presence of MDR isolates correlated significantly with the patients&rsquo; gender, the origin of specimens, and bacterial pigment production.&nbsp; In this study, the detected genes did not significantly correlate with the MDR features of the isolates. <em>J Med Microbiol Infec Dis, 2018, 6 (2): 5 pages. </em><br> &nbsp;<br> &nbsp; Pseudomonas aeruginosa, Multidrug resistance, Biofilm genes, Shiraz, Iran. 72 76 http://jommid.pasteur.ac.ir/browse.php?a_code=A-10-171-1&slc_lang=en&sid=1 Maryam Motevasel motevaselm10@gmail.com 0000-0002-7983-1629 No Department of Pathobiology, School of Veterinary Medicine, Shiraz University, Shiraz, Iran Masoud Haghkhah mhaghkha@shirazu.ac.ir 0000-0001-7266-4082 Yes Department of Pathobiology, School of Veterinary Medicine, Shiraz University, Shiraz, Iran