A multiresistant clone of Pseudomonas aeruginosa sequence type 773 spreading in a burn unit in Orumieh, Iran SABER YOUSEFI, 1,2 MOHAMMAD REZA NAHAEI, 3,4 SAFAR FARAJNIA, 5 MOHAMMAD AGHAZADEH, 3 AINA IVERSEN, 2 PETRA EDQUIST, 6 MAKAOUI MAA ˜ TALLAH 2 and CHRISTIAN G. GISKE 2 1 Department of Microbiology, Immunology and Genetics, Faculty of Medicine, Urmia University of Medical Sciences, Urmia, Iran; 2 Department of Clinical Microbiology L2:02, Karolinska Institutet-MTC, Karolinska University Hospital Solna, Stockholm, Sweden; 3 Microbiology Department, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz; 4 Drug Applied Research Center, Tabriz University of Medical Sciences, Tabriz; 5 Biotechnology Research Center, Tabriz University of Medical Sciences, Tabriz, Iran; and 6 Swedish Institute for Infectious Disease Control, Stockholm, Sweden Yousefi S, Nahaei MR, Farajnia S, Aghazadeh M, Iversen A, Edquist P, Maa˜tallah M, Giske CG. A multiresistant clone of Pseudomonas aeruginosa sequence type 773 spreading in a burn unit in Orumieh, Iran. APMIS 2012. Herein, we describe the phenotypic and genotypic characterization of a multiresistant clone of Pseudomonas aeruginosa disseminating in a burn unit in Orumieh, Iran. A total of 58 isolates of P. aeruginosa were collected during August 2007 and June 2008. Minimum inhibitory concentrations (MICs) of P. aeruginosa isolates were determined against 11 antimicrobial agents by E test. Serotyp- ing, pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing (MLST) were used for studying the clonal relationship among the isolates. Antibiotic susceptibility testing revealed that most of the isolates were multidrug resistant and colistin was the antibiotic with the highest activity. Pseudomonas aeruginosa isolates fell into nine different serotypes, and O10 and O11 were the most common. PFGE analyses showed 12 different genotypes and 68.1% of isolates showed more than 80% similarity, indicating possible clonal relatedness. These isolates were found to belong to the same sequence type, ST773. This sequence type has earlier been reported from China, and a double locus variant of this ST has been found earlier in France in a PER-1 extended-spectrum b-lactam- ase-producing P. aeruginosa. Key words: PFGE; multidrug resistance; serotyping; sequence type; MLST. Christian G. Giske, Clinical Microbiology L2:02, Karolinska Institutet- MTC, Karolinska Univer- sity Hospital Solna, SE-17176 Stockholm, Sweden. e-mail: christian.giske@karolinska.se Pseudomonas aeruginosa is an important nosocomial pathogen responsible for a broad spectrum of infections, particularly in burn and intensive care units (ICUs). Multiple mechanisms of antimicrobial resistance have been described in P. aeruginosa including AmpC and class A b-lactamases, metallo- b-lactamases, the expression of several efflux pumps, and alterations of porins (OprD). Interplay of these mechanisms has led to the emergence of multidrug-resistant (MDR) P. aeruginosa strains (1). Multidrug-resistant P. aeruginosa infections are difficult to treat, and the increasing prevalence of such organisms is a global health problem (2). The MDR P. aeruginosa is usu- ally defined as non-susceptible to at least three Received 21 December 2011. Accepted 20 February 2012 1 APMIS © 2012 The Authors APMIS © 2012 APMIS DOI 10.1111/j.1600-0463.2012.02948.x