Prevalence and Characterization of Class 1 Integrons in Escherichia coli of Poultry and Human Origin Alexandra Vasilakopoulou, 1,2 Mina Psichogiou, 1 Leonidas Tzouvelekis, 3 Panayiotis T. Tassios, 3 Chris Kosmidis, 1 George Petrikkos, 1 Eleftheria S. Roma, 1 Ekaterina Charvalos, 4 Maria Passiotou, 5 Athina Avlami, 2 and George L. Daikos 1 Abstract A prospective study was conducted to determine the prevalence and the gene-cassette content of class 1 integrons in Escherichia coli of poultry and human origin. A total of 235 E. coli isolates were examined; 65 were derived from farm poultry, 80 from hospitalized, and 90 from nonhospitalized patients. Susceptibilities to a range of antimicrobial agents were determined by disk diffusion. Int1-specific polymerase chain reaction, conserved-segment polymerase chain reaction, and DNA sequencing were used to determine the presence, length, and content of integrons. The relatedness among the isolates was examined by pulsed-field gel electrophoresis of XbaI digests of genomic DNA. The integron carriage rate for poultry isolates was 49.2%, whereas the carriage rate for hospital isolates was 26.2% and for community 11.1%. Multidrug resistance (resistance to three or more classes of antibiotics) phenotypes were observed in 96.8% of the integron-positive isolates, whereas only 34.9% of non- integron-carrying organisms were multidrug resistant ( p < 0.001). Seven integron types ranging in size from 663 to 2674 bp were identified; six types were observed in poultry isolates, five in hospital, and three in community isolates. Each integron type carried a distinct gene-cassette combination. The most prevalent gene cassettes be- longed to the aad and dfr families. Identical integrons were detected in E. coli of human and poultry origin. A large reservoir of integrons exists in E. coli of poultry origin. The horizontal transfer of class 1 integrons among bacteria of poultry and human origins may contribute in the dissemination of antimicrobial resistance. Introduction T he routine administration of antimicrobial agents to animals as a means of treating and preventing diseases or promoting growth may contribute to the emergence of anti- microbial-resistant organisms that are subsequently trans- ferred to humans (O’Brien, 2002). Notwithstanding the drastic reduction in the use of antimicrobial agents as growth pro- moters in food-producing animals, several studies suggest an unremitting flow of antimicrobial resistance from animals to humans, via the food chain (Klare et al., 1995; Stobberingh et al., 1999; Fabrega et al., 2008). Transmission of antimicrobial resistance from animal to humans can occur either by dis- semination of a resistant bacterial clone or by horizontal transfer of resistance determinants. A link between resistant organisms of animal and human origin can be easily con- firmed for truly enteric pathogens, such as Campylobacter and Salmonella (Endtz et al., 1991; Threlfall, 2002). The complex routes of transmission of resistance determinants, however, from animal to human via commensal bacteria, such as Es- cherichia coli, are difficult to elucidate. A substantial proportion of resistance determinants in Gram-negative bacilli reside on class 1 integrons that are ca- pable of capturing and expressing resistance genes contained in cassette-like structures (Fluit and Schmitz, 1999, 2004). Moreover, the frequent association of integrons with mobile elements such as transposons and transferable plasmids al- lows their spread across different species. Thus, class 1 in- tegrons are potential vehicles for transferring resistance genes from animal to human bacteria (Kang et al., 2005). Herein, we examined the class 1 integron content of E. coli isolates derived from farm poultry in Greece. These integrons 1 First Department of Propaedeutic Medicine, Laiko General Hospital, Athens, Greece. 2 Department of Clinical Microbiology, Laiko General Hospital of Athens, Athens, Greece. 3 Department of Microbiology, National and Kapodistrian University of Athens, Athens, Greece. 4 Technological Institute of Athens, Athens, Greece. 5 Veterinary Laboratory of Chalkis, Chalkis, Greece. FOODBORNE PATHOGENS AND DISEASE Volume 6, Number 10, 2009 ª Mary Ann Liebert, Inc. DOI: 10.1089=fpd.2009.0281 1211