Acta Tropica 113 (2010) 20–25 Contents lists available at ScienceDirect Acta Tropica journal homepage: www.elsevier.com/locate/actatropica Characterization of antimicrobial resistance and integrons among Escherichia coli isolated from animal farms in Eastern China Liming Lu a,b,1 , Lei Dai a,1 , Yang Wang a , Congming Wu a , Xia Chen a , Lin Li c , Yonghua Qi a,d , Lining Xia a,e , Jianzhong Shen a,∗ a National Center for Veterinary Drug Safety Evaluation, College of Veterinary Medicine, China Agricultural University, Beijing, China b National Key Laboratory of Protein Engineering and Plant Gene Engineering, College of Life Sciences, Peking University, Beijing, China c College of Animal Science and Technology, Anhui Agricultural University, Hefei, Anhui, China d College of Animal Science and Technology, Henan Institute of Science and Technology, Xinxiang, Henan, China e College of Veterinary Medicine, Xinjiang Agricultural University, Urmuqi, China article info Article history: Received 22 June 2009 Received in revised form 27 August 2009 Accepted 31 August 2009 Available online 8 September 2009 Keywords: Escherichia coli Antimicrobial resistance Integron Gene transfer abstract A total of 182 Escherichia coli isolates from animals, environment and workers of dairy cattle, swine and chicken farms in Shandong which locates in Eastern China, were investigated for antimicrobial resistance as well as prevalence and the transfer mechanisms of integrons. The results revealed isolates from swine and chicken farm exhibited high levels of resistance to antimicrobial agents. The positive rate of gene cassette of class 1 integron in dairy cattle, swine and chicken farms was 5%, 20% and 41.94%, respectively. Only four isolates possessed class 2 integron, all of which were from chicken farm. Nine distinct cassette arrays were detected and two novel gene cassette arrays yheS-yheR-kefB and chrA-sul1-qacE1- orf5-aadA5-dfrA17 were identified in class 1 integron for the first time. Class 1 integrons were found to be located mostly in both chromosomal and conjugative plasmid through southern hybridization and conjugation. PFGE revealed clonal relatedness among the isolates from different sources, especially within the same farm. The results confirmed the antimicrobial resistance and prevalence of integrons were strongly associated with the selection pressure of antimicrobial agents, and resistance genes in animal farms were probably spread by both vertical and horizontal transfer. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The dissemination of antimicrobial resistance genes among bac- teria is an increasingly serious problem throughout the world. Since enterobacteria of human and animal origins constitute an enor- mous reservoir of resistance genes for commensal and pathogenic bacteria, the level of antimicrobial resistance of the enterobacte- ria is considered a good indicator for selection pressure exerted by antimicrobial agents use (Murray, 1992) and development of resis- tance in pathogens (Lester et al., 1990). Resistant bacteria from the intestinal flora of food animals can contaminate carcasses of slaugh- tered animals and thus transfer resistance genes to the microflora of humans via the food chain (Skovgaard, 2007). Investigation of antimicrobial resistance of certain indicator bacteria derived from animal and human sources such as Escherichia coli in the intesti- nal tract forms part of surveillance programs on the prevalence of antimicrobial resistance (Van Den Bogaard and Stobberingh, 2000). ∗ Corresponding author. Tel.: +86 10 62732803; fax: +86 10 62731032. E-mail address: sjz@cau.edu.cn (J. Shen). 1 Liming Lu and Lei Dai contributed equally to this work. Mobile genetic elements such as integrons, which are found in both chromosomal and extra chromosomal DNA and have spe- cific structures and abilities to capture resistant gene cassettes by a site-specific recombination system (Bennett, 1999; Hall and Collis, 1995), have shown to play important roles in the develop- ment and dissemination of multidrug-resistance (MDR) genes in Gram-negative bacteria (Carattoli, 2001; Hall, 1997; Liebert et al., 1999). A number of studies have investigated the prevalence of antimicrobial-resistant bacteria from various sources in many countries or areas (Guerra et al., 2006; Mathew et al., 1999; Moura et al., 2007; Sayah et al., 2005). Dairy cattle, swine and chick- ens are the major food-producing animals and Shandong province which locates in Eastern China is one of the most important food–animal producing and exporting area in China. However, lit- tle is known about the antimicrobial resistance patterns and gene cassette arrays of isolates from these animal farms, and direct com- parison of the antimicrobial resistance profiles and integrons of animal farms under different selection pressure of antimicrobial agents has not been reported in China. In this study, antimicrobial resistance and integrons of E. coli isolates from animals, environ- ment and workers of dairy cattle, swine and chicken farms which 0001-706X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.actatropica.2009.08.028