Abstract
The aim of the present study was to investigate the antibiotic resistance profiles and the molecular epidemiology of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli isolates from two production swine operations in Sichuan Province, China, between August 2002 and February 2007. The prevalence of ESBL-producing E. coli increased dramatically from 2.2% to 10.7% during this period. This increase appeared mostly related to dissemination of CTX-M–type ESBLs among E. coli isolates. Of 212 E. coli isolates studied, 14 harbored ESBL genes. Among them, 13 harbored bla CTX-M-15/22 and one harbored bla SHV-2. To our knowledge, this is the first study to identify bla CTX-M-22 from production animals. One isolate in 2002 harbored bla SHV-2, indicating that ESBL genes have been present in farm animals in China since at least 2002. Molecular characterization and pulsed-field gel electrophoresis of the ESBL-producing isolates suggested that different mechanisms may be involved in the dissemination of the CTX-M genes and revealed that additional resistance determinants for non–β-lactam antibiotics were carried by plasmids encoding certain ESBL genes. Results of this study provide an example of how ESBL genes, particularly those of CTX-M lineages, are rapidly spreading among E. coli isolates from commercial pig farms in Sichuan province of China.