The research was carried out by Guo-Bao Tian and colleagues at the Bioengineering Research Center for Animal Disease Prevention and Control, '985 Project' Science Innovative Platform for Resource and Environment Protection of Southwestern, School of Life Science at Sichuan University in Chengdu.

The aim of the study was to investigate the antibiotic resistance profiles and the molecular epidemiology of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli isolates from two production swine operations in Sichuan province between August 2002 and February 2007.

The prevalence of ESBL-producing E. coli increased dramatically from 2.2 per cent to 10.7 per cent 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 harboured ESBL genes. Among them, 13 harboured blaCTX-M-15/22 and one harboured blaSHV-2.

The authors believe that this is the first study to identify blaCTX-M-22 from production animals. One isolate in 2002 harboured blaSHV-2, indicating that ESBL genes have been present in farm animals in China since at least 2002. Molecular characterisation 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–beta-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.

Reference

Guo-Bao Tian, Hong-Ning Wang, Li-Kou Zou, Jun-Ni Tang, Ying-Wang Zhao, Man-Yu Ye, Jing-Yuan Tang, Yi Zhang, An-Yun Zhang, Xin Yang, Chang-Wen Xu, Yue-Jun Fu. 2009. Detection of CTX-M-15, CTX-M-22, and SHV-2 extended-spectrum ß-lactamases (ESBLs) in Escherichia coli fecal-sample isolates from pig farms in China. Foodborne Pathogens and Disease. April 2009, 6(3): 297-304.