Nagachinta Supakana, Chen Jinru
Department of Food Science and Technology, The University of Georgia, 1109 Experiment Street, Griffin, Georgia 30223-1797, USA.
J Food Prot. 2009 Jan;72(1):21-7. doi: 10.4315/0362-028x-72.1.21.
This study was undertaken to characterize the integrons present in a group of Shiga toxin-producing Escherichia coli (STEC) isolates and the ability of these integrons to transfer antibiotic resistance genes from STEC to E. coli K-12 MG1655. A total of 177 STEC isolates were analyzed for antibiotic susceptibility and the presence of integrons. Class 1 integrons were detected in 14 STEC isolates, and a class 2 integron was identified in 1 STEC isolate. The STEC isolates positive for class 1 integrons were resistant to streptomycin (MICs > 128 microg/ml) and sulfisoxazole (MICs > 1,024 microg/ml), and the isolate positive for the class 2 integron was resistant to streptomycin (MIC of 128 microg/ml), trimethoprim (MIC > 256 microg/ml), and streptothricin (MIC > 32 microg/ml). Results of restriction digestion and nucleotide sequencing revealed that the cassette regions of the class 1 integrons had a uniform size of 1.1 kb and contained a nucleotide sequence identical to that of aadA1. The class 2 integron cassette region was 2.0 kb and carried nucleotide sequences homologous to those of aadA1, sat1, and dfrA1. Results of the conjugation experiments revealed that horizontal transfers of conjugative plasmids are responsible for the dissemination of class 1 integron-mediated antibiotic resistance genes from STEC to E. coli K-12 MG1655. Antibiotic resistance traits not mediated by integrons, such as resistance to tetracycline and oxytetracycline, were cotransferred with the integron-mediated antibiotic resistance genes. The study suggested a possible role of integron and conjugative plasmid in dissemination of genes conferring resistance to antibiotics from pathogenic to generic E. coli cells.
本研究旨在表征一组产志贺毒素大肠杆菌（STEC）分离株中存在的整合子，以及这些整合子将抗生素抗性基因从STEC转移至大肠杆菌K-12 MG1655的能力。共对177株STEC分离株进行了抗生素敏感性和整合子存在情况分析。在14株STEC分离株中检测到1类整合子，在1株STEC分离株中鉴定出1个2类整合子。1类整合子阳性的STEC分离株对链霉素（MICs>128μg/ml）和磺胺异恶唑（MICs>1024μg/ml）耐药，2类整合子阳性的分离株对链霉素（MIC为128μg/ml）、甲氧苄啶（MIC>256μg/ml）和链丝菌素（MIC>32μg/ml）耐药。限制性酶切和核苷酸测序结果显示，1类整合子的盒式结构区域大小均一，为1.1 kb，且包含与aadA1相同的核苷酸序列。2类整合子盒式结构区域为2.0 kb，携带与aadA1、sat1和dfrA1同源的核苷酸序列。接合实验结果表明，接合性质粒的水平转移导致了1类整合子介导的抗生素抗性基因从STEC传播至大肠杆菌K-12 MG1655。非整合子介导的抗生素抗性性状，如对四环素和土霉素的抗性，与整合子介导的抗生素抗性基因共同转移。该研究表明整合子和接合性质粒在将赋予抗生素抗性的基因从致病性大肠杆菌细胞传播至普通大肠杆菌细胞中可能发挥作用。
