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Plasmid-mediated ArmA and RmtB 16S rRNA methylases in Escherichia coli isolated from chickens

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Aminoglycosides are widely used antibiotics in China for the prevention and control of Escherichia coli infections in chickens. High-level aminoglycoside resistance mediated by the production of 16S rRNA methylase has been increasingly reported among various Gram-negative pathogens. Previously, only two studies have identified 16S rRNA methylase genes in food animals (pigs). Here we investigated E. coli obtained from chickens in Henan Province, China, for the presence of six 16S rRNA methylase genes: armA, rmtA, rmtB, rmtC, rmtD, and npmA. The E. coli isolates were screened by polymerase chain reaction (PCR), and 12 of the 120 isolates had high-level amikacin resistance and also contained the armA or rmtB genes. Genetic relationships of the 12 isolates were evaluated by Pulsed Field Gel Electrophoresis (PFGE), and seven major pulsotypes were observed among these 12 isolates, suggesting that both horizontal and vertical transfer of genes could have played an important role in the dissemination of the 16S rRNA methylase genes. Genes could be transferred among the armA- and rmtB-positive isolates by conjugation and electroporation, respectively. Hybridization revealed that the genes were localized on two differently sized digest fragments, and one isolate contained two copies of the armA gene. The genetic environment surrounding the armA and rmtB genes was investigated by determining the sequences of their flanking regions. The results demonstrate a diverse genetic environment adjacent to the rmtB gene, and both the IS elements and Tn1721 transposase may play an important role in the dissemination of the rmtB gene. This study reports the emergence of the armA and rmtB genes in clinical isolates of E. coli found in chickens in China.
Xiang-Dang Du , Cong-Ming Wu , He-Bing Liu , Xin-Sheng Li , Ross C. Beier , Fang Xiao , Shang-Shang Qin , Si-Yang Huang , Jian-Zhong Shen
Escherichia coli , Escherichia infections , amikacin , antibiotic resistance , chickens , electroporation , gene transfer , genes , genetic relationships , nucleic acid hybridization , pathogens , polymerase chain reaction , pulsed-field gel electrophoresis , ribosomal RNA , China
Antimicrobial Chemotherapy 2009 v.64
Journal Articles, USDA Authors, Peer-Reviewed
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