Submitted to: Antimicrobial Chemotherapy
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/8/2009
Publication Date: 12/1/2009
Publication URL: http://handle.nal.usda.gov/10113/57273
Citation: Du, X., Wu, C., Liu, H., Li, X., Beier, R.C., Xiao, F., Qin, S., Huang, S., Shen, J. 2009. Plasmid-mediated ArmA and RmtB 16S rRNA methylases in Escherichia coli isolated from chickens. Antimicrobial Chemotherapy. 64:1328-1330. Interpretive Summary: Aminoglycosides are a group of antibiotics widely used in China for the prevention and control of Escherichia coli bacterial infections in chickens. High-level aminoglycoside resistance has been increasingly reported among various bacteria related to E. coli obtained from food animals. The resistance is a result of the bacterial production of a specific chemical called 16S rRNA methylase. This investigation was conducted in the Henan Province of China, and the study investigated the presence of the 16S rRNA methylase in E. coli bacteria isolated from chickens. High-level resistance to the aminoglycoside antibiotic amikacin was found in 12 of the 120 bacterial isolates tested. These 12 bacterial isolates also produced the 16S rRNA methylase responsible for the resistance to amikacin. This study reports the emergence of high-level aminoglycoside resistance in E. coli bacteria isolated from chickens in the Henan Province of China.
Technical Abstract: 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.