The prevalence of plasmid-mediated AmpC β-lactamases among clinical isolates of Escherichia coli and Klebsiella pneumoniae from five children’s hospitals in China
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The purpose of this study was to investigate the prevalence of plasmid-mediated AmpC β-lactamases in Escherichia coli and Klebsiella pneumoniae from five children’s hospitals in China. A total of 494 E. coli and 637 K. pneumoniae isolates were collected from five children’s hospitals in China from 2005 to 2006. The isolates with decreased susceptibility to cefoxitin were subjected to confirmation test with 3-aminophenyl boronic acid. Polymerase chain reaction (PCR) amplification of the blaAmpC, blaTEM, blaCTXM, and blaSHV genes and their gene sequencing were performed. Transconjugants were achieved by conjugation experiments. Plasmid-mediated AmpC β-lactamases were found in 10.1% of K. pneumoniae (64/637) and in 2.0% of E. coli (10/494) strains. The proportion of plasmid-mediated AmpC-producing strains significantly increased from 2005 (2.6%) to 2006 (9.3%) (p<0.001). The DHA-1-producing isolates were the most prevalent type (93.2%, 69/74). The sequences of blaDHA-1 genes were all identical to those from the GenBank. Strains of blaCMY-2 were isolated from five isolates (6.8%), which were all from E. coli. One sequence of blaCMY-2 differs from blaCMY-2 in the GenBank. Eighteen of the 74 (24.3%) AmpC-producing K. pneumoniae and E. coli isolates coproduced an extended-spectrum β-lactamase (ESBL). Cefoxitin resistance was transferred to 15 of the 74 positive strains (20.3%). Our study has demonstrated the occurrence of plasmid-mediated AmpC β-lactamases in E. coli and K. pneumoniae in Chinese pediatric patients and DHA-1 type AmpC enzymes had the highest prevalent rate. The CMY-2 AmpC β-lactamases from the children’s hospitals in China in this study are the first reported. Hence, continuous surveillance of the prevalence and evolution of AmpC β-lactamase is important.
KeywordsCefoxitin Multiplex Polymerase Chain Reaction Cefepime Cefoperazone AmpC
This work was supported by a grant (no. 2004BA720A09–01) from the Health Ministry of China. We would like to thank all of the participating hospitals for their support. We also thank Dingxia Shen, the 301 Hospital of Chinese People Library Army, for graciously supplying the strain of E. coli J53AzR and the control strains, and Lin Yuan, for his assistance in this work.
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