Extended-spectrum β-lactamases （ESBLs） are the main cause of resistance to the third and forth-generation cephalosporins in Enterobacteriaceae, which are mediated by plasmids and can hydrolyze oxyiminoaminothiazoly...Extended-spectrum β-lactamases （ESBLs） are the main cause of resistance to the third and forth-generation cephalosporins in Enterobacteriaceae, which are mediated by plasmids and can hydrolyze oxyiminoaminothiazolyl cephalosporins and monobactams. Most of ESBLs are mutants of the classical TEM and SHV types, with one or more amino-acid substitution（s） in the active site.展开更多
Two Klebsiella pneumoniae isolates （Kpcl and Kpc2） were obtained from liver samples of seven dead chickens and identified with Vitek-32 automated identification system. Antimicrobial susceptibilities were determined...Two Klebsiella pneumoniae isolates （Kpcl and Kpc2） were obtained from liver samples of seven dead chickens and identified with Vitek-32 automated identification system. Antimicrobial susceptibilities were determined by the microdilution broth method. Detection of genes encoding class A β-lactamases was performed by PCR amplification, and cloning of the ESBL gene was by plasmid restriction and fragments ligation. Conjugation assay, transformation experiments and plasmid profile analysis were performed. The incompatibility group of ESBL-carrying plasmid was determined by the PCR-based replicon typing method. Lastly, the genetic environment was analysed by direct sequencing of the DNA surrounding the ESBL gene. The genes associated with tetracycline and gentamicin resistance were also sought by PCR. The results revealed that the ESBL phenotype-negative strain Kpc2 only showed resistance to ampicillin, amoxicillin, tetracycline, and doxycycline and carried bla TEM-1 and tet（A） genes. The ESBL-producing strain Kpcl exhibited multidrug resistant phenotype and harbored bla TEM-1 , bla CTX-M-14, tet（A）, tet（B）, and rmtB genes. K. pneumoniae Kpcl contained four plasmids with molecular sizes of approximately 59, 6.9, 2.8, and 1.6 kb, but only a 59-kb plasmid, carried bla TEM-1 and blac CTM-14 genes, was observed in its transconjugant. The incompatibility group of plasmid carrying blaCTX-M-14 gene could not be determined. The bla CTX-M-14 gene was flanked upstream by an ISEcpl insertion sequence and downstream by an IS903 element. This work shows that CTX-M-14 is present in K. pneumoniae isolates from chickens in China. The bla CTX -M-4 gene was associated with an upstream ISEcpl insertion sequence. Our results underline the need for continuous surveillance of the prevalence and evolution of this CTX-M-type β-lactamase in China.展开更多
基金This work was supported by a grant from the National Natural Science Foundation of China (No. 30070903).
文摘Extended-spectrum β-lactamases （ESBLs） are the main cause of resistance to the third and forth-generation cephalosporins in Enterobacteriaceae, which are mediated by plasmids and can hydrolyze oxyiminoaminothiazolyl cephalosporins and monobactams. Most of ESBLs are mutants of the classical TEM and SHV types, with one or more amino-acid substitution（s） in the active site.
基金funded by the National Natural Science Foundation of China (31072170)
文摘Two Klebsiella pneumoniae isolates （Kpcl and Kpc2） were obtained from liver samples of seven dead chickens and identified with Vitek-32 automated identification system. Antimicrobial susceptibilities were determined by the microdilution broth method. Detection of genes encoding class A β-lactamases was performed by PCR amplification, and cloning of the ESBL gene was by plasmid restriction and fragments ligation. Conjugation assay, transformation experiments and plasmid profile analysis were performed. The incompatibility group of ESBL-carrying plasmid was determined by the PCR-based replicon typing method. Lastly, the genetic environment was analysed by direct sequencing of the DNA surrounding the ESBL gene. The genes associated with tetracycline and gentamicin resistance were also sought by PCR. The results revealed that the ESBL phenotype-negative strain Kpc2 only showed resistance to ampicillin, amoxicillin, tetracycline, and doxycycline and carried bla TEM-1 and tet（A） genes. The ESBL-producing strain Kpcl exhibited multidrug resistant phenotype and harbored bla TEM-1 , bla CTX-M-14, tet（A）, tet（B）, and rmtB genes. K. pneumoniae Kpcl contained four plasmids with molecular sizes of approximately 59, 6.9, 2.8, and 1.6 kb, but only a 59-kb plasmid, carried bla TEM-1 and blac CTM-14 genes, was observed in its transconjugant. The incompatibility group of plasmid carrying blaCTX-M-14 gene could not be determined. The bla CTX-M-14 gene was flanked upstream by an ISEcpl insertion sequence and downstream by an IS903 element. This work shows that CTX-M-14 is present in K. pneumoniae isolates from chickens in China. The bla CTX -M-4 gene was associated with an upstream ISEcpl insertion sequence. Our results underline the need for continuous surveillance of the prevalence and evolution of this CTX-M-type β-lactamase in China.
