Genotypes ofβ-lactamase in Klebsiella pneumoniae isolates and induction and inhibition of theβ-lac-tamase gene expression

Abstract

Objective To investigate the predominant genotypes of β-lactamase in Klebsiella pneu-moniae isolates and the mechanism of antibiotic and histidine kinase inhibitor in affecting β-lactamase gene expression .Methods Tube dilution method and E-test were used to detect the susceptibility of K.pneumon-iae isolates to β-lactam antibiotics .The major genotypes of β-lactamase in β-lactam antibiotic-resistant iso-lates were identified by PCR and sequencing method .Disk diffusion test was performed to analyze the activity ofβ-lactamase .The effects of cefotaxime and histidine kinase inhibitor closantel on the expression of β-lac-tamase gene were evaluated by real-time fluorescent quantitative RT-PCR.Results All of the 118 β-lactam antibiotic-resistant K.pneumoniae isolates expressed β-lactamase, 90.7%（107/118） of which were KPC-2, TEM-1, CTX-M-14, SHV-11 and/or OXA-1 gene positive.The positive rates of TEM-1 （71.0%） and SHV-11 （64.5%） were significantly higher than that of the other three genotypes （ P〈0.05）.68.2%（73/107） of the isolates possessed two or more than two β-lactamase genotypes, and 30.8%（33/107） iso-lates were identified as TEM-1＋SHV-11 genotype.Except for KPC-2 mRNA, the levels of TEM-1, SHV-11, CTX-M-14 and OXA-1 mRNA were significantly up-regulated by cefotaxime at MIC/4 （P〈0.05）, but were inhibited by 100μmol/L closantel （P〈0.05）.Conclusion TEM-1 and SHV-11 are the majorβ-lactamase genotypes carried by K.pneumoniae strains isolated from Zhejiang area , and TEM-1 plus SHV-11 （ TEM-1＋SHV-11） is the predominant carrying mode of the β-lactamase genotypes .Sublethal dose of cefotaxime can enhance the expression of β-lactamase genes in K.pneumoniae, while the histidine kinase inhibitor , closan-tel, can block the increased expression of β-lactamase genes induced by cefotaxime . Key words: Klebsiella pneumoniae ; β-lactamase genotype; Gene expression ; Regulatory mechanism