Prevalence and transmission of oqxAB gene in clinical strains of Escherichia coli and Klebsiella pneumoniae / 中国感染与化疗杂志

ABSTRACT

Objective To investigate the prevalence and the transmission of oqxAB gene in clinical strains of Escherichia coli and Klebsiella pneumoniae .Methods Nonduplicate clinical isolates of E.coli (n=72)and K .pneumoniae (n=49)were col-lected.The oqxAB gene was amplified by PCR.The product was sequenced.Plasmid conjugation experiments were done in oqxAB-positive E.coli and K.pneumoniae strains to detemine whether oqxAB gene is located in plasmid.The MICs and mu-tant prevention concentrations (MPCs)for ciprofloxacin were determined in transconjugants with oqxAB gene by agar dilution method.Results The oqxA,oqxB and oqxAB were identified in 15,4,and 7 of the 72 strains of Escherichia coli and 4,1,and 34 of the 49 strains of K.pneumoniae,respectively.The oqxAB gene was positive in 2 (2/16)ciprofloxacin sensitive and 5 (5/56)ciprofloxacin resistant E.coli strains,in 8 (8/14)ciprofloxacin sensitive and 26 (26/35)ciprofloxacin resistant K. pneumoniae strains,respectively.The E.coli and K.pneumoniae strains with or without oqxAB did not show different sus-ceptibility to ciprofloxacin.The oqxA and oqxB sequences from E.coli and K.pneumoniae showed 99% similarity to the se-quences of GeneBank accession number AB601773.1 and accession number FJ975561.1,respectively.The oqxAB gene was successfully transferred in 4 of the 5 oqxAB-positive E.coli strains.The MIC of ciprofloxacin was 0.25-0.5 mg/L against the transconjugants,31-62 times higher than the MICs for the recipient strains.The MPC of ciprofloxacin was 8-16 mg/L against the transconjugants,32 times higher than that for recipient strain J53.The oqxAB gene were not transferred in K. pneumoniae. When the MIC of ciprofloxacin was ≤0.062 5 mg/L,the MPC of ciprofloxacin was 0.25-0.5 mg/L for K.pneumoniae strains with or without oqxAB.When MIC was 0.25-0.5 mg/L,the MPC of ciprofloxacin was 2-16 mg/L for K .pneumoniae strains with or without oqxAB .Conclusions oqxAB gene is present in E .coli and K .pneumoni-ae .The oqxAB gene spreads through plasmid in E .coli.The nonsiginificant difference of oqxAB prevalence between ciproflox-acin sensitive and ciprofloxacin resistant strains indicates that oqxAB gene may mediate low level resistance to ciprofloxacin in E.coli.The E.coli transconjugants of oqxAB gene can produce high level resistance under the selection pressure of ciproflox-acin.The high level resistance in K .pneumoniae under selection pressure of ciprofloxacin is not associated with oqxAB gene, but related to the ciprofloxacin MIC against these strains.