Mechanisms of Quinolones Resistance in Escherichia coli / 中华医院感染学杂志

ABSTRACT

OBJECTIVE To study the mechanisms of quinolones resistance in Escherichia coli.METHODS Forty E.coli clinical isolates were randomly collected from clinical specimens at the Tianjin First Central Hospital from Mar 2004 to Dec 2005.Then we detected the susceptibility to antibiotics in 40 clinical isolates of E.coli by MICs and K-B disk diffusion method.In order to investigate the mutations in the target genes,we amplified the QRDR of gyrA and parC by PCR.Later we analyzed the PCR products by single strand conformation polymorphism analysis(SSCP).In the meantime,the PCR products of marOR region were sequenced to detect the possible gene changes which contributed to the increasing expression of MarA and then lead to the Mar phenotype.RESULTS The alterations in gyrA were found in all quinolones-resistante strains.Asp87→Asn and Ala84→Pro were found besides the common amino acid alteration.The alterations in parC were found in thirty-six strains resistant to quinolones.There were no parC alterations in ECO24 which was nalidixic acid-resistant and ofloxacin/gatifloxacin-susceptible.ECO11 Which was resistant to quinolones only had no gene changes in marOR region.Six gene changes in marOR region were found in ECO5 which was resistant to mutiple antibodies.The alteration in 1879 bp changed the terminator.CONCLUSIONS The alterations in gyrA and parC are responsible for the resistant phenotypes in E.coli.That is,the alterations in the gyrA are primarily responsible for resistance to quinolones,and the alterations in the parC may play a complemental role in enhancing resistance to fluoroquinolones.Moreover,the randomly collected strains resistant to quinolones,have found some mutations in marOR.It may be play certain roles in multiple antibiotic resistance of E.coli.