【摘要】 通过微量稀释法测定28株猪源链球菌对环丙沙星的MIC值,研究东北地区猪源链球菌对环丙沙星耐药性与parC、gyrA基因突变的相关性。通过PCR方法扩增parC和gyrA基因喹诺酮耐药决定区(QRDR)并测序分析;18株耐药菌在parC基因80位的突变(AGC→ATT)导致氨基酸Ser→Ile突变,11株高度耐药菌在gyrA基因81位的突变(CAG→CAT、CTT或CTA)导致氨基酸Ser→Ile、Phe或Tyr的突变。当菌株对环丙沙星的MIC值≤1μg/mL时,parC和gyrA基因的QRDR区均未有突变;而当MIC≥2μg/mL时,ParC的氨基酸发生了Ser80→Ile的突变,同时发生GyrA氨基酸Ser81突变的菌株,耐药水平很高。研究表明,环丙沙星低水平类耐药是由于拓扑异构酶Ⅳ改变引起,而高水平耐药是由拓扑异构酶Ⅳ、DNA旋转酶共同改变引起的。实验结果证明,在一定条件下,耐药性的高低与突变位点的多少成正比。更多还原

【Abstract】 To detect the relationship between ciprofloxacin resistance and gyrA and parC gene mutation in Streptococcus suis.The MIC of 28 strains of Streptococcus suis were determined by microdilution.Mutations in the quinolone resistance-determining regions(QRDRs) of the gyrA and parC genes were analyzed by PCR.Ser to Iie(AGC to ATT) mutation at position 80 of the parC gene was detected in 18 strains of ciprofloxacin resistance S.suis;and Ser to Ile,Phe or Tyr mutations(CAG to CAT,CTT or CTA) at the position 81 of gyrA gene were detected in 12 highly resistance strains;no amino acid changes in GyrA or parC were detected for strains with MIC of ciprofloxacin under 1 μg/mL.A single substitution in parC was found in the strains with MIC of ciprofloxacin higher than 2 μg/mL.Strains with mutation at Ser81 of gyrA had a high resistance level.Mutations in parC gene result in low level resistance against ciprofloxacin,and high level resistance is resulted from the mutations in both genes.The number of mutations is proportional to the level of ciprofloxacin resistance under certain conditions.更多还原