Fluoroquinolone Resistance Among Isolates of Streptococc

2003年，从芝加哥一家三级儿科医院和一家初级儿科收集的116株临床分离株对氟喹诺酮类抗生素的耐药性进行了评估。自2003年10月以来，对11株耐药菌株进行了检测，以确定氟喹诺酮类药物的耐药机制。检测到parc和gyrA基因点突变。除了一株ParC基因没有突变，但gyrA基因突变，表明从蛋氨酸99转换为丝氨酸的菌株外，所有菌株的ParC基因都发生了突变，导致从丝氨酸79转换为丙氨酸。5株莫西沙星MIC为0.5 mg/ml的菌株均有突变，除ParC突变外，GyrA中的甲硫氨酸99还被丝氨酸取代。MIC的显著增加似乎需要ParC和gyrA的突变，导致氨基酸残基的替换。这些残基替换类似于肺炎链球菌中描述的那些。双重突变对左氧氟沙星的影响比莫西沙星更大。在左氧氟沙星变得中度耐药的菌株中，莫西沙星仍然敏感。我们目前正在寻找PAR E和gyrB基因的点突变。为了完成这项研究，我们将确定每个菌株的M型，并使用Rep-PCR和脉冲场凝胶电泳分析来确定这些菌株的亲缘关系。这项研究的结果在2004年洛杉矶新奥尔良举行的第104届美国微生物学会大会上公布。

A total of 116 clinical isolates collected from a tertiary pediatric hospital and a primary pediatric department in Chicago were evaluated for resistance to fluoroquinolone antibiotics in 2003. Since October 2003, a subset of 11 resistant strains was examined to determine the mechanism of fluoroquinolone resistance. Point mutations were detected the in parC and gyrA genes. All isolates had a mutation in the parC gene that translates to a switch from serine 79 to alanine except one isolate that had no mutation in the parC gene but had a mutation in gyrA indicating a switch from methionine 99 to serine. All 5 isolates with moxifloxacin MIC 0.5 mg/ml had a mutation that represents a replacement of methionine 99 with serine in gyrA in addition to the mutation in parC. A significant increase in MIC appears to require mutations in both parC and gyrA that result in replacement of an amino acid residue. These residue replacements are similar to those described in S. pneumoniae. The dual mutations affect levofloxacin more than moxifloxacin. Moxifloxacin remains susceptible in those isolates in which levofloxacin becomes intermediate resistant. We are currently searching for point mutations in the par E and gyrB genes. To finish this study we will have the M type determined for each isolate and we will determine the relatedness of the isolates using Rep-PCR and Pulsed Field Gel Electrophoresis analysis. Results from this study were presented at the 104th American Society for Microbiology General Meeting, 2004, New Orleans, LA.