Alterations in the DNA topoisomerase IV responsible for quinolone resistance in MRSA and MRSE

我们试图确定gyrA和帕洛阿尔托研究中心基因的部分序列的临床分离株epidermidis葡萄球菌和金黄色葡萄球菌,试图评估协会gyrA和帕洛阿尔托研究中心基因突变与耐氟喹诺酮类耐甲氧西林金黄色葡萄球菌和MRSE序列分析PCR产品从65年fluoroquinolone-resistant临床分离株耐甲氧西林金黄色葡萄球菌被用来研究喹诺酮gyrA resistance-determining区域的基因和类似地区的帕洛阿尔托研究中心的基因。65株parC中80位丝氨酸（Ser 80）的变化与喹诺酮类药物耐药有关。此外，parC和gyrA突变的连续获得导致更高水平的抗性。这些数据强烈提示ParC突变和GyrA突变也是MRSA耐氟喹诺酮类药物的重要因素。检测了7个耐氟喹诺酮MRSE突变体的gyrA和parC基因突变。虽然5个突变体在ParC中有单个氨基酸变化，但两个更高水平的氟喹诺酮耐药菌株在GyrA （Ser84-Try和Asp94-Gly）中有双氨基酸变化，在ParC中有单个氨基酸变化。包括MRSE在内的表皮葡萄球菌对喹诺酮类药物耐药的最重要因素似乎是DNA旋切酶和DNA拓扑异构酶IV等靶酶的突变，以及由于药物渗透减少和/或药物外排增加而导致药物积累减少的突变。

We tried to determine partial sequences of the gyrA and parC genes of clinical isolates of Staphylococcus epidermidis and Staphylococcus aureus and attempted to assess the association of mutations in the gyrA and parC genes with fluoroquinolone resistance in MRSA and MRSE Sequence analysis of PCR products from 65 fluoroquinolone-resistant clinical isolates of MRSA was used to examine the quinolone resistance-determining regions of the gyrA gene and the analogous regions of the parC gene. The changes of the serine at position 80 (Ser 80) in parC of 65 strains ested were associated with resistance to quinolone antibacterials. Moreover, sequential acquisition of mutations in parC and gyrA led to higher levels of resistance. These data strongly suggest that ParC mutations as well as GyrA mutations are also important factor for fluoroquinolone resistance in MRSA.Seven fluoroquinolone-resistant mutants of MRSE were examined for mutations in the gyrA and parC genes. While five mutants had a single amino acid changes in ParC,two higher level fluoroquinolone-resistant isolates had a double amino acid change in GyrA (Ser84-Try & Asp94-Gly) and a single amino acid change in ParC.The most important factor for quinolone resistance in S.epidermidis including MRSE seems to be the mutations of target enzymes such as DNA gyrase and DNA topoisomerase IV,and mutations causing decreased drug accumulation due to decreased drug penetration and/or increased drug efflux.