Kumar Manoj, Dahiya Sushila, Sharma Priyanka, Sharma Sujata, Singh Tej P, Kapil Arti, Kaur Punit
Department of Biophysics, All India Institute of Medical Sciences, New Delhi, India.
Department of Microbiology, All India Institute of Medical Sciences, New Delhi, India.
PLoS One. 2015 May 11;10(5):e0126560. doi: 10.1371/journal.pone.0126560. eCollection 2015.
Enteric fever is a major cause of morbidity in several parts of the Indian subcontinent. The treatment for typhoid fever majorly includes the fluoroquinolone group of antibiotics. Excessive and indiscriminate use of these antibiotics has led to development of acquired resistance in the causative organism Salmonella Typhi. The resistance towards fluoroquinolones is associated with mutations in the target gene of DNA Gyrase. We have estimated the Minimum Inhibitory Concentration (MIC) of commonly used fluoroquinolone representatives from three generations, ciprofloxacin, ofloxacin, levofloxacin and moxifloxacin, for 100 clinical isolates of Salmonella Typhi from patients in the Indian subcontinent. The MICs have been found to be in the range of 0.032 to 8 μg/ml. The gene encoding DNA Gyrase was subsequently sequenced and point mutations were observed in DNA Gyrase in the quinolone resistance determining region comprising Ser83Phe/Tyr and Asp87Tyr/Gly. The binding ability of these four fluoroquinolones in the quinolone binding pocket of wild type as well as mutant DNA Gyrase was computationally analyzed by molecular docking to assess their differential binding behaviour. This study has revealed that mutations in DNA Gyrase alter the characteristics of the binding pocket resulting in the loss of crucial molecular interactions and consequently decrease the binding affinity of fluoroquinolones with the target protein. The present study assists in understanding the underlying molecular and structural mechanism for decreased fluoroquinolone susceptibility in clinical isolates as a consequence of mutations in DNA Gyrase.
肠热症是印度次大陆多个地区发病的主要原因。伤寒热的治疗主要包括氟喹诺酮类抗生素。这些抗生素的过度和滥用导致致病生物体伤寒沙门氏菌产生了获得性耐药性。对氟喹诺酮类药物的耐药性与DNA旋转酶靶基因的突变有关。我们估计了来自三代常用氟喹诺酮代表药物环丙沙星、氧氟沙星、左氧氟沙星和莫西沙星对100株来自印度次大陆患者的伤寒沙门氏菌临床分离株的最低抑菌浓度（MIC）。发现MIC范围为0.032至8μg/ml。随后对编码DNA旋转酶的基因进行了测序，并在喹诺酮耐药决定区的DNA旋转酶中观察到点突变，包括Ser83Phe/Tyr和Asp87Tyr/Gly。通过分子对接对这四种氟喹诺酮在野生型和突变型DNA旋转酶的喹诺酮结合口袋中的结合能力进行了计算分析，以评估它们的差异结合行为。这项研究表明，DNA旋转酶中的突变改变了结合口袋的特征，导致关键分子相互作用的丧失，从而降低了氟喹诺酮与靶蛋白的结合亲和力。本研究有助于理解由于DNA旋转酶突变导致临床分离株中氟喹诺酮敏感性降低的潜在分子和结构机制。
