title: Structure based in silico analysis of quinolone resistance in clinical isolates of Salmonella Typhi from India.
abstract: 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.
authors.affiliation: Department of Biophysics, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Manoj
authors.initials: M
authors.lastname: Kumar
authors.affiliation: Department of Microbiology, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Sushila
authors.initials: S
authors.lastname: Dahiya
authors.affiliation: Department of Microbiology, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Priyanka
authors.initials: P
authors.lastname: Sharma
authors.affiliation: Department of Biophysics, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Sujata
authors.initials: S
authors.lastname: Sharma
authors.affiliation: Department of Biophysics, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Tej P
authors.initials: TP
authors.lastname: Singh
authors.affiliation: Department of Microbiology, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Arti
authors.initials: A
authors.lastname: Kapil
authors.affiliation: Department of Biophysics, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Punit
authors.initials: P
authors.lastname: Kaur
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000494:pharmacology*; D003198:Computer Simulation; D027081:DNA Gyrase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D024881:Drug Resistance, Bacterial; D006801:Humans; D007194:India; D008826:Microbial Sensitivity Tests; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D056004:Molecular Dynamics Simulation; D015394:Molecular Structure; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D015363:Quinolones / Q000737:chemistry* / Q000494:pharmacology*; D012485:Salmonella typhi / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D013329:Structure-Activity Relationship
chemical_list: D000900:Anti-Bacterial Agents; D015363:Quinolones; D027081:DNA Gyrase