María M. Tavío

María M. Tavío

University of Las Palmas de Gran Canaria, Spain

Title: Qnr proteins: Structure and properties against quinolone inhibition of DNA gyrase


María M. Tavío M.D. completed her Ph.D. at the age of 27 years from the University of Las Palmas de Gran Canaria and postdoctoral studies from The London Hospital Medical College, Queen Mary´s University of London and the Faculty of Medicine of L´ Aquila University. She is titular professor at the University of Las Palmas de Gran Canaria. She has published more than 40 papers on quinolone and beta-lactam resistance including the article on QnrS1 protein characterization derived from her recent work at Harvard Medical School. She also serves as assessor for national and European research projects on antimicrobial resistance.


Quinolones are commonly prescribed antimicrobial agents in clinical practice, however an increasing number of quinolone resistant strains have appeared in the last decade. Qnr proteins are spread among clinical isolates and contribute to quinolone resistance; they block quinolone inhibition of bacterial DNA gyrase and topoisomerase IV. Their beta-helical structure is interrupted by Loop A (8 amino acids) and Loop B (12 amino acids), this larger loop with a significant role in quinolone resistance. The present study analyzed 168 sequences of different Qnr proteins that are available at several databases, together with our own results and those from previous published studies that were obtained using cloning, site-directed mutagenesis and determination of the fluoroquinolone MICs in strains with mutated Qnr proteins. The study was focused on the conserved residues within the positions Ser36 to Asp63 including the loop A and the positions Gln92 to Tyr123 including the loop B (following QnrB numbering). The analysis revealed that conserved amino acids with a more significant role in increasing fluoroquinolone MICs in E. coli strains were: Phe40, Phe56, Phe96, Phe101, Phe111, Cys43, Cys112, Gly53, Gly93, Leu121, Ser113, Ala114, Ile116 and Tyr123 in the 96 QnrB and 9 QnrD proteins, and their equivalent amino acids in the 28 analyzed sequences of QnrA proteins, 23 of QnrS, 9 of QnrVC, 2 of QnrVV and 1 of QnrC protein. Notably, the comparison of QnrB1 with the remaining Qnr proteins showed that the 10 residues located at the C-terminal position following the loop A and loop B amino acid sequences showed 50-60% similarities.