The qnrA gene encodes a pentapeptide repeat protein that protects DNA gyrase and topoisomerase IV from quinolone inhibition. qnrA (and its relatives qnrB, qnrS) confer low-level resistance to fluoroquinolones (raising MICs modestly) and facilitate the selection of high-level resistance mutations. Detection of qnrA in a pathogen suggests that fluoroquinolone therapy may be less effective and that stepwise mutations to high-level resistance are likely (Strahilevitz et al. 2009, Jacoby et al. 2014, Rodriguez-Martines et al. 2016).
Strahilevitz, J., Jacoby, G. A., Hooper, D. C., & Robicsek, A. (2009). Plasmid-mediated quinolone resistance: a multifaceted threat. Clinical microbiology reviews, 22(4), 664–689.
Jacoby, G. A., Strahilevitz, J., & Hooper, D. C. (2014). Plasmid-mediated quinolone resistance. Microbiology spectrum, 2(5), 10.1128/microbiolspec.PLAS-0006-2013.
Rodríguez-Martínez, J. M., Machuca, J., Cano, M. E., Calvo, J., Martínez-Martínez, L., & Pascual, A. (2016). Plasmid-mediated quinolone resistance: Two decades on. Drug resistance updates : reviews and commentaries in antimicrobial and anticancer chemotherapy, 29, 13–29.
