In this study delafloxacin resistance mechanisms in Escherichia coli strains were
analyzed. Delafloxacin is a new fluoroquinolone, that is approved for clinical application
however, resistance against this agent is scarcely reported. In our study 37 E. coli
strains were included and antimicrobial susceptibility testing was performed for ciprofloxacin,
delafloxacin, levofloxacin, moxifloxacin, ceftazidime, cefotaxime, imipenem. Six delafloxacin
resistant E. coli strains were selected for whole-genome sequencing and all of them
exhibited resistance to other fluoroquinonlones and showed an extended-spectrum beta-lactamase
phenotype. The six delafloxacin resistant E. coli strains belonged to different sequence
types (STs) namely, ST131 (2 strains), ST57 (2 strains), ST162 and ST15840. Each delafloxacin
resistant strain possessed multiple mutations in quinolone resistance-determining
regions (QRDRs). Notably, three mutations in gyrA Ser83Leu, Asp87Asn and parC Ser80Ile
were in strains of ST162, ST57 and ST15840. However, the two strains of ST131 carried
five combined mutations namely, gyrA Ser83Leu, Asp87Asn, parC Ser80Ile, Glu84Val,
parE Ile549Leu. Association of delafloxacin resistance and production of CTX-M-15
in ST131, CMY-2 in ST162 and ST15840 was detected. In this study a new ST, ST15840
of clonal complex 69 was identified. Our results demonstrate, that at least three
mutations in QRDRs are required for delafloxacin resistance in E. coli.