Alternative Pathways to Ciprofloxacin Resistance in Neisseria   gonorrhoeae : An In Vitro Study of the WHO-P and WHO-F Reference Strains.

Emerging resistance to ceftriaxone and azithromycin has led to renewed interest in using ciprofloxacin to treat Neisseria gonorrhoeae . This could lead to the rapid emergence and spread of ciprofloxacin resistance. Previous studies investigating the emergence of fluoroquinolone resistance have been limited to a single strain of N. gonorrhoeae . It is unknown if different genetic backgrounds affect the evolution of fluoroquinolone resistance in N. gonorrhoeae , as has been shown in other bacterial species. This study evaluated the molecular pathways leading to ciprofloxacin resistance in two reference strains of N. gonorrhoeae -WHO-F and WHO-P. Three clones of each of the two strains of N. gonorrhoeae were evolved in the presence of ciprofloxacin, and isolates from different time points were whole-genome sequenced. We found evidence of strain-specific differences in the emergence of ciprofloxacin resistance. Two out of three clones from WHO-P followed the canonical pathway to resistance proceeding via substitutions in GyrA-S91F, GyrA-D95N and ParC. None of the three WHO-F clones followed this pathway. In addition, mutations in gyrB , uvrA and rne frequently occurred in WHO-F clones, whereas mutations in yhgF , porB and potA occurred in WHO-P.