For an in vitro mutant of Streptococcus pneumoniae selected on moxifloxacin
four- to eightfold-increased MICs of new fluoroquinolones, only a twofold-
increased MIC of ciprofloxacin, and a twofold-decreased MIC of novobiocin w
ere observed. This phenotype was conferred by two mutations: Ser81Phe in Gy
rA and a novel undescribed His103Tyr mutation in ParE, outside the quinolon
e resistance-determining region, in the putative ATP-binding site of topois
omerase IV.