Prevalence of single mutations in topoisomerase type II genes among levofloxacin-susceptible clinical strains of Streptococcus pneumoniae isolated in the United States in 1992 to 1996 and 1999 to 2000 - Davies,T.A.; Evangelista,A.; Pfleger,S.; Bush,K.; Sahm,D.F.; Goldschmidt,R. (Antimicrob Agents Chemother, 2002)