Levofloxacin in vitro activity and time-kill evaluation of Stenotrophomonas maltophilia clinical isolates

The in vitro activity of levofloxacin and eight other antimicrobial agents against 60 clinical isolates of Stenotrophomonas maltophilia was determined by an agar dilution method using 10(4) and 10(6) cfu/spot inocula. At the lower inoculum, 85.0% of the isolates were susceptible to levofloxacin but only 58.3% were susceptible to ofloxacin; at the higher inoculum, 78.3% were susceptible to levofloxacin and 36.7% to ofloxacin. In time-kill studies, levofloxacin exerted bactericidal activity within 4 h. With ofloxacin and ciprofloxacin bacterial regrowth was observed after 8 h. Levofloxacin may represent an alternative drug in the treatment of infections caused by S. maltophilia.