TABLE 3.

Susceptibilities of test organisms before and after 10 serial passages with subinhibitory concentrations of ciprofloxacin, levofloxacin, and trovafloxacin

Microorganism	Initial no. of isolates tested	Fluoroquinolone	MIC (μg/ml)
			Pre-serial passage			Post-serial passage
			Range	50%a	90%b	Range	50%	90%
MSSA	13	Ciprofloxacin	0.12–0.5	0.25	0.5	4–256	16	64
		Levofloxacin	0.12–0.25	0.25	0.5	0.5–4	1	32
		Trovafloxacin	0.004–0.01	0.004	0.01	0.125–32	0.25	4
MRSA	15	Ciprofloxacin	0.12–1	0.25	0.5	1–256	8	128
		Levofloxacin	0.06–0.5	0.25	0.5	1–32	2	32
		Trovafloxacin	0.008–0.12	0.008	0.12	0.03–2	0.25	2
E. coli	20	Ciprofloxacin	0.004–0.12	0.008	0.016	0.012–128	1.0	16
		Levofloxacin	0.03–0.25	0.03	0.06	0.5–16	2.0	8
		Trovafloxacin	0.002–0.03	0.008	0.016	0.5–16	2.0	4
K. pneumoniae	20	Ciprofloxacin	0.016–0.25	0.06	0.12	2–64	16	64
		Levofloxacin	0.03–0.25	0.03	0.12	2–128	8	32
		Trovafloxacin	0.03–0.5	0.06	0.12	2–128	16	128
E. cloacae	19	Ciprofloxacin	0.008–0.06	0.03	0.06	0.5–128	8	64
		Levofloxacin	0.004–0.12	0.06	0.12	4–64	8	64
		Trovafloxacin	0.03–0.5	0.06	0.25	8–64	16	64
S. marcescens	16	Ciprofloxacin	0.06–0.25	0.25	0.25	2–64	16	64
		Levofloxacin	0.06–0.5	0.25	0.5	1–256	16	128
		Trovafloxacin	0.06–0.25	0.12	0.25	32–256	64	256
P. aeruginosa	20	Ciprofloxacin	0.03–1	0.12	0.25	2–256	8	32
		Levofloxacin	0.12–1	0.5	1	16–256	128	256
		Trovafloxacin	0.06–1	0.25	1	32–256	256	256

^aMIC₅₀. 

^bMIC₉₀.