TABLE 6.

Rates of resistance to JNJ-Q2 and ciprofloxacin in methicillin-resistant S. aureus determined by a modified Luria-Delbruck fluctuation assay

MRSA isolate	QRDR genotype	MIC (μg/ml)a		Resistance rateb
		CIPd	JNJ-Q2	CIP	JNJ-Q2
OC 8532c	Wild type	0.6	0.008	3.7 × 10−12	2.9 × 10−12
OC 8525c	Wild type	3	0.012	1.0 × 10−12	1.4 × 10−12
OC 11150	gyrAS84LparCS80Y	12	0.12	6.0 × 10−10	6.2 × 10−12
OC 15425c	gyrAS84LparCS80F	12	0.12	1.8 × 10−9	3.2 × 10−12

^aAgar MICs were determined through the use of arithmetic dilutions.

^bThe number of mutations isolated per cell per division.

^cIsolates display phenotypic evidence of activated efflux, as the MICs for norfloxacin, benzalkonium chloride, and ethidium bromide were ≥4-fold lower in the presence of 20 μg/ml reserpine.

^dCIP, ciprofloxacin.