TABLE 3.

Effect of C-8 substituent on identity of third-step resistance allele in S. aureus

Straina	Fluoroquinolone for selectionb	C-8 substituent	C-7 ring alkyl	Variants recoveredc
				GyrA	ParC
KD2062	PD138032	H	3′ C-methyl	S85P
KD2063	PD138032	H	3′ C-methyl	S85P	—
KD2064	PD138032	H	3′ C-methyl	S85P	—
KD2065	PD163753	Br	3′ C-methyl	S85P	—
KD2066	PD163753	Br	3′ C-methyl	S85P	—
KD2067	PD163753	Br	3′ C-methyl	—d	—d
KD2068	PD138124	Cl	3′ C-methyl	S85P	—
KD2069	PD138124	Cl	3′ C-methyl	—d	—d
KD2070	PD138124	Cl	3′ C-methyl		E84K
KD2071	PD135432	OMe	3′ C-methyl	S85P	—
KD2072	PD135432	OMe	3′ C-methyl	S85P	—
KD2073	Ciprofloxacin	H	None	S85P	—
KD2074	Ciprofloxacin	H	None	S85P	—
KD2075	Ciprofloxacin	H	None	—d	—d
KD2076	Sparfloxacin	F	3′,5′ dimethyl	S85P	—
KD2077	Sparfloxacin	F	3′,5′ dimethyl	S85P	—
KD2078	Sparfloxacin	F	3′,5′ dimethyl	S85P	—

^aParental strain for selection of mutants was S. aureus EN1252, a GyrA (S84L)-ParC (S80F) double mutant. Strain numbers listed are for third-step mutants. 

^bMutants were selected on GL agar plates containing two to three -times the MIC₉₉ (listed in Table 1) for each compound. 

^cGyrA (DNA gyrase) and ParC (DNA topoisomerase IV; also called GrlA in S. aureus) variants. Variants are indicated with the wild-type amino acid preceeding the amino acid number, which is followed by the variant amino acid. Amino acid abbreviations: A, alanine; E, glutamic acid; F, phenylalanine, K, lysine; P, proline; S, serine; V, valine. —, QRDR had no changes relative to the parental strain. 

^dQRDR of gyrB and parE (grlB) had no changes relative to the parental strain.