TABLE 2.

Gene mutations in quinolone resistance-determining region and antibacterial activities of various quinolones against the resistant mutants^a

Strain	Selecting quinolone (concn [μg/ml])b	No. of isolates	Mutation (codon)c		MIC (μg/ml)
			gyrA	parC	Gat	Spa	Tro	Lev	Cip	Nor
Parent			None	None	0.39	0.39	0.10	0.78	0.78	6.25
Mutant
Type I	Tro (0.20)	3	None	Ser79(TCT)→Tyr(TAT)	0.39	0.39	0.39	1.56	3.13	25
	Lev (3.13)	1	None	Asp83(GAT)→Asn(AAT)	0.39	0.39	0.39	1.56	3.13	25
	Lev (3.13)	2	None	Ser79(TCT)→Tyr(TAT)	0.39	0.39	0.39	1.56	3.13	25
	Nor (12.5 or 25)	3	None	Ser79(TCT)→Tyr(TAT)	0.39	0.39	0.39	1.56	3.13	25
	Cip (1.56)	1	None	Ser79(TCT)→Tyr(TAT)	0.39	0.39	0.39	1.56	3.13	25
	Cip (1.56)	2	None	Asp83(GAT)→Asn(AAT)	0.39	0.39	0.39	1.56	3.13	25
Type II	Spa (3.13 or 6.25)	3	Ser81(TCC)→Phe(TTC)	None	0.78	3.13	0.10	0.78	0.78	6.25
	Gat (0.39)	1	Ser81(TCC)→Tyr(TAC)	None	0.78	3.13	0.10	0.78	0.78	6.25
Type III	Tro (0.20 or 0.39)	3	None	None	0.39	0.78	0.39	0.78	0.78	6.25

^aThe mutants were selected on the plates containing the selecting agents after at least a 48 h of incubation at 37°C. On the other hand, the MICs were defined as the lowest concentrations at which no visible growth was observed after incubation at 37°C for 18 to 20 h. None of the strains possessed mutations in the QRDR of gyrB and parE genes. Abbreviations: Gat, gatifloxacin; Spa, sparfloxacin; Tro, trovafloxacin; Lev, levofloxacin; Nor, norfloxacin; Cip, ciprofloxacin. 

^bThe concentrations of the agents used for selection. 

^cThe codon positions of gyrA and parC are designated according to the numbering of Balas et al. (1) and Pan and Fisher (12), respectively.