TABLE 2.

Antibacterial activities of various quinolones against sequentially acquired quinolone-resistant mutants

Strain and mutanta	MIC (μg/ml)
	Gatifloxacin	Norfloxacin	Ofloxacin	Ciprofloxacin	Tosufloxacin	Sparfloxacin
MS5935	0.05	0.78	0.20	0.20	0.025	0.05
1st	0.20	12.5	0.78	1.56	0.20	0.10
2nd	3.13	100	12.5	12.5	3.13	25
3rd	6.25	200	100	100	25	50
4th	50	200	400	100	25	200
MS5952	0.10	0.78	0.20	0.39	0.05	0.10
1st	0.20	12.5	0.78	1.56	0.20	0.10
2nd	1.56	25	6.25	6.25	3.13	6.25
3rd	3.13	200	50	50	25	6.25
MR5867	0.05	0.78	0.39	0.20	0.025	0.05
1st	0.20	12.5	0.78	1.56	0.20	0.10
2nd	3.13	50	12.5	25	1.56	6.25
3rd	6.25	200	50	100	50	12.5
4th	200	200	400	100	50	200
MR6009	0.10	1.56	0.39	0.39	0.025	0.05
1st	0.20	12.5	0.78	1.56	0.20	0.10
2nd	1.56	50	12.5	12.5	3.13	3.13
3rd	1.56	200	25	100	12.5	6.25
4th	200	200	400	100	25	200

^aAbbreviations: 1st, first-step mutant; 2nd, second-step mutant; 3rd, third-step mutant; 4th, fourth-step mutant. The fourth-step mutant of MS5952 was not obtained from the third-step mutant.