Global Phenotypic Characterization of Effects of Fluoroquinolone Resistance Selection on the Metabolic Activities and Drug Susceptibilities of Clostridium perfringens Strains

Table 3

Comparison of the effect of fluoroquinolone resistance selection on the MIC of various antimicrobial agents and ethidium bromide. Ethidium bromide concentrations in the plates were 0, 2, 4, 5, 6, 8, and 10 µg/mL.

C.  perfringens strains	MIC (µg/mL), as shown by Etest for antimicrobial agents or agar dilution for ethidium bromide
	Erythromycin	Amoxicillin	Ceftriaxone	Gentamicin	Chloramphenicol	Cefoxitin	Metronidazole	Ethidium bromide
3626
W	2	0.1	1	128	3	1	1.5	6
NR	1.5	0.19^*a	0.016	48	8^*	0.25	3^*	10^**b
CR	0.5	0.1	4^*	12	2	1	1.5	10^**
GR	1	0.25^*	0.016	64	6^*	2^*	3^*	5
13124
W	2	0.25	64	512	8	4	3	4
NR	0.75	0.125	16	64	3	1.5	1.5	2
CR	1.5	0.75^*	32	128	8	2	4^*	4
GR	1	2^*	12	256	3	4	1.5	2
NCTR
W	2	0.13	4	128	4	0.38	1.5	2
NR	0.75	0.2	0.016	128	3	0.75^*	0.75	10^**
CR	1	0.2	3	48	4	0.5	1	10^**
GR	0.75	0.1	1	32	3	1^*	1.5	10^**
VPI
W	1.5	0.25	16	384	3	0.75	3	6
NR	3	0.38	16	64	4	1.5^*	3	8^**
CR	1.5	1.5^*	16	256	3	3^*	2	10^**
GR	0.75	0.5^*	64^*	256	6^*	2^*	3	8^**

The indicates that fluoroquinolone resistance selection resulted in a decrease in susceptibility; W, NR, CR, and GR refer to wild type, norfloxacin-resistant, ciprofloxacin-resistant, and gatifloxacin-resistant, respectively. ^b**Resistant strains grew on the plates containing 10 µg/mL of ethidium bromide, so the MIC of the ethidium bromide was greater than 10 µg/mL for these strains.