TABLE 1.

MICs of macrolides and related agents for 88 erythromycin-resistant GBS isolates according to known mechanisms of resistance

Group (n) and antimicrobial agent	MICa (μg/ml)
	50%	90%	Range
All isolates (88)b
Erythromycin	4	>128	0.5->128
Azithromycin	16	>128	1->128
Clindamycin	64	>128	0.064->128
Telithromycin	0.125	0.5	0.032-2
ermB (50)
Erythromycin	128	>128	0.5->128
Azithromycin	>128	>128	2->128
Clindamycin	64	>128	0.25->128
Telithromycin	0.125	1	0.064-2
ermA (28)
Erythromycin	2	8	0.5-16
Azithromycin	8	32	1-64
Clindamycin	0.5	128	0.064->128
Telithromycin	0.064	0.064	0.032-0.125
mefA (8)
Erythromycin	2	4	2-4
Azithromycin	2	4	2-4
Clindamycin	0.064	0.125	0.064-0.125
Telithromycin	0.25	0.25	0.125-0.5

^a50 and 90%, MIC₅₀ and MIC₉₀, respectively.

^bTwo isolates were negative for ermA, ermB, and mefA genes.