TABLE 8.

S. pyogenes single-step mutation frequencies

Strain no.	Phenotype (resistance determinant)a	Selecting drug	Frequency of mutation at:
			2× MIC	4× MIC	8× MIC
2132	Macrolide S	CEM-101	<1.0 × 10−10	<1.0 × 10−10	<1.0 × 10−10
		Azithromycin	<1.0 × 10−10	<1.0 × 10−10	<1.0 × 10−10
		Clarithromycin	<1.0 × 10−10	<1.0 × 10−10	<1.0 × 10−10
		Telithromycin	<8.3 × 10−11	<8.3 × 10−11	<8.3 × 10−11
		Clindamycin	<7.7 × 10−11	<7.7 × 10−11	<7.7 × 10−11
2368	Macrolide R [erm(B)]	CEM-101	<5.9 × 10−11	<5.9 × 10−11	<5.9 × 10−11
		Azithromycin	NTb	NT	NT
		Clarithromycin	NT	NT	NT
		Telithromycin	NT	NT	NT
		Clindamycin	NT	NT	NT
2094	Macrolide R [erm(A)]	CEM-101	5.3 × 10−8	2.1 × 10−9	<5.3 × 10−10
		Azithromycin	NT	NT	NT
		Clarithromycin	1.7 × 10−7	1.0 × 10−7	5.0 × 10−9
		Telithromycin	7.7 × 10−8	<1.5 × 10−10	<1.5 × 10−10
		Clindamycin	2.1 × 10−7	1.3 × 10−7	1.1 × 10−7
2011	Macrolide R [mef(A)]	CEM-101	3.9 × 10−8	<1.1 × 10−10	<1.1 × 10−10
		Azithromycin	NT	NT	NT
		Clarithromycin	NT	NT	NT
		Telithromycin	3.8 × 10−8	<6.3 × 10−10	<6.3 × 10−10
		Clindamycin	<1.0 × 10−10	<1.0 × 10−10	<1.0 × 10−10
237	Macrolide-R (L4 mutation)	CEM-101	<1.3 × 10−10	<1.3 × 10−10	<1.3 × 10−10
		Azithromycin	NT	NT	NT
		Clarithromycin	<3.3 × 10−10	<3.3 × 10−10	<3.3 × 10−10
		Telithromycin	<2.0 × 10−10	<2.0 × 10−10	<2.0 × 10−10
		Clindamycin	<1.0 × 10−10	<1.0 × 10−10	<1.0 × 10−10

^aS, susceptible; R, resistant.

^bNT, not tested.