TABLE 7.

S. pneumoniae single-step mutation frequencies

Strain no.	Phenotype (resistance determinant)a	Selecting drug	Frequency of mutation at:
			2× MIC	4× MIC	8× MIC
1077	Macrolide S	CEM-101	<9.1 × 10−9	<9.1 × 10−9	<9.1 × 10−9
		Azithromycin	7.2 × 10−9	<1.9 × 10−10	<1.9 × 10−10
		Clarithromycin	1.1 × 10−9	<1.2 × 10−10	<1.2 × 10−10
		Telithromycin	1.1 × 10−9	<5.5 × 10−10	<5.5 × 10−10
		Clindamycin	<3.8 × 10−10	<3.8 × 10−10	<3.8 × 10−10
24	Macrolide R [erm(B)]	CEM-101	1.8 × 10−7	<5.0 × 10−9	<5.0 × 10−9
		Azithromycin	NTb	NT	NT
		Clarithromycin	NT	NT	NT
		Telithromycin	1.3 × 10−4	2.5 × 10−6	1.7 × 10−6
		Clindamycin	NT	NT	NT
3665	Macrolide R [mef(A)]	CEM-101	6.8 × 10−7	1.4 × 10−7	<4.5 × 10−10
		Azithromycin	NT	NT	NT
		Clarithromycin	5.0 × 10−7	<5.0 × 10−10	<5.0 × 10−10
		Telithromycin	7.5 × 10−9	2.5 × 10−9	<2.5 × 10−10
		Clindamycin	<2.4 × 10−10	<2.4 × 10−10	<2.4 × 10−10
1076	Macrolide R [erm(B) mef(A)]	CEM-101	<2.5 × 10−8	7.5 × 10−9	2.0 × 10−9
		Azithromycin	NT	NT	NT
		Clarithromycin	NT	NT	NT
		Telithromycin	6.5 × 10−6	9.7 × 10−6	4.8 × 10−6
		Clindamycin	NT	NT	NT
1635	Macrolide R [erm(A)]	CEM-101	1.6 × 10−8	<2.0 × 10−10	<2.0 × 10−10
		Azithromycin	<2.0 × 10−10	<2.0 × 10−10	<2.0 × 10−10
		Clarithromycin	<3.1 × 10−9	<3.1 × 10−9	<3.1 × 10−9
		Telithromycin	<2.7 × 10−9	<2.7 × 10−9	<2.7 × 10−9
		Clindamycin	7.3 × 10−7	5.5 × 10−7	5.6 × 10−7
2686	Macrolide R (L4 mutation)	CEM-101	<2.5 × 10−9	<2.5 × 10−9	<2.5 × 10−9
		Azithromycin	NT	NT	NT
		Clarithromycin	NT	NT	NT
		Telithromycin	2.2 × 10−5	2.2 × 10−9	<1.1 × 10−9
		Clindamycin	<1.2 × 10−9	<1.2 × 10−9	<1.2 × 10−9
7127	Macrolide S (S20N in L4, A105V in L22)	CEM-101	<2.0 × 10−10	<2.0 × 10−10	<2.0 × 10−10
		Azithromycin	<2.0 × 10−10	<2.0 × 10−10	<2.0 × 10−10
		Clarithromycin	<1.0 × 10−9	<1.0 × 10−9	<1.0 × 10−9
		Telithromycin	<5.0 × 10−9	<5.0 × 10−9	<5.0 × 10−9
		Clindamycin	<2.9 × 10−8	<2.9 × 10−8	<2.9 × 10−8
3009	Macrolide R (23S rRNA mutation)	CEM-101	<5.9 × 10−9	<5.9 × 10−9	<5.9 × 10−9
		Azithromycin	NT	NT	NT
		Clarithromycin	NT	NT	NT
		Telithromycin	3.8 × 10−7	<1.5 × 10−10	<1.5 × 10−10
		Clindamycin	1.7 × 10−4	7.3 × 10−9	<1.2 × 10−10

^aS, susceptible; R, resistant.

^bNT, not tested.