TABLE 6.

S. pyogenes multistep selection results

Strain no.	Phenotype (resistance determinant)a	Antibioticb	Initial MIC (μg/ml)	Selected resistance		Retest MIC (μg/ml)c after passages in subinhibitory concns of the following antibiotic and 10 antibiotic-free subcultures:
				MIC (μg/ml)	No. of passages	CEM	AZI	CLA	TEL	CLI
2132	Macrolide S	CEM	0.008	0.016	50
		AZI	0.06	1	28	0.016	1	0.25	0.03	0.03
		CLA	0.03	0.016	50
		TEL	0.008	0.03	50
		CLI	0.06	0.06	50
2368	Macrolide R [erm(B)]	CEM	1	8	18	8	>64	>64	>64	>64
		AZI	>64	NTd	NT
		CLA	>64	NT	NT
		TEL	8	>64	6	0.5	>64	>64	>64	>64
		CLI	>64	NT	NT
2094	Macrolide R [erm(A)]	CEM	0.03	0.25	43	0.25	4	8	0.5	0.06
		AZI	4	>64	5	0.016	>64	1	0.03	0.06
		CLA	0.5	>64	6	0.016	>64	>64	0.03	0.06
		TEL	0.03	0.25	22	0.03	>64	8	0.125	>64
		CLI	0.06	>64	34	0.03	16	1	0.03	>64
2011	Macrolide R [mef(A)]	CEM	0.125	0.125	50
		AZI	4	32	35	0.06	16	4	0.25	0.06
		CLA	4	8	50
		TEL	0.5	1	50
		CLI	0.06	0.06	50
237	Macrolide R (L4 mutation)	CEM	0.03	0.25	20	0.5	4	1	1	0.03
		AZI	4	8	50
		CLA	0.25	1	50
		TEL	0.06	0.125	50
		CLI	0.06	0.5	43	0.03	8	0.5	0.06	1

^aS, susceptible; R, resistant.

^bCEM, CEM-101; AZI, azithromycin; CLA, clarithromycin; TEL, telithromycin; CLI, clindamycin.

^cBoldface indicates cross-reactivity.

^dNT, not tested.